颜色格式转换： FFmpeg源代码简单分析：libswscale的sws

http://blog.csdn.net/leixiaohua1020/article/details/44305697

目录(?)[+]

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FFmpeg的库函数源代码分析文章列表：

【架构图】

FFmpeg源代码结构图 - 解码

FFmpeg源代码结构图 - 编码

【通用】

FFmpeg 源代码简单分析：av_register_all()

FFmpeg 源代码简单分析：avcodec_register_all()

FFmpeg 源代码简单分析：内存的分配和释放（av_malloc()、av_free()等）

FFmpeg 源代码简单分析：常见结构体的初始化和销毁（AVFormatContext，AVFrame等）

FFmpeg 源代码简单分析：avio_open2()

FFmpeg 源代码简单分析：av_find_decoder()和av_find_encoder()

FFmpeg 源代码简单分析：avcodec_open2()

FFmpeg 源代码简单分析：avcodec_close()

【解码】

图解FFMPEG打开媒体的函数avformat_open_input

FFmpeg 源代码简单分析：avformat_open_input()

FFmpeg 源代码简单分析：avformat_find_stream_info()

FFmpeg 源代码简单分析：av_read_frame()

FFmpeg 源代码简单分析：avcodec_decode_video2()

FFmpeg 源代码简单分析：avformat_close_input()

【编码】

FFmpeg 源代码简单分析：avformat_alloc_output_context2()

FFmpeg 源代码简单分析：avformat_write_header()

FFmpeg 源代码简单分析：avcodec_encode_video()

FFmpeg 源代码简单分析：av_write_frame()

FFmpeg 源代码简单分析：av_write_trailer()

【其它】

FFmpeg源代码简单分析：日志输出系统（av_log()等）

FFmpeg源代码简单分析：结构体成员管理系统-AVClass

FFmpeg源代码简单分析：结构体成员管理系统-AVOption

FFmpeg源代码简单分析：libswscale的sws_getContext()

FFmpeg源代码简单分析：libswscale的sws_scale()

FFmpeg源代码简单分析：libavdevice的avdevice_register_all()

FFmpeg源代码简单分析：libavdevice的gdigrab

【脚本】

FFmpeg源代码简单分析：makefile

FFmpeg源代码简单分析：configure

【H.264】

FFmpeg的H.264解码器源代码简单分析：概述

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打算写两篇文章记录FFmpeg中的图像处理（缩放，YUV/RGB格式转换）类库libswsscale的源代码。libswscale是一个主要用于处理图片像素数据的类库。可以完成图片像素格式的转换，图片的拉伸等工作。有关libswscale的使用可以参考文章：

《最简单的基于FFmpeg的libswscale的示例（YUV转RGB）》

libswscale常用的函数数量很少，一般情况下就3个：

sws_getContext()：初始化一个SwsContext。

sws_scale()：处理图像数据。

sws_freeContext()：释放一个SwsContext。

其中sws_getContext()也可以用sws_getCachedContext()取代。

尽管libswscale从表面上看常用函数的个数不多，它的内部却有一个大大的“世界”。做为一个几乎“万能”的图片像素数据处理类库，它的内部包含了大量的代码。因此计划写两篇文章分析它的源代码。本文首先分析它的初始化函数sws_getContext()，而下一篇文章则分析它的数据处理函数sws_scale()。

函数调用结构图

分析得到的libswscale的函数调用关系如下图所示。

Libswscale处理数据流程

Libswscale处理像素数据的流程可以概括为下图。

从图中可以看出，libswscale处理数据有两条最主要的方式：unscaled和scaled。unscaled用于处理不需要拉伸的像素数据（属于比较特殊的情况），scaled用于处理需要拉伸的像素数据。Unscaled只需要对图像像素格式进行转换；而Scaled则除了对像素格式进行转换之外，还需要对图像进行缩放。Scaled方式可以分成以下几个步骤：

XXX to YUV Converter：首相将数据像素数据转换为8bitYUV格式；
Horizontal scaler：水平拉伸图像，并且转换为15bitYUV；
Vertical scaler：垂直拉伸图像；
Output converter：转换为输出像素格式。

SwsContext

SwsContext是使用libswscale时候一个贯穿始终的结构体。但是我们在使用FFmpeg的类库进行开发的时候，是无法看到它的内部结构的。在libswscale\swscale.h中只能看到一行定义：

[cpp] view plaincopy

struct SwsContext;

一般人看到这个只有一行定义的结构体，会猜测它的内部一定十分简单。但是假使我们看一下FFmpeg的源代码，会发现这个猜测是完全错误的——SwsContext的定义是十分复杂的。它的定义位于libswscale\swscale_internal.h中，如下所示。

[cpp] view plaincopy

/* This struct should be aligned on at least a 32-byte boundary. */
typedef struct SwsContext {
/**
* info on struct for av_log
*/
const AVClass *av_class;
/**
* Note that src, dst, srcStride, dstStride will be copied in the
* sws_scale() wrapper so they can be freely modified here.
*/
SwsFunc swscale;
int srcW; ///< Width of source luma/alpha planes.
int srcH; ///< Height of source luma/alpha planes.
int dstH; ///< Height of destination luma/alpha planes.
int chrSrcW; ///< Width of source chroma planes.
int chrSrcH; ///< Height of source chroma planes.
int chrDstW; ///< Width of destination chroma planes.
int chrDstH; ///< Height of destination chroma planes.
int lumXInc, chrXInc;
int lumYInc, chrYInc;
enum AVPixelFormat dstFormat; ///< Destination pixel format.
enum AVPixelFormat srcFormat; ///< Source pixel format.
int dstFormatBpp; ///< Number of bits per pixel of the destination pixel format.
int srcFormatBpp; ///< Number of bits per pixel of the source pixel format.
int dstBpc, srcBpc;
int chrSrcHSubSample; ///< Binary logarithm of horizontal subsampling factor between luma/alpha and chroma planes in source image.
int chrSrcVSubSample; ///< Binary logarithm of vertical subsampling factor between luma/alpha and chroma planes in source image.
int chrDstHSubSample; ///< Binary logarithm of horizontal subsampling factor between luma/alpha and chroma planes in destination image.
int chrDstVSubSample; ///< Binary logarithm of vertical subsampling factor between luma/alpha and chroma planes in destination image.
int vChrDrop; ///< Binary logarithm of extra vertical subsampling factor in source image chroma planes specified by user.
int sliceDir; ///< Direction that slices are fed to the scaler (1 = top-to-bottom, -1 = bottom-to-top).
double param[2]; ///< Input parameters for scaling algorithms that need them.
/* The cascaded_* fields allow spliting a scaler task into multiple
* sequential steps, this is for example used to limit the maximum
* downscaling factor that needs to be supported in one scaler.
*/
struct SwsContext *cascaded_context[2];
int cascaded_tmpStride[4];
uint8_t *cascaded_tmp[4];
uint32_t pal_yuv[256];
uint32_t pal_rgb[256];
/**
* @name Scaled horizontal lines ring buffer.
* The horizontal scaler keeps just enough scaled lines in a ring buffer
* so they may be passed to the vertical scaler. The pointers to the
* allocated buffers for each line are duplicated in sequence in the ring
* buffer to simplify indexing and avoid wrapping around between lines
* inside the vertical scaler code. The wrapping is done before the
* vertical scaler is called.
*/
//@{
int16_t **lumPixBuf; ///< Ring buffer for scaled horizontal luma plane lines to be fed to the vertical scaler.
int16_t **chrUPixBuf; ///< Ring buffer for scaled horizontal chroma plane lines to be fed to the vertical scaler.
int16_t **chrVPixBuf; ///< Ring buffer for scaled horizontal chroma plane lines to be fed to the vertical scaler.
int16_t **alpPixBuf; ///< Ring buffer for scaled horizontal alpha plane lines to be fed to the vertical scaler.
int vLumBufSize; ///< Number of vertical luma/alpha lines allocated in the ring buffer.
int vChrBufSize; ///< Number of vertical chroma lines allocated in the ring buffer.
int lastInLumBuf; ///< Last scaled horizontal luma/alpha line from source in the ring buffer.
int lastInChrBuf; ///< Last scaled horizontal chroma line from source in the ring buffer.
int lumBufIndex; ///< Index in ring buffer of the last scaled horizontal luma/alpha line from source.
int chrBufIndex; ///< Index in ring buffer of the last scaled horizontal chroma line from source.
//@}
uint8_t *formatConvBuffer;
/**
* @name Horizontal and vertical filters.
* To better understand the following fields, here is a pseudo-code of
* their usage in filtering a horizontal line:
* @code
* for (i = 0; i < width; i++) {
* dst[i] = 0;
* for (j = 0; j < filterSize; j++)
* dst[i] += src[ filterPos[i] + j ] * filter[ filterSize * i + j ];
* dst[i] >>= FRAC_BITS; // The actual implementation is fixed-point.
* }
* @endcode
*/
//@{
int16_t *hLumFilter; ///< Array of horizontal filter coefficients for luma/alpha planes.
int16_t *hChrFilter; ///< Array of horizontal filter coefficients for chroma planes.
int16_t *vLumFilter; ///< Array of vertical filter coefficients for luma/alpha planes.
int16_t *vChrFilter; ///< Array of vertical filter coefficients for chroma planes.
int32_t *hLumFilterPos; ///< Array of horizontal filter starting positions for each dst[i] for luma/alpha planes.
int32_t *hChrFilterPos; ///< Array of horizontal filter starting positions for each dst[i] for chroma planes.
int32_t *vLumFilterPos; ///< Array of vertical filter starting positions for each dst[i] for luma/alpha planes.
int32_t *vChrFilterPos; ///< Array of vertical filter starting positions for each dst[i] for chroma planes.
int hLumFilterSize; ///< Horizontal filter size for luma/alpha pixels.
int hChrFilterSize; ///< Horizontal filter size for chroma pixels.
int vLumFilterSize; ///< Vertical filter size for luma/alpha pixels.
int vChrFilterSize; ///< Vertical filter size for chroma pixels.
//@}
int lumMmxextFilterCodeSize; ///< Runtime-generated MMXEXT horizontal fast bilinear scaler code size for luma/alpha planes.
int chrMmxextFilterCodeSize; ///< Runtime-generated MMXEXT horizontal fast bilinear scaler code size for chroma planes.
uint8_t *lumMmxextFilterCode; ///< Runtime-generated MMXEXT horizontal fast bilinear scaler code for luma/alpha planes.
uint8_t *chrMmxextFilterCode; ///< Runtime-generated MMXEXT horizontal fast bilinear scaler code for chroma planes.
int canMMXEXTBeUsed;
int dstY; ///< Last destination vertical line output from last slice.
int flags; ///< Flags passed by the user to select scaler algorithm, optimizations, subsampling, etc...
void *yuvTable; // pointer to the yuv->rgb table start so it can be freed()
// alignment ensures the offset can be added in a single
// instruction on e.g. ARM
DECLARE_ALIGNED(16, int, table_gV)[256 + 2*YUVRGB_TABLE_HEADROOM];
uint8_t *table_rV[256 + 2*YUVRGB_TABLE_HEADROOM];
uint8_t *table_gU[256 + 2*YUVRGB_TABLE_HEADROOM];
uint8_t *table_bU[256 + 2*YUVRGB_TABLE_HEADROOM];
DECLARE_ALIGNED(16, int32_t, input_rgb2yuv_table)[16+40*4]; // This table can contain both C and SIMD formatted values, the C vales are always at the XY_IDX points
#define RY_IDX 0
#define GY_IDX 1
#define BY_IDX 2
#define RU_IDX 3
#define GU_IDX 4
#define BU_IDX 5
#define RV_IDX 6
#define GV_IDX 7
#define BV_IDX 8
#define RGB2YUV_SHIFT 15
int *dither_error[4];
//Colorspace stuff
int contrast, brightness, saturation; // for sws_getColorspaceDetails
int srcColorspaceTable[4];
int dstColorspaceTable[4];
int srcRange; ///< 0 = MPG YUV range, 1 = JPG YUV range (source image).
int dstRange; ///< 0 = MPG YUV range, 1 = JPG YUV range (destination image).
int src0Alpha;
int dst0Alpha;
int srcXYZ;
int dstXYZ;
int src_h_chr_pos;
int dst_h_chr_pos;
int src_v_chr_pos;
int dst_v_chr_pos;
int yuv2rgb_y_offset;
int yuv2rgb_y_coeff;
int yuv2rgb_v2r_coeff;
int yuv2rgb_v2g_coeff;
int yuv2rgb_u2g_coeff;
int yuv2rgb_u2b_coeff;
#define RED_DITHER "0*8"
#define GREEN_DITHER "1*8"
#define BLUE_DITHER "2*8"
#define Y_COEFF "3*8"
#define VR_COEFF "4*8"
#define UB_COEFF "5*8"
#define VG_COEFF "6*8"
#define UG_COEFF "7*8"
#define Y_OFFSET "8*8"
#define U_OFFSET "9*8"
#define V_OFFSET "10*8"
#define LUM_MMX_FILTER_OFFSET "11*8"
#define CHR_MMX_FILTER_OFFSET "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)
#define DSTW_OFFSET "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2"
#define ESP_OFFSET "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+8"
#define VROUNDER_OFFSET "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+16"
#define U_TEMP "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+24"
#define V_TEMP "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+32"
#define Y_TEMP "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+40"
#define ALP_MMX_FILTER_OFFSET "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*2+48"
#define UV_OFF_PX "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*3+48"
#define UV_OFF_BYTE "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*3+56"
#define DITHER16 "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*3+64"
#define DITHER32 "11*8+4*4*"AV_STRINGIFY(MAX_FILTER_SIZE)"*3+80"
#define DITHER32_INT (11*8+4*4*MAX_FILTER_SIZE*3+80) // value equal to above, used for checking that the struct hasn't been changed by mistake
DECLARE_ALIGNED(8, uint64_t, redDither);
DECLARE_ALIGNED(8, uint64_t, greenDither);
DECLARE_ALIGNED(8, uint64_t, blueDither);
DECLARE_ALIGNED(8, uint64_t, yCoeff);
DECLARE_ALIGNED(8, uint64_t, vrCoeff);
DECLARE_ALIGNED(8, uint64_t, ubCoeff);
DECLARE_ALIGNED(8, uint64_t, vgCoeff);
DECLARE_ALIGNED(8, uint64_t, ugCoeff);
DECLARE_ALIGNED(8, uint64_t, yOffset);
DECLARE_ALIGNED(8, uint64_t, uOffset);
DECLARE_ALIGNED(8, uint64_t, vOffset);
int32_t lumMmxFilter[4 * MAX_FILTER_SIZE];
int32_t chrMmxFilter[4 * MAX_FILTER_SIZE];
int dstW; ///< Width of destination luma/alpha planes.
DECLARE_ALIGNED(8, uint64_t, esp);
DECLARE_ALIGNED(8, uint64_t, vRounder);
DECLARE_ALIGNED(8, uint64_t, u_temp);
DECLARE_ALIGNED(8, uint64_t, v_temp);
DECLARE_ALIGNED(8, uint64_t, y_temp);
int32_t alpMmxFilter[4 * MAX_FILTER_SIZE];
// alignment of these values is not necessary, but merely here
// to maintain the same offset across x8632 and x86-64. Once we
// use proper offset macros in the asm, they can be removed.
DECLARE_ALIGNED(8, ptrdiff_t, uv_off); ///< offset (in pixels) between u and v planes
DECLARE_ALIGNED(8, ptrdiff_t, uv_offx2); ///< offset (in bytes) between u and v planes
DECLARE_ALIGNED(8, uint16_t, dither16)[8];
DECLARE_ALIGNED(8, uint32_t, dither32)[8];
const uint8_t *chrDither8, *lumDither8;
#if HAVE_ALTIVEC
vector signed short CY;
vector signed short CRV;
vector signed short CBU;
vector signed short CGU;
vector signed short CGV;
vector signed short OY;
vector unsigned short CSHIFT;
vector signed short *vYCoeffsBank, *vCCoeffsBank;
#endif
int use_mmx_vfilter;
/* pre defined color-spaces gamma */
#define XYZ_GAMMA (2.6f)
#define RGB_GAMMA (2.2f)
int16_t *xyzgamma;
int16_t *rgbgamma;
int16_t *xyzgammainv;
int16_t *rgbgammainv;
int16_t xyz2rgb_matrix[3][4];
int16_t rgb2xyz_matrix[3][4];
/* function pointers for swscale() */
yuv2planar1_fn yuv2plane1;
yuv2planarX_fn yuv2planeX;
yuv2interleavedX_fn yuv2nv12cX;
yuv2packed1_fn yuv2packed1;
yuv2packed2_fn yuv2packed2;
yuv2packedX_fn yuv2packedX;
yuv2anyX_fn yuv2anyX;
/// Unscaled conversion of luma plane to YV12 for horizontal scaler.
void (*lumToYV12)(uint8_t *dst, const uint8_t *src, const uint8_t *src2, const uint8_t *src3,
int width, uint32_t *pal);
/// Unscaled conversion of alpha plane to YV12 for horizontal scaler.
void (*alpToYV12)(uint8_t *dst, const uint8_t *src, const uint8_t *src2, const uint8_t *src3,
int width, uint32_t *pal);
/// Unscaled conversion of chroma planes to YV12 for horizontal scaler.
void (*chrToYV12)(uint8_t *dstU, uint8_t *dstV,
const uint8_t *src1, const uint8_t *src2, const uint8_t *src3,
int width, uint32_t *pal);
/**
* Functions to read planar input, such as planar RGB, and convert
* internally to Y/UV/A.
*/
/** @{ */
void (*readLumPlanar)(uint8_t *dst, const uint8_t *src[4], int width, int32_t *rgb2yuv);
void (*readChrPlanar)(uint8_t *dstU, uint8_t *dstV, const uint8_t *src[4],
int width, int32_t *rgb2yuv);
void (*readAlpPlanar)(uint8_t *dst, const uint8_t *src[4], int width, int32_t *rgb2yuv);
/** @} */
/**
* Scale one horizontal line of input data using a bilinear filter
* to produce one line of output data. Compared to SwsContext->hScale(),
* please take note of the following caveats when using these:
* - Scaling is done using only 7bit instead of 14bit coefficients.
* - You can use no more than 5 input pixels to produce 4 output
* pixels. Therefore, this filter should not be used for downscaling
* by more than ~20% in width (because that equals more than 5/4th
* downscaling and thus more than 5 pixels input per 4 pixels output).
* - In general, bilinear filters create artifacts during downscaling
* (even when <20%), because one output pixel will span more than one
* input pixel, and thus some pixels will need edges of both neighbor
* pixels to interpolate the output pixel. Since you can use at most
* two input pixels per output pixel in bilinear scaling, this is
* impossible and thus downscaling by any size will create artifacts.
* To enable this type of scaling, set SWS_FLAG_FAST_BILINEAR
* in SwsContext->flags.
*/
/** @{ */
void (*hyscale_fast)(struct SwsContext *c,
int16_t *dst, int dstWidth,
const uint8_t *src, int srcW, int xInc);
void (*hcscale_fast)(struct SwsContext *c,
int16_t *dst1, int16_t *dst2, int dstWidth,
const uint8_t *src1, const uint8_t *src2,
int srcW, int xInc);
/** @} */
/**
* Scale one horizontal line of input data using a filter over the input
* lines, to produce one (differently sized) line of output data.
*
* @param dst pointer to destination buffer for horizontally scaled
* data. If the number of bits per component of one
* destination pixel (SwsContext->dstBpc) is <= 10, data
* will be 15bpc in 16bits (int16_t) width. Else (i.e.
* SwsContext->dstBpc == 16), data will be 19bpc in
* 32bits (int32_t) width.
* @param dstW width of destination image
* @param src pointer to source data to be scaled. If the number of
* bits per component of a source pixel (SwsContext->srcBpc)
* is 8, this is 8bpc in 8bits (uint8_t) width. Else
* (i.e. SwsContext->dstBpc > 8), this is native depth
* in 16bits (uint16_t) width. In other words, for 9-bit
* YUV input, this is 9bpc, for 10-bit YUV input, this is
* 10bpc, and for 16-bit RGB or YUV, this is 16bpc.
* @param filter filter coefficients to be used per output pixel for
* scaling. This contains 14bpp filtering coefficients.
* Guaranteed to contain dstW * filterSize entries.
* @param filterPos position of the first input pixel to be used for
* each output pixel during scaling. Guaranteed to
* contain dstW entries.
* @param filterSize the number of input coefficients to be used (and
* thus the number of input pixels to be used) for
* creating a single output pixel. Is aligned to 4
* (and input coefficients thus padded with zeroes)
* to simplify creating SIMD code.
*/
/** @{ */
void (*hyScale)(struct SwsContext *c, int16_t *dst, int dstW,
const uint8_t *src, const int16_t *filter,
const int32_t *filterPos, int filterSize);
void (*hcScale)(struct SwsContext *c, int16_t *dst, int dstW,
const uint8_t *src, const int16_t *filter,
const int32_t *filterPos, int filterSize);
/** @} */
/// Color range conversion function for luma plane if needed.
void (*lumConvertRange)(int16_t *dst, int width);
/// Color range conversion function for chroma planes if needed.
void (*chrConvertRange)(int16_t *dst1, int16_t *dst2, int width);
int needs_hcscale; ///< Set if there are chroma planes to be converted.
SwsDither dither;
} SwsContext;

这个结构体的定义确实比较复杂，里面包含了libswscale所需要的全部变量。一一分析这些变量是不太现实的，在后文中会简单分析其中的几个变量。

sws_getContext()

sws_getContext()是初始化SwsContext的函数。sws_getContext()的声明位于libswscale\swscale.h，如下所示。

[cpp] view plaincopy

/**
* Allocate and return an SwsContext. You need it to perform
* scaling/conversion operations using sws_scale().
*
* @param srcW the width of the source image
* @param srcH the height of the source image
* @param srcFormat the source image format
* @param dstW the width of the destination image
* @param dstH the height of the destination image
* @param dstFormat the destination image format
* @param flags specify which algorithm and options to use for rescaling
* @return a pointer to an allocated context, or NULL in case of error
* @note this function is to be removed after a saner alternative is
* written
*/
struct SwsContext *sws_getContext(int srcW, int srcH, enum AVPixelFormat srcFormat,
int dstW, int dstH, enum AVPixelFormat dstFormat,
int flags, SwsFilter *srcFilter,
SwsFilter *dstFilter, const double *param);

该函数包含以下参数：

srcW：源图像的宽
srcH：源图像的高
srcFormat：源图像的像素格式
dstW：目标图像的宽
dstH：目标图像的高
dstFormat：目标图像的像素格式
flags：设定图像拉伸使用的算法

成功执行的话返回生成的SwsContext，否则返回NULL。
sws_getContext()的定义位于libswscale\utils.c，如下所示。

[cpp] view plaincopy

SwsContext *sws_getContext(int srcW, int srcH, enum AVPixelFormat srcFormat,
int dstW, int dstH, enum AVPixelFormat dstFormat,
int flags, SwsFilter *srcFilter,
SwsFilter *dstFilter, const double *param)
{
SwsContext *c;
if (!(c = sws_alloc_context()))
return NULL;
c->flags = flags;
c->srcW = srcW;
c->srcH = srcH;
c->dstW = dstW;
c->dstH = dstH;
c->srcFormat = srcFormat;
c->dstFormat = dstFormat;
if (param) {
c->param[0] = param[0];
c->param[1] = param[1];
}
if (sws_init_context(c, srcFilter, dstFilter) < 0) {
sws_freeContext(c);
return NULL;
}
return c;
}

从sws_getContext()的定义中可以看出，它首先调用了一个函数sws_alloc_context()用于给SwsContext分配内存。然后将传入的源图像，目标图像的宽高，像素格式，以及标志位分别赋值给该SwsContext相应的字段。最后调用一个函数sws_init_context()完成初始化工作。下面我们分别看一下sws_alloc_context()和sws_init_context()这两个函数。

sws_alloc_context()

sws_alloc_context()是FFmpeg的一个API，用于给SwsContext分配内存，它的声明如下所示。

[cpp] view plaincopy

/**
* Allocate an empty SwsContext. This must be filled and passed to
* sws_init_context(). For filling see AVOptions, options.c and
* sws_setColorspaceDetails().
*/
struct SwsContext *sws_alloc_context(void);

sws_alloc_context()的定义位于libswscale\utils.c，如下所示。

[cpp] view plaincopy

SwsContext *sws_alloc_context(void)
{
SwsContext *c = av_mallocz(sizeof(SwsContext));
av_assert0(offsetof(SwsContext, redDither) + DITHER32_INT == offsetof(SwsContext, dither32));
if (c) {
c->av_class = &sws_context_class;
av_opt_set_defaults(c);
}
return c;
}

从代码中可以看出，sws_alloc_context()首先调用av_mallocz()为SwsContext结构体分配了一块内存；然后设置了该结构体的AVClass，并且给该结构体的字段设置了默认值。

sws_init_context()

sws_init_context()的是FFmpeg的一个API，用于初始化SwsContext。

[cpp] view plaincopy

/**
* Initialize the swscaler context sws_context.
*
* @return zero or positive value on success, a negative value on
* error
*/
int sws_init_context(struct SwsContext *sws_context, SwsFilter *srcFilter, SwsFilter *dstFilter);

sws_init_context()的函数定义非常的长，位于libswscale\utils.c，如下所示。

[cpp] view plaincopy

av_cold int sws_init_context(SwsContext *c, SwsFilter *srcFilter,
SwsFilter *dstFilter)
{
int i, j;
int usesVFilter, usesHFilter;
int unscaled;
SwsFilter dummyFilter = { NULL, NULL, NULL, NULL };
int srcW = c->srcW;
int srcH = c->srcH;
int dstW = c->dstW;
int dstH = c->dstH;
int dst_stride = FFALIGN(dstW * sizeof(int16_t) + 66, 16);
int flags, cpu_flags;
enum AVPixelFormat srcFormat = c->srcFormat;
enum AVPixelFormat dstFormat = c->dstFormat;
const AVPixFmtDescriptor *desc_src;
const AVPixFmtDescriptor *desc_dst;
int ret = 0;
//获取
cpu_flags = av_get_cpu_flags();
flags = c->flags;
emms_c();
if (!rgb15to16)
sws_rgb2rgb_init();
//如果输入的宽高和输出的宽高一样，则做特殊处理
unscaled = (srcW == dstW && srcH == dstH);
//如果是JPEG标准（Y取值0-255），则需要设置这两项
c->srcRange |= handle_jpeg(&c->srcFormat);
c->dstRange |= handle_jpeg(&c->dstFormat);
if(srcFormat!=c->srcFormat || dstFormat!=c->dstFormat)
av_log(c, AV_LOG_WARNING, "deprecated pixel format used, make sure you did set range correctly\n");
//设置Colorspace
if (!c->contrast && !c->saturation && !c->dstFormatBpp)
sws_setColorspaceDetails(c, ff_yuv2rgb_coeffs[SWS_CS_DEFAULT], c->srcRange,
ff_yuv2rgb_coeffs[SWS_CS_DEFAULT],
c->dstRange, 0, 1 << 16, 1 << 16);
handle_formats(c);
srcFormat = c->srcFormat;
dstFormat = c->dstFormat;
desc_src = av_pix_fmt_desc_get(srcFormat);
desc_dst = av_pix_fmt_desc_get(dstFormat);
//转换大小端？
if (!(unscaled && sws_isSupportedEndiannessConversion(srcFormat) &&
av_pix_fmt_swap_endianness(srcFormat) == dstFormat)) {
//检查输入格式是否支持
if (!sws_isSupportedInput(srcFormat)) {
av_log(c, AV_LOG_ERROR, "%s is not supported as input pixel format\n",
av_get_pix_fmt_name(srcFormat));
return AVERROR(EINVAL);
}
//检查输出格式是否支持
if (!sws_isSupportedOutput(dstFormat)) {
av_log(c, AV_LOG_ERROR, "%s is not supported as output pixel format\n",
av_get_pix_fmt_name(dstFormat));
return AVERROR(EINVAL);
}
}
//检查拉伸的方法
i = flags & (SWS_POINT |
SWS_AREA |
SWS_BILINEAR |
SWS_FAST_BILINEAR |
SWS_BICUBIC |
SWS_X |
SWS_GAUSS |
SWS_LANCZOS |
SWS_SINC |
SWS_SPLINE |
SWS_BICUBLIN);
/* provide a default scaler if not set by caller */
//如果没有指定，就使用默认的
if (!i) {
if (dstW < srcW && dstH < srcH)
flags |= SWS_BICUBIC;
else if (dstW > srcW && dstH > srcH)
flags |= SWS_BICUBIC;
else
flags |= SWS_BICUBIC;
c->flags = flags;
} else if (i & (i - 1)) {
av_log(c, AV_LOG_ERROR,
"Exactly one scaler algorithm must be chosen, got %X\n", i);
return AVERROR(EINVAL);
}
/* sanity check */
//检查宽高参数
if (srcW < 1 || srcH < 1 || dstW < 1 || dstH < 1) {
/* FIXME check if these are enough and try to lower them after
* fixing the relevant parts of the code */
av_log(c, AV_LOG_ERROR, "%dx%d -> %dx%d is invalid scaling dimension\n",
srcW, srcH, dstW, dstH);
return AVERROR(EINVAL);
}
if (!dstFilter)
dstFilter = &dummyFilter;
if (!srcFilter)
srcFilter = &dummyFilter;
c->lumXInc = (((int64_t)srcW << 16) + (dstW >> 1)) / dstW;
c->lumYInc = (((int64_t)srcH << 16) + (dstH >> 1)) / dstH;
c->dstFormatBpp = av_get_bits_per_pixel(desc_dst);
c->srcFormatBpp = av_get_bits_per_pixel(desc_src);
c->vRounder = 4 * 0x0001000100010001ULL;
usesVFilter = (srcFilter->lumV && srcFilter->lumV->length > 1) ||
(srcFilter->chrV && srcFilter->chrV->length > 1) ||
(dstFilter->lumV && dstFilter->lumV->length > 1) ||
(dstFilter->chrV && dstFilter->chrV->length > 1);
usesHFilter = (srcFilter->lumH && srcFilter->lumH->length > 1) ||
(srcFilter->chrH && srcFilter->chrH->length > 1) ||
(dstFilter->lumH && dstFilter->lumH->length > 1) ||
(dstFilter->chrH && dstFilter->chrH->length > 1);
av_pix_fmt_get_chroma_sub_sample(srcFormat, &c->chrSrcHSubSample, &c->chrSrcVSubSample);
av_pix_fmt_get_chroma_sub_sample(dstFormat, &c->chrDstHSubSample, &c->chrDstVSubSample);
if (isAnyRGB(dstFormat) && !(flags&SWS_FULL_CHR_H_INT)) {
if (dstW&1) {
av_log(c, AV_LOG_DEBUG, "Forcing full internal H chroma due to odd output size\n");
flags |= SWS_FULL_CHR_H_INT;
c->flags = flags;
}
if ( c->chrSrcHSubSample == 0
&& c->chrSrcVSubSample == 0
&& c->dither != SWS_DITHER_BAYER //SWS_FULL_CHR_H_INT is currently not supported with SWS_DITHER_BAYER
&& !(c->flags & SWS_FAST_BILINEAR)
) {
av_log(c, AV_LOG_DEBUG, "Forcing full internal H chroma due to input having non subsampled chroma\n");
flags |= SWS_FULL_CHR_H_INT;
c->flags = flags;
}
}
if (c->dither == SWS_DITHER_AUTO) {
if (flags & SWS_ERROR_DIFFUSION)
c->dither = SWS_DITHER_ED;
}
if(dstFormat == AV_PIX_FMT_BGR4_BYTE ||
dstFormat == AV_PIX_FMT_RGB4_BYTE ||
dstFormat == AV_PIX_FMT_BGR8 ||
dstFormat == AV_PIX_FMT_RGB8) {
if (c->dither == SWS_DITHER_AUTO)
c->dither = (flags & SWS_FULL_CHR_H_INT) ? SWS_DITHER_ED : SWS_DITHER_BAYER;
if (!(flags & SWS_FULL_CHR_H_INT)) {
if (c->dither == SWS_DITHER_ED || c->dither == SWS_DITHER_A_DITHER || c->dither == SWS_DITHER_X_DITHER) {
av_log(c, AV_LOG_DEBUG,
"Desired dithering only supported in full chroma interpolation for destination format '%s'\n",
av_get_pix_fmt_name(dstFormat));
flags |= SWS_FULL_CHR_H_INT;
c->flags = flags;
}
}
if (flags & SWS_FULL_CHR_H_INT) {
if (c->dither == SWS_DITHER_BAYER) {
av_log(c, AV_LOG_DEBUG,
"Ordered dither is not supported in full chroma interpolation for destination format '%s'\n",
av_get_pix_fmt_name(dstFormat));
c->dither = SWS_DITHER_ED;
}
}
}
if (isPlanarRGB(dstFormat)) {
if (!(flags & SWS_FULL_CHR_H_INT)) {
av_log(c, AV_LOG_DEBUG,
"%s output is not supported with half chroma resolution, switching to full\n",
av_get_pix_fmt_name(dstFormat));
flags |= SWS_FULL_CHR_H_INT;
c->flags = flags;
}
}
/* reuse chroma for 2 pixels RGB/BGR unless user wants full
* chroma interpolation */
if (flags & SWS_FULL_CHR_H_INT &&
isAnyRGB(dstFormat) &&
!isPlanarRGB(dstFormat) &&
dstFormat != AV_PIX_FMT_RGBA &&
dstFormat != AV_PIX_FMT_ARGB &&
dstFormat != AV_PIX_FMT_BGRA &&
dstFormat != AV_PIX_FMT_ABGR &&
dstFormat != AV_PIX_FMT_RGB24 &&
dstFormat != AV_PIX_FMT_BGR24 &&
dstFormat != AV_PIX_FMT_BGR4_BYTE &&
dstFormat != AV_PIX_FMT_RGB4_BYTE &&
dstFormat != AV_PIX_FMT_BGR8 &&
dstFormat != AV_PIX_FMT_RGB8
) {
av_log(c, AV_LOG_WARNING,
"full chroma interpolation for destination format '%s' not yet implemented\n",
av_get_pix_fmt_name(dstFormat));
flags &= ~SWS_FULL_CHR_H_INT;
c->flags = flags;
}
if (isAnyRGB(dstFormat) && !(flags & SWS_FULL_CHR_H_INT))
c->chrDstHSubSample = 1;
// drop some chroma lines if the user wants it
c->vChrDrop = (flags & SWS_SRC_V_CHR_DROP_MASK) >>
SWS_SRC_V_CHR_DROP_SHIFT;
c->chrSrcVSubSample += c->vChrDrop;
/* drop every other pixel for chroma calculation unless user
* wants full chroma */
if (isAnyRGB(srcFormat) && !(flags & SWS_FULL_CHR_H_INP) &&
srcFormat != AV_PIX_FMT_RGB8 && srcFormat != AV_PIX_FMT_BGR8 &&
srcFormat != AV_PIX_FMT_RGB4 && srcFormat != AV_PIX_FMT_BGR4 &&
srcFormat != AV_PIX_FMT_RGB4_BYTE && srcFormat != AV_PIX_FMT_BGR4_BYTE &&
srcFormat != AV_PIX_FMT_GBRP9BE && srcFormat != AV_PIX_FMT_GBRP9LE &&
srcFormat != AV_PIX_FMT_GBRP10BE && srcFormat != AV_PIX_FMT_GBRP10LE &&
srcFormat != AV_PIX_FMT_GBRP12BE && srcFormat != AV_PIX_FMT_GBRP12LE &&
srcFormat != AV_PIX_FMT_GBRP14BE && srcFormat != AV_PIX_FMT_GBRP14LE &&
srcFormat != AV_PIX_FMT_GBRP16BE && srcFormat != AV_PIX_FMT_GBRP16LE &&
((dstW >> c->chrDstHSubSample) <= (srcW >> 1) ||
(flags & SWS_FAST_BILINEAR)))
c->chrSrcHSubSample = 1;
// Note the FF_CEIL_RSHIFT is so that we always round toward +inf.
c->chrSrcW = FF_CEIL_RSHIFT(srcW, c->chrSrcHSubSample);
c->chrSrcH = FF_CEIL_RSHIFT(srcH, c->chrSrcVSubSample);
c->chrDstW = FF_CEIL_RSHIFT(dstW, c->chrDstHSubSample);
c->chrDstH = FF_CEIL_RSHIFT(dstH, c->chrDstVSubSample);
FF_ALLOC_OR_GOTO(c, c->formatConvBuffer, FFALIGN(srcW*2+78, 16) * 2, fail);
c->srcBpc = 1 + desc_src->comp[0].depth_minus1;
if (c->srcBpc < 8)
c->srcBpc = 8;
c->dstBpc = 1 + desc_dst->comp[0].depth_minus1;
if (c->dstBpc < 8)
c->dstBpc = 8;
if (isAnyRGB(srcFormat) || srcFormat == AV_PIX_FMT_PAL8)
c->srcBpc = 16;
if (c->dstBpc == 16)
dst_stride <<= 1;
if (INLINE_MMXEXT(cpu_flags) && c->srcBpc == 8 && c->dstBpc <= 14) {
c->canMMXEXTBeUsed = dstW >= srcW && (dstW & 31) == 0 &&
c->chrDstW >= c->chrSrcW &&
(srcW & 15) == 0;
if (!c->canMMXEXTBeUsed && dstW >= srcW && c->chrDstW >= c->chrSrcW && (srcW & 15) == 0
&& (flags & SWS_FAST_BILINEAR)) {
if (flags & SWS_PRINT_INFO)
av_log(c, AV_LOG_INFO,
"output width is not a multiple of 32 -> no MMXEXT scaler\n");
}
if (usesHFilter || isNBPS(c->srcFormat) || is16BPS(c->srcFormat) || isAnyRGB(c->srcFormat))
c->canMMXEXTBeUsed = 0;
} else
c->canMMXEXTBeUsed = 0;
c->chrXInc = (((int64_t)c->chrSrcW << 16) + (c->chrDstW >> 1)) / c->chrDstW;
c->chrYInc = (((int64_t)c->chrSrcH << 16) + (c->chrDstH >> 1)) / c->chrDstH;
/* Match pixel 0 of the src to pixel 0 of dst and match pixel n-2 of src
* to pixel n-2 of dst, but only for the FAST_BILINEAR mode otherwise do
* correct scaling.
* n-2 is the last chrominance sample available.
* This is not perfect, but no one should notice the difference, the more
* correct variant would be like the vertical one, but that would require
* some special code for the first and last pixel */
if (flags & SWS_FAST_BILINEAR) {
if (c->canMMXEXTBeUsed) {
c->lumXInc += 20;
c->chrXInc += 20;
}
// we don't use the x86 asm scaler if MMX is available
else if (INLINE_MMX(cpu_flags) && c->dstBpc <= 14) {
c->lumXInc = ((int64_t)(srcW - 2) << 16) / (dstW - 2) - 20;
c->chrXInc = ((int64_t)(c->chrSrcW - 2) << 16) / (c->chrDstW - 2) - 20;
}
}
if (isBayer(srcFormat)) {
if (!unscaled ||
(dstFormat != AV_PIX_FMT_RGB24 && dstFormat != AV_PIX_FMT_YUV420P)) {
enum AVPixelFormat tmpFormat = AV_PIX_FMT_RGB24;
ret = av_image_alloc(c->cascaded_tmp, c->cascaded_tmpStride,
srcW, srcH, tmpFormat, 64);
if (ret < 0)
return ret;
c->cascaded_context[0] = sws_getContext(srcW, srcH, srcFormat,
srcW, srcH, tmpFormat,
flags, srcFilter, NULL, c->param);
if (!c->cascaded_context[0])
return -1;
c->cascaded_context[1] = sws_getContext(srcW, srcH, tmpFormat,
dstW, dstH, dstFormat,
flags, NULL, dstFilter, c->param);
if (!c->cascaded_context[1])
return -1;
return 0;
}
}
#define USE_MMAP (HAVE_MMAP && HAVE_MPROTECT && defined MAP_ANONYMOUS)
/* precalculate horizontal scaler filter coefficients */
{
#if HAVE_MMXEXT_INLINE
// can't downscale !!!
if (c->canMMXEXTBeUsed && (flags & SWS_FAST_BILINEAR)) {
c->lumMmxextFilterCodeSize = ff_init_hscaler_mmxext(dstW, c->lumXInc, NULL,
NULL, NULL, 8);
c->chrMmxextFilterCodeSize = ff_init_hscaler_mmxext(c->chrDstW, c->chrXInc,
NULL, NULL, NULL, 4);
#if USE_MMAP
c->lumMmxextFilterCode = mmap(NULL, c->lumMmxextFilterCodeSize,
PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS,
-1, 0);
c->chrMmxextFilterCode = mmap(NULL, c->chrMmxextFilterCodeSize,
PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS,
-1, 0);
#elif HAVE_VIRTUALALLOC
c->lumMmxextFilterCode = VirtualAlloc(NULL,
c->lumMmxextFilterCodeSize,
MEM_COMMIT,
PAGE_EXECUTE_READWRITE);
c->chrMmxextFilterCode = VirtualAlloc(NULL,
c->chrMmxextFilterCodeSize,
MEM_COMMIT,
PAGE_EXECUTE_READWRITE);
#else
c->lumMmxextFilterCode = av_malloc(c->lumMmxextFilterCodeSize);
c->chrMmxextFilterCode = av_malloc(c->chrMmxextFilterCodeSize);
#endif
#ifdef MAP_ANONYMOUS
if (c->lumMmxextFilterCode == MAP_FAILED || c->chrMmxextFilterCode == MAP_FAILED)
#else
if (!c->lumMmxextFilterCode || !c->chrMmxextFilterCode)
#endif
{
av_log(c, AV_LOG_ERROR, "Failed to allocate MMX2FilterCode\n");
return AVERROR(ENOMEM);
}
FF_ALLOCZ_OR_GOTO(c, c->hLumFilter, (dstW / 8 + 8) * sizeof(int16_t), fail);
FF_ALLOCZ_OR_GOTO(c, c->hChrFilter, (c->chrDstW / 4 + 8) * sizeof(int16_t), fail);
FF_ALLOCZ_OR_GOTO(c, c->hLumFilterPos, (dstW / 2 / 8 + 8) * sizeof(int32_t), fail);
FF_ALLOCZ_OR_GOTO(c, c->hChrFilterPos, (c->chrDstW / 2 / 4 + 8) * sizeof(int32_t), fail);
ff_init_hscaler_mmxext( dstW, c->lumXInc, c->lumMmxextFilterCode,
c->hLumFilter, (uint32_t*)c->hLumFilterPos, 8);
ff_init_hscaler_mmxext(c->chrDstW, c->chrXInc, c->chrMmxextFilterCode,
c->hChrFilter, (uint32_t*)c->hChrFilterPos, 4);
#if USE_MMAP
if ( mprotect(c->lumMmxextFilterCode, c->lumMmxextFilterCodeSize, PROT_EXEC | PROT_READ) == -1
|| mprotect(c->chrMmxextFilterCode, c->chrMmxextFilterCodeSize, PROT_EXEC | PROT_READ) == -1) {
av_log(c, AV_LOG_ERROR, "mprotect failed, cannot use fast bilinear scaler\n");
goto fail;
}
#endif
} else
#endif /* HAVE_MMXEXT_INLINE */
{
const int filterAlign = X86_MMX(cpu_flags) ? 4 :
PPC_ALTIVEC(cpu_flags) ? 8 : 1;
if ((ret = initFilter(&c->hLumFilter, &c->hLumFilterPos,
&c->hLumFilterSize, c->lumXInc,
srcW, dstW, filterAlign, 1 << 14,
(flags & SWS_BICUBLIN) ? (flags | SWS_BICUBIC) : flags,
cpu_flags, srcFilter->lumH, dstFilter->lumH,
c->param,
get_local_pos(c, 0, 0, 0),
get_local_pos(c, 0, 0, 0))) < 0)
goto fail;
if ((ret = initFilter(&c->hChrFilter, &c->hChrFilterPos,
&c->hChrFilterSize, c->chrXInc,
c->chrSrcW, c->chrDstW, filterAlign, 1 << 14,
(flags & SWS_BICUBLIN) ? (flags | SWS_BILINEAR) : flags,
cpu_flags, srcFilter->chrH, dstFilter->chrH,
c->param,
get_local_pos(c, c->chrSrcHSubSample, c->src_h_chr_pos, 0),
get_local_pos(c, c->chrDstHSubSample, c->dst_h_chr_pos, 0))) < 0)
goto fail;
}
} // initialize horizontal stuff
/* precalculate vertical scaler filter coefficients */
{
const int filterAlign = X86_MMX(cpu_flags) ? 2 :
PPC_ALTIVEC(cpu_flags) ? 8 : 1;
if ((ret = initFilter(&c->vLumFilter, &c->vLumFilterPos, &c->vLumFilterSize,
c->lumYInc, srcH, dstH, filterAlign, (1 << 12),
(flags & SWS_BICUBLIN) ? (flags | SWS_BICUBIC) : flags,
cpu_flags, srcFilter->lumV, dstFilter->lumV,
c->param,
get_local_pos(c, 0, 0, 1),
get_local_pos(c, 0, 0, 1))) < 0)
goto fail;
if ((ret = initFilter(&c->vChrFilter, &c->vChrFilterPos, &c->vChrFilterSize,
c->chrYInc, c->chrSrcH, c->chrDstH,
filterAlign, (1 << 12),
(flags & SWS_BICUBLIN) ? (flags | SWS_BILINEAR) : flags,
cpu_flags, srcFilter->chrV, dstFilter->chrV,
c->param,
get_local_pos(c, c->chrSrcVSubSample, c->src_v_chr_pos, 1),
get_local_pos(c, c->chrDstVSubSample, c->dst_v_chr_pos, 1))) < 0)
goto fail;
#if HAVE_ALTIVEC
FF_ALLOC_OR_GOTO(c, c->vYCoeffsBank, sizeof(vector signed short) * c->vLumFilterSize * c->dstH, fail);
FF_ALLOC_OR_GOTO(c, c->vCCoeffsBank, sizeof(vector signed short) * c->vChrFilterSize * c->chrDstH, fail);
for (i = 0; i < c->vLumFilterSize * c->dstH; i++) {
int j;
short *p = (short *)&c->vYCoeffsBank[i];
for (j = 0; j < 8; j++)
p[j] = c->vLumFilter[i];
}
for (i = 0; i < c->vChrFilterSize * c->chrDstH; i++) {
int j;
short *p = (short *)&c->vCCoeffsBank[i];
for (j = 0; j < 8; j++)
p[j] = c->vChrFilter[i];
}
#endif
}
// calculate buffer sizes so that they won't run out while handling these damn slices
c->vLumBufSize = c->vLumFilterSize;
c->vChrBufSize = c->vChrFilterSize;
for (i = 0; i < dstH; i++) {
int chrI = (int64_t)i * c->chrDstH / dstH;
int nextSlice = FFMAX(c->vLumFilterPos[i] + c->vLumFilterSize - 1,
((c->vChrFilterPos[chrI] + c->vChrFilterSize - 1)
<< c->chrSrcVSubSample));
nextSlice >>= c->chrSrcVSubSample;
nextSlice <<= c->chrSrcVSubSample;
if (c->vLumFilterPos[i] + c->vLumBufSize < nextSlice)
c->vLumBufSize = nextSlice - c->vLumFilterPos[i];
if (c->vChrFilterPos[chrI] + c->vChrBufSize <
(nextSlice >> c->chrSrcVSubSample))
c->vChrBufSize = (nextSlice >> c->chrSrcVSubSample) -
c->vChrFilterPos[chrI];
}
for (i = 0; i < 4; i++)
FF_ALLOCZ_OR_GOTO(c, c->dither_error[i], (c->dstW+2) * sizeof(int), fail);
/* Allocate pixbufs (we use dynamic allocation because otherwise we would
* need to allocate several megabytes to handle all possible cases) */
FF_ALLOC_OR_GOTO(c, c->lumPixBuf, c->vLumBufSize * 3 * sizeof(int16_t *), fail);
FF_ALLOC_OR_GOTO(c, c->chrUPixBuf, c->vChrBufSize * 3 * sizeof(int16_t *), fail);
FF_ALLOC_OR_GOTO(c, c->chrVPixBuf, c->vChrBufSize * 3 * sizeof(int16_t *), fail);
if (CONFIG_SWSCALE_ALPHA && isALPHA(c->srcFormat) && isALPHA(c->dstFormat))
FF_ALLOCZ_OR_GOTO(c, c->alpPixBuf, c->vLumBufSize * 3 * sizeof(int16_t *), fail);
/* Note we need at least one pixel more at the end because of the MMX code
* (just in case someone wants to replace the 4000/8000). */
/* align at 16 bytes for AltiVec */
for (i = 0; i < c->vLumBufSize; i++) {
FF_ALLOCZ_OR_GOTO(c, c->lumPixBuf[i + c->vLumBufSize],
dst_stride + 16, fail);
c->lumPixBuf[i] = c->lumPixBuf[i + c->vLumBufSize];
}
// 64 / c->scalingBpp is the same as 16 / sizeof(scaling_intermediate)
c->uv_off = (dst_stride>>1) + 64 / (c->dstBpc &~ 7);
c->uv_offx2 = dst_stride + 16;
for (i = 0; i < c->vChrBufSize; i++) {
FF_ALLOC_OR_GOTO(c, c->chrUPixBuf[i + c->vChrBufSize],
dst_stride * 2 + 32, fail);
c->chrUPixBuf[i] = c->chrUPixBuf[i + c->vChrBufSize];
c->chrVPixBuf[i] = c->chrVPixBuf[i + c->vChrBufSize]
= c->chrUPixBuf[i] + (dst_stride >> 1) + 8;
}
if (CONFIG_SWSCALE_ALPHA && c->alpPixBuf)
for (i = 0; i < c->vLumBufSize; i++) {
FF_ALLOCZ_OR_GOTO(c, c->alpPixBuf[i + c->vLumBufSize],
dst_stride + 16, fail);
c->alpPixBuf[i] = c->alpPixBuf[i + c->vLumBufSize];
}
// try to avoid drawing green stuff between the right end and the stride end
for (i = 0; i < c->vChrBufSize; i++)
if(desc_dst->comp[0].depth_minus1 == 15){
av_assert0(c->dstBpc > 14);
for(j=0; j<dst_stride/2+1; j++)
((int32_t*)(c->chrUPixBuf[i]))[j] = 1<<18;
} else
for(j=0; j<dst_stride+1; j++)
((int16_t*)(c->chrUPixBuf[i]))[j] = 1<<14;
av_assert0(c->chrDstH <= dstH);
//是否要输出
if (flags & SWS_PRINT_INFO) {
const char *scaler = NULL, *cpucaps;
for (i = 0; i < FF_ARRAY_ELEMS(scale_algorithms); i++) {
if (flags & scale_algorithms[i].flag) {
scaler = scale_algorithms[i].description;
break;
}
}
if (!scaler)
scaler = "ehh flags invalid?!";
av_log(c, AV_LOG_INFO, "%s scaler, from %s to %s%s ",
scaler,
av_get_pix_fmt_name(srcFormat),
#ifdef DITHER1XBPP
dstFormat == AV_PIX_FMT_BGR555 || dstFormat == AV_PIX_FMT_BGR565 ||
dstFormat == AV_PIX_FMT_RGB444BE || dstFormat == AV_PIX_FMT_RGB444LE ||
dstFormat == AV_PIX_FMT_BGR444BE || dstFormat == AV_PIX_FMT_BGR444LE ?
"dithered " : "",
#else
"",
#endif
av_get_pix_fmt_name(dstFormat));
if (INLINE_MMXEXT(cpu_flags))
cpucaps = "MMXEXT";
else if (INLINE_AMD3DNOW(cpu_flags))
cpucaps = "3DNOW";
else if (INLINE_MMX(cpu_flags))
cpucaps = "MMX";
else if (PPC_ALTIVEC(cpu_flags))
cpucaps = "AltiVec";
else
cpucaps = "C";
av_log(c, AV_LOG_INFO, "using %s\n", cpucaps);
av_log(c, AV_LOG_VERBOSE, "%dx%d -> %dx%d\n", srcW, srcH, dstW, dstH);
av_log(c, AV_LOG_DEBUG,
"lum srcW=%d srcH=%d dstW=%d dstH=%d xInc=%d yInc=%d\n",
c->srcW, c->srcH, c->dstW, c->dstH, c->lumXInc, c->lumYInc);
av_log(c, AV_LOG_DEBUG,
"chr srcW=%d srcH=%d dstW=%d dstH=%d xInc=%d yInc=%d\n",
c->chrSrcW, c->chrSrcH, c->chrDstW, c->chrDstH,
c->chrXInc, c->chrYInc);
}
/* unscaled special cases */
//不拉伸的情况
if (unscaled && !usesHFilter && !usesVFilter &&
(c->srcRange == c->dstRange || isAnyRGB(dstFormat))) {
//不许拉伸的情况下，初始化相应的函数
ff_get_unscaled_swscale(c);
if (c->swscale) {
if (flags & SWS_PRINT_INFO)
av_log(c, AV_LOG_INFO,
"using unscaled %s -> %s special converter\n",
av_get_pix_fmt_name(srcFormat), av_get_pix_fmt_name(dstFormat));
return 0;
}
}
//关键：设置SwsContext中的swscale()指针
c->swscale = ff_getSwsFunc(c);
return 0;
fail: // FIXME replace things by appropriate error codes
if (ret == RETCODE_USE_CASCADE) {
int tmpW = sqrt(srcW * (int64_t)dstW);
int tmpH = sqrt(srcH * (int64_t)dstH);
enum AVPixelFormat tmpFormat = AV_PIX_FMT_YUV420P;
if (srcW*(int64_t)srcH <= 4LL*dstW*dstH)
return AVERROR(EINVAL);
ret = av_image_alloc(c->cascaded_tmp, c->cascaded_tmpStride,
tmpW, tmpH, tmpFormat, 64);
if (ret < 0)
return ret;
c->cascaded_context[0] = sws_getContext(srcW, srcH, srcFormat,
tmpW, tmpH, tmpFormat,
flags, srcFilter, NULL, c->param);
if (!c->cascaded_context[0])
return -1;
c->cascaded_context[1] = sws_getContext(tmpW, tmpH, tmpFormat,
dstW, dstH, dstFormat,
flags, NULL, dstFilter, c->param);
if (!c->cascaded_context[1])
return -1;
return 0;
}
return -1;
}

sws_init_context()除了对SwsContext中的各种变量进行赋值之外，主要按照顺序完成了以下一些工作：

1. 通过sws_rgb2rgb_init()初始化RGB转RGB（或者YUV转YUV）的函数（注意不包含RGB与YUV相互转换的函数）。
2. 通过判断输入输出图像的宽高来判断图像是否需要拉伸。如果图像需要拉伸，那么unscaled变量会被标记为1。
3. 通过sws_setColorspaceDetails()初始化颜色空间。
4. 一些输入参数的检测。例如：如果没有设置图像拉伸方法的话，默认设置为SWS_BICUBIC；如果输入和输出图像的宽高小于等于0的话，也会返回错误信息。
5. 初始化Filter。这一步根据拉伸方法的不同，初始化不同的Filter。
6. 如果flags中设置了“打印信息”选项SWS_PRINT_INFO，则输出信息。
7. 如果不需要拉伸的话，调用ff_get_unscaled_swscale()将特定的像素转换函数的指针赋值给SwsContext中的swscale指针。
8. 如果需要拉伸的话，调用ff_getSwsFunc()将通用的swscale()赋值给SwsContext中的swscale指针（这个地方有点绕，但是确实是这样的）。

下面分别记录一下上述步骤的实现。

1.初始化RGB转RGB（或者YUV转YUV）的函数。注意这部分函数不包含RGB与YUV相互转换的函数。

sws_rgb2rgb_init()

sws_rgb2rgb_init()的定义位于libswscale\rgb2rgb.c，如下所示。

[cpp] view plaincopy

av_cold void sws_rgb2rgb_init(void){
rgb2rgb_init_c();
if (ARCH_X86)
rgb2rgb_init_x86();
}

从sws_rgb2rgb_init()代码中可以看出，有两个初始化函数：rgb2rgb_init_c()是初始化C语言版本的RGB互转（或者YUV互转）的函数，rgb2rgb_init_x86()则是初始化X86汇编版本的RGB互转的函数。
PS：在libswscale中有一点需要注意：很多的函数名称中包含类似“_c”这样的字符串，代表了该函数是C语言写的。与之对应的还有其它标记，比如“_mmx”，“sse2”等。

rgb2rgb_init_c()

首先来看一下C语言版本的RGB互转函数的初始化函数rgb2rgb_init_c()，定义位于libswscale\rgb2rgb_template.c，如下所示。

[cpp] view plaincopy

static av_cold void rgb2rgb_init_c(void)
{
rgb15to16 = rgb15to16_c;
rgb15tobgr24 = rgb15tobgr24_c;
rgb15to32 = rgb15to32_c;
rgb16tobgr24 = rgb16tobgr24_c;
rgb16to32 = rgb16to32_c;
rgb16to15 = rgb16to15_c;
rgb24tobgr16 = rgb24tobgr16_c;
rgb24tobgr15 = rgb24tobgr15_c;
rgb24tobgr32 = rgb24tobgr32_c;
rgb32to16 = rgb32to16_c;
rgb32to15 = rgb32to15_c;
rgb32tobgr24 = rgb32tobgr24_c;
rgb24to15 = rgb24to15_c;
rgb24to16 = rgb24to16_c;
rgb24tobgr24 = rgb24tobgr24_c;
shuffle_bytes_2103 = shuffle_bytes_2103_c;
rgb32tobgr16 = rgb32tobgr16_c;
rgb32tobgr15 = rgb32tobgr15_c;
yv12toyuy2 = yv12toyuy2_c;
yv12touyvy = yv12touyvy_c;
yuv422ptoyuy2 = yuv422ptoyuy2_c;
yuv422ptouyvy = yuv422ptouyvy_c;
yuy2toyv12 = yuy2toyv12_c;
planar2x = planar2x_c;
ff_rgb24toyv12 = ff_rgb24toyv12_c;
interleaveBytes = interleaveBytes_c;
deinterleaveBytes = deinterleaveBytes_c;
vu9_to_vu12 = vu9_to_vu12_c;
yvu9_to_yuy2 = yvu9_to_yuy2_c;
uyvytoyuv420 = uyvytoyuv420_c;
uyvytoyuv422 = uyvytoyuv422_c;
yuyvtoyuv420 = yuyvtoyuv420_c;
yuyvtoyuv422 = yuyvtoyuv422_c;
}

可以看出rgb2rgb_init_c()执行后，会把C语言版本的图像格式转换函数赋值给系统的函数指针。

下面我们选择几个函数看一下这些转换函数的定义。

rgb24tobgr24_c()

rgb24tobgr24_c()完成了RGB24向BGR24格式的转换。函数的定义如下所示。从代码中可以看出，该函数实现了“R”与“B”之间位置的对调，从而完成了这两种格式之间的转换。

[cpp] view plaincopy

static inline void rgb24tobgr24_c(const uint8_t *src, uint8_t *dst, int src_size)
{
unsigned i;
for (i = 0; i < src_size; i += 3) {
register uint8_t x = src[i + 2];
dst[i + 1] = src[i + 1];
dst[i + 2] = src[i + 0];
dst[i + 0] = x;
}
}

rgb24to16_c()

rgb24to16_c()完成了RGB24向RGB16像素格式的转换。函数的定义如下所示。

[cpp] view plaincopy

static inline void rgb24to16_c(const uint8_t *src, uint8_t *dst, int src_size)
{
uint16_t *d = (uint16_t *)dst;
const uint8_t *s = src;
const uint8_t *end = s + src_size;
while (s < end) {
const int r = *s++;
const int g = *s++;
const int b = *s++;
*d++ = (b >> 3) | ((g & 0xFC) << 3) | ((r & 0xF8) << 8);
}
}

yuyvtoyuv422_c()

yuyvtoyuv422_c()完成了YUYV向YUV422像素格式的转换。函数的定义如下所示。

[cpp] view plaincopy

static void yuyvtoyuv422_c(uint8_t *ydst, uint8_t *udst, uint8_t *vdst,
const uint8_t *src, int width, int height,
int lumStride, int chromStride, int srcStride)
{
int y;
const int chromWidth = FF_CEIL_RSHIFT(width, 1);
for (y = 0; y < height; y++) {
extract_even_c(src, ydst, width);
extract_odd2_c(src, udst, vdst, chromWidth);
src += srcStride;
ydst += lumStride;
udst += chromStride;
vdst += chromStride;
}
}

该函数将YUYV像素数据分离成为Y，U，V三个分量的像素数据。其中extract_even_c()用于获取一行像素中序数为偶数的像素，对应提取了YUYV像素格式中的“Y”。extract_odd2_c()用于获取一行像素中序数为奇数的像素，并且把这些像素值再次按照奇偶的不同，存储于两个数组中。对应提取了YUYV像素格式中的“U”和“V”。
extract_even_c()定义如下所示。

[cpp] view plaincopy

static void extract_even_c(const uint8_t *src, uint8_t *dst, int count)
{
dst += count;
src += count * 2;
count = -count;
while (count < 0) {
dst[count] = src[2 * count];
count++;
}
}

extract_odd2_c()定义如下所示。

[cpp] view plaincopy

static void extract_even2_c(const uint8_t *src, uint8_t *dst0, uint8_t *dst1,
int count)
{
dst0 += count;
dst1 += count;
src += count * 4;
count = -count;
while (count < 0) {
dst0[count] = src[4 * count + 0];
dst1[count] = src[4 * count + 2];
count++;
}
}

rgb2rgb_init_x86()

rgb2rgb_init_x86()用于初始化基于X86汇编语言的RGB互转的代码。由于对汇编不是很熟，不再作详细分析，出于和rgb2rgb_init_c()相对比的目的，列出它的代码。它的代码位于libswscale\x86\rgb2rgb.c，如下所示。

PS：所有和汇编有关的代码都位于libswscale目录的x86子目录下。

[cpp] view plaincopy

av_cold void rgb2rgb_init_x86(void)
{
#if HAVE_INLINE_ASM
int cpu_flags = av_get_cpu_flags();
if (INLINE_MMX(cpu_flags))
rgb2rgb_init_mmx();
if (INLINE_AMD3DNOW(cpu_flags))
rgb2rgb_init_3dnow();
if (INLINE_MMXEXT(cpu_flags))
rgb2rgb_init_mmxext();
if (INLINE_SSE2(cpu_flags))
rgb2rgb_init_sse2();
if (INLINE_AVX(cpu_flags))
rgb2rgb_init_avx();
#endif /* HAVE_INLINE_ASM */
}

可以看出，rgb2rgb_init_x86()首先调用了av_get_cpu_flags()获取CPU支持的特性，根据特性调用rgb2rgb_init_mmx()，rgb2rgb_init_3dnow()，rgb2rgb_init_mmxext()，rgb2rgb_init_sse2()，rgb2rgb_init_avx()等函数。

2.判断图像是否需要拉伸。

这一步主要通过比较输入图像和输出图像的宽高实现。系统使用一个unscaled变量记录图像是否需要拉伸，如下所示。

[cpp] view plaincopy

unscaled = (srcW == dstW && srcH == dstH);

3.初始化颜色空间。

初始化颜色空间通过函数sws_setColorspaceDetails()完成。sws_setColorspaceDetails()是FFmpeg的一个API函数，它的声明如下所示：

[cpp] view plaincopy

/**
* @param dstRange flag indicating the while-black range of the output (1=jpeg / 0=mpeg)
* @param srcRange flag indicating the while-black range of the input (1=jpeg / 0=mpeg)
* @param table the yuv2rgb coefficients describing the output yuv space, normally ff_yuv2rgb_coeffs[x]
* @param inv_table the yuv2rgb coefficients describing the input yuv space, normally ff_yuv2rgb_coeffs[x]
* @param brightness 16.16 fixed point brightness correction
* @param contrast 16.16 fixed point contrast correction
* @param saturation 16.16 fixed point saturation correction
* @return -1 if not supported
*/
int sws_setColorspaceDetails(struct SwsContext *c, const int inv_table[4],
int srcRange, const int table[4], int dstRange,
int brightness, int contrast, int saturation);

简单解释一下几个参数的含义：

c：需要设定的SwsContext。
inv_table：描述输出YUV颜色空间的参数表。
srcRange：输入图像的取值范围（“1”代表JPEG标准，取值范围是0-255；“0”代表MPEG标准，取值范围是16-235）。
table：描述输入YUV颜色空间的参数表。
dstRange：输出图像的取值范围。
brightness：未研究。
contrast：未研究。
saturation：未研究。

如果返回-1代表设置不成功。
其中描述颜色空间的参数表可以通过sws_getCoefficients()获取。该函数在后文中再详细记录。
sws_setColorspaceDetails()的定义位于libswscale\utils.c，如下所示。

[cpp] view plaincopy

int sws_setColorspaceDetails(struct SwsContext *c, const int inv_table[4],
int srcRange, const int table[4], int dstRange,
int brightness, int contrast, int saturation)
{
const AVPixFmtDescriptor *desc_dst;
const AVPixFmtDescriptor *desc_src;
int need_reinit = 0;
memmove(c->srcColorspaceTable, inv_table, sizeof(int) * 4);
memmove(c->dstColorspaceTable, table, sizeof(int) * 4);
handle_formats(c);
desc_dst = av_pix_fmt_desc_get(c->dstFormat);
desc_src = av_pix_fmt_desc_get(c->srcFormat);
if(!isYUV(c->dstFormat) && !isGray(c->dstFormat))
dstRange = 0;
if(!isYUV(c->srcFormat) && !isGray(c->srcFormat))
srcRange = 0;
c->brightness = brightness;
c->contrast = contrast;
c->saturation = saturation;
if (c->srcRange != srcRange || c->dstRange != dstRange)
need_reinit = 1;
c->srcRange = srcRange;
c->dstRange = dstRange;
//The srcBpc check is possibly wrong but we seem to lack a definitive reference to test this
//and what we have in ticket 2939 looks better with this check
if (need_reinit && (c->srcBpc == 8 || !isYUV(c->srcFormat)))
ff_sws_init_range_convert(c);
if ((isYUV(c->dstFormat) || isGray(c->dstFormat)) && (isYUV(c->srcFormat) || isGray(c->srcFormat)))
return -1;
c->dstFormatBpp = av_get_bits_per_pixel(desc_dst);
c->srcFormatBpp = av_get_bits_per_pixel(desc_src);
if (!isYUV(c->dstFormat) && !isGray(c->dstFormat)) {
ff_yuv2rgb_c_init_tables(c, inv_table, srcRange, brightness,
contrast, saturation);
// FIXME factorize
if (ARCH_PPC)
ff_yuv2rgb_init_tables_ppc(c, inv_table, brightness,
contrast, saturation);
}
fill_rgb2yuv_table(c, table, dstRange);
return 0;
}

从sws_setColorspaceDetails()定义中可以看出，该函数将输入的参数分别赋值给了相应的变量，并且在最后调用了一个函数fill_rgb2yuv_table()。fill_rgb2yuv_table()函数还没有弄懂，暂时不记录。

sws_getCoefficients()

sws_getCoefficients()用于获取描述颜色空间的参数表。它的声明如下。

[cpp] view plaincopy

/**
* Return a pointer to yuv<->rgb coefficients for the given colorspace
* suitable for sws_setColorspaceDetails().
*
* @param colorspace One of the SWS_CS_* macros. If invalid,
* SWS_CS_DEFAULT is used.
*/
const int *sws_getCoefficients(int colorspace);

其中colorspace可以取值如下变量。默认的取值SWS_CS_DEFAULT等同于SWS_CS_ITU601或者SWS_CS_SMPTE170M。

[cpp] view plaincopy

#define SWS_CS_ITU709 1
#define SWS_CS_FCC 4
#define SWS_CS_ITU601 5
#define SWS_CS_ITU624 5
#define SWS_CS_SMPTE170M 5
#define SWS_CS_SMPTE240M 7
#define SWS_CS_DEFAULT 5

下面看一下sws_getCoefficients()的定义，位于libswscale\yuv2rgb.c，如下所示。

[cpp] view plaincopy

const int *sws_getCoefficients(int colorspace)
{
if (colorspace > 7 || colorspace < 0)
colorspace = SWS_CS_DEFAULT;
return ff_yuv2rgb_coeffs[colorspace];
}

可以看出它返回了一个名称为ff_yuv2rgb_coeffs的数组中的一个元素，该数组的定义如下所示。

[cpp] view plaincopy

const int32_t ff_yuv2rgb_coeffs[8][4] = {
{ 117504, 138453, 13954, 34903 }, /* no sequence_display_extension */
{ 117504, 138453, 13954, 34903 }, /* ITU-R Rec. 709 (1990) */
{ 104597, 132201, 25675, 53279 }, /* unspecified */
{ 104597, 132201, 25675, 53279 }, /* reserved */
{ 104448, 132798, 24759, 53109 }, /* FCC */
{ 104597, 132201, 25675, 53279 }, /* ITU-R Rec. 624-4 System B, G */
{ 104597, 132201, 25675, 53279 }, /* SMPTE 170M */
{ 117579, 136230, 16907, 35559 } /* SMPTE 240M (1987) */
};

4.一些输入参数的检测。

例如：如果没有设置图像拉伸方法的话，默认设置为SWS_BICUBIC；如果输入和输出图像的宽高小于等于0的话，也会返回错误信息。有关这方面的代码比较多，简单举个例子。

[cpp] view plaincopy

i = flags & (SWS_POINT |
SWS_AREA |
SWS_BILINEAR |
SWS_FAST_BILINEAR |
SWS_BICUBIC |
SWS_X |
SWS_GAUSS |
SWS_LANCZOS |
SWS_SINC |
SWS_SPLINE |
SWS_BICUBLIN);
/* provide a default scaler if not set by caller */
if (!i) {
if (dstW < srcW && dstH < srcH)
flags |= SWS_BICUBIC;
else if (dstW > srcW && dstH > srcH)
flags |= SWS_BICUBIC;
else
flags |= SWS_BICUBIC;
c->flags = flags;
} else if (i & (i - 1)) {
av_log(c, AV_LOG_ERROR,
"Exactly one scaler algorithm must be chosen, got %X\n", i);
return AVERROR(EINVAL);
}
/* sanity check */
if (srcW < 1 || srcH < 1 || dstW < 1 || dstH < 1) {
/* FIXME check if these are enough and try to lower them after
* fixing the relevant parts of the code */
av_log(c, AV_LOG_ERROR, "%dx%d -> %dx%d is invalid scaling dimension\n",
srcW, srcH, dstW, dstH);
return AVERROR(EINVAL);
}

5.初始化Filter。这一步根据拉伸方法的不同，初始化不同的Filter。

这一部分的工作在函数initFilter()中完成，暂时不详细分析。

6.如果flags中设置了“打印信息”选项SWS_PRINT_INFO，则输出信息。

SwsContext初始化的时候，可以给flags设置SWS_PRINT_INFO标记。这样SwsContext初始化完成的时候就可以打印出一些配置信息。与打印相关的代码如下所示。

[cpp] view plaincopy

if (flags & SWS_PRINT_INFO) {
const char *scaler = NULL, *cpucaps;
for (i = 0; i < FF_ARRAY_ELEMS(scale_algorithms); i++) {
if (flags & scale_algorithms[i].flag) {
scaler = scale_algorithms[i].description;
break;
}
}
if (!scaler)
scaler = "ehh flags invalid?!";
av_log(c, AV_LOG_INFO, "%s scaler, from %s to %s%s ",
scaler,
av_get_pix_fmt_name(srcFormat),
#ifdef DITHER1XBPP
dstFormat == AV_PIX_FMT_BGR555 || dstFormat == AV_PIX_FMT_BGR565 ||
dstFormat == AV_PIX_FMT_RGB444BE || dstFormat == AV_PIX_FMT_RGB444LE ||
dstFormat == AV_PIX_FMT_BGR444BE || dstFormat == AV_PIX_FMT_BGR444LE ?
"dithered " : "",
#else
"",
#endif
av_get_pix_fmt_name(dstFormat));
if (INLINE_MMXEXT(cpu_flags))
cpucaps = "MMXEXT";
else if (INLINE_AMD3DNOW(cpu_flags))
cpucaps = "3DNOW";
else if (INLINE_MMX(cpu_flags))
cpucaps = "MMX";
else if (PPC_ALTIVEC(cpu_flags))
cpucaps = "AltiVec";
else
cpucaps = "C";
av_log(c, AV_LOG_INFO, "using %s\n", cpucaps);
av_log(c, AV_LOG_VERBOSE, "%dx%d -> %dx%d\n", srcW, srcH, dstW, dstH);
av_log(c, AV_LOG_DEBUG,
"lum srcW=%d srcH=%d dstW=%d dstH=%d xInc=%d yInc=%d\n",
c->srcW, c->srcH, c->dstW, c->dstH, c->lumXInc, c->lumYInc);
av_log(c, AV_LOG_DEBUG,
"chr srcW=%d srcH=%d dstW=%d dstH=%d xInc=%d yInc=%d\n",
c->chrSrcW, c->chrSrcH, c->chrDstW, c->chrDstH,
c->chrXInc, c->chrYInc);
}

7.如果不需要拉伸的话，就会调用ff_get_unscaled_swscale()将特定的像素转换函数的指针赋值给SwsContext中的swscale指针。

ff_get_unscaled_swscale()

ff_get_unscaled_swscale()的定义如下所示。该函数根据输入图像像素格式和输出图像像素格式，选择不同的像素格式转换函数。

[cpp] view plaincopy

void ff_get_unscaled_swscale(SwsContext *c)
{
const enum AVPixelFormat srcFormat = c->srcFormat;
const enum AVPixelFormat dstFormat = c->dstFormat;
const int flags = c->flags;
const int dstH = c->dstH;
int needsDither;
needsDither = isAnyRGB(dstFormat) &&
c->dstFormatBpp < 24 &&
(c->dstFormatBpp < c->srcFormatBpp || (!isAnyRGB(srcFormat)));
/* yv12_to_nv12 */
if ((srcFormat == AV_PIX_FMT_YUV420P || srcFormat == AV_PIX_FMT_YUVA420P) &&
(dstFormat == AV_PIX_FMT_NV12 || dstFormat == AV_PIX_FMT_NV21)) {
c->swscale = planarToNv12Wrapper;
}
/* nv12_to_yv12 */
if (dstFormat == AV_PIX_FMT_YUV420P &&
(srcFormat == AV_PIX_FMT_NV12 || srcFormat == AV_PIX_FMT_NV21)) {
c->swscale = nv12ToPlanarWrapper;
}
/* yuv2bgr */
if ((srcFormat == AV_PIX_FMT_YUV420P || srcFormat == AV_PIX_FMT_YUV422P ||
srcFormat == AV_PIX_FMT_YUVA420P) && isAnyRGB(dstFormat) &&
!(flags & SWS_ACCURATE_RND) && (c->dither == SWS_DITHER_BAYER || c->dither == SWS_DITHER_AUTO) && !(dstH & 1)) {
c->swscale = ff_yuv2rgb_get_func_ptr(c);
}
if (srcFormat == AV_PIX_FMT_YUV410P && !(dstH & 3) &&
(dstFormat == AV_PIX_FMT_YUV420P || dstFormat == AV_PIX_FMT_YUVA420P) &&
!(flags & SWS_BITEXACT)) {
c->swscale = yvu9ToYv12Wrapper;
}
/* bgr24toYV12 */
if (srcFormat == AV_PIX_FMT_BGR24 &&
(dstFormat == AV_PIX_FMT_YUV420P || dstFormat == AV_PIX_FMT_YUVA420P) &&
!(flags & SWS_ACCURATE_RND))
c->swscale = bgr24ToYv12Wrapper;
/* RGB/BGR -> RGB/BGR (no dither needed forms) */
if (isAnyRGB(srcFormat) && isAnyRGB(dstFormat) && findRgbConvFn(c)
&& (!needsDither || (c->flags&(SWS_FAST_BILINEAR|SWS_POINT))))
c->swscale = rgbToRgbWrapper;
if ((srcFormat == AV_PIX_FMT_GBRP && dstFormat == AV_PIX_FMT_GBRAP) ||
(srcFormat == AV_PIX_FMT_GBRAP && dstFormat == AV_PIX_FMT_GBRP))
c->swscale = planarRgbToplanarRgbWrapper;
#define isByteRGB(f) ( \
f == AV_PIX_FMT_RGB32 || \
f == AV_PIX_FMT_RGB32_1 || \
f == AV_PIX_FMT_RGB24 || \
f == AV_PIX_FMT_BGR32 || \
f == AV_PIX_FMT_BGR32_1 || \
f == AV_PIX_FMT_BGR24)
if (srcFormat == AV_PIX_FMT_GBRP && isPlanar(srcFormat) && isByteRGB(dstFormat))
c->swscale = planarRgbToRgbWrapper;
if ((srcFormat == AV_PIX_FMT_RGB48LE || srcFormat == AV_PIX_FMT_RGB48BE ||
srcFormat == AV_PIX_FMT_BGR48LE || srcFormat == AV_PIX_FMT_BGR48BE ||
srcFormat == AV_PIX_FMT_RGBA64LE || srcFormat == AV_PIX_FMT_RGBA64BE ||
srcFormat == AV_PIX_FMT_BGRA64LE || srcFormat == AV_PIX_FMT_BGRA64BE) &&
(dstFormat == AV_PIX_FMT_GBRP9LE || dstFormat == AV_PIX_FMT_GBRP9BE ||
dstFormat == AV_PIX_FMT_GBRP10LE || dstFormat == AV_PIX_FMT_GBRP10BE ||
dstFormat == AV_PIX_FMT_GBRP12LE || dstFormat == AV_PIX_FMT_GBRP12BE ||
dstFormat == AV_PIX_FMT_GBRP14LE || dstFormat == AV_PIX_FMT_GBRP14BE ||
dstFormat == AV_PIX_FMT_GBRP16LE || dstFormat == AV_PIX_FMT_GBRP16BE ||
dstFormat == AV_PIX_FMT_GBRAP16LE || dstFormat == AV_PIX_FMT_GBRAP16BE ))
c->swscale = Rgb16ToPlanarRgb16Wrapper;
if ((srcFormat == AV_PIX_FMT_GBRP9LE || srcFormat == AV_PIX_FMT_GBRP9BE ||
srcFormat == AV_PIX_FMT_GBRP16LE || srcFormat == AV_PIX_FMT_GBRP16BE ||
srcFormat == AV_PIX_FMT_GBRP10LE || srcFormat == AV_PIX_FMT_GBRP10BE ||
srcFormat == AV_PIX_FMT_GBRP12LE || srcFormat == AV_PIX_FMT_GBRP12BE ||
srcFormat == AV_PIX_FMT_GBRP14LE || srcFormat == AV_PIX_FMT_GBRP14BE ||
srcFormat == AV_PIX_FMT_GBRAP16LE || srcFormat == AV_PIX_FMT_GBRAP16BE) &&
(dstFormat == AV_PIX_FMT_RGB48LE || dstFormat == AV_PIX_FMT_RGB48BE ||
dstFormat == AV_PIX_FMT_BGR48LE || dstFormat == AV_PIX_FMT_BGR48BE ||
dstFormat == AV_PIX_FMT_RGBA64LE || dstFormat == AV_PIX_FMT_RGBA64BE ||
dstFormat == AV_PIX_FMT_BGRA64LE || dstFormat == AV_PIX_FMT_BGRA64BE))
c->swscale = planarRgb16ToRgb16Wrapper;
if (av_pix_fmt_desc_get(srcFormat)->comp[0].depth_minus1 == 7 &&
isPackedRGB(srcFormat) && dstFormat == AV_PIX_FMT_GBRP)
c->swscale = rgbToPlanarRgbWrapper;
if (isBayer(srcFormat)) {
if (dstFormat == AV_PIX_FMT_RGB24)
c->swscale = bayer_to_rgb24_wrapper;
else if (dstFormat == AV_PIX_FMT_YUV420P)
c->swscale = bayer_to_yv12_wrapper;
else if (!isBayer(dstFormat)) {
av_log(c, AV_LOG_ERROR, "unsupported bayer conversion\n");
av_assert0(0);
}
}
/* bswap 16 bits per pixel/component packed formats */
if (IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_BGGR16) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_RGGB16) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_GBRG16) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_GRBG16) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR444) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR48) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGRA64) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR555) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR565) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGRA64) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GRAY16) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YA16) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP9) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP10) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP12) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP14) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP16) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRAP16) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB444) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB48) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGBA64) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB555) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB565) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGBA64) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_XYZ12) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P9) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P10) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P12) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P14) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P16) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P9) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P10) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P12) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P14) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P16) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P9) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P10) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P12) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P14) ||
IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P16))
c->swscale = packed_16bpc_bswap;
if (usePal(srcFormat) && isByteRGB(dstFormat))
c->swscale = palToRgbWrapper;
if (srcFormat == AV_PIX_FMT_YUV422P) {
if (dstFormat == AV_PIX_FMT_YUYV422)
c->swscale = yuv422pToYuy2Wrapper;
else if (dstFormat == AV_PIX_FMT_UYVY422)
c->swscale = yuv422pToUyvyWrapper;
}
/* LQ converters if -sws 0 or -sws 4*/
if (c->flags&(SWS_FAST_BILINEAR|SWS_POINT)) {
/* yv12_to_yuy2 */
if (srcFormat == AV_PIX_FMT_YUV420P || srcFormat == AV_PIX_FMT_YUVA420P) {
if (dstFormat == AV_PIX_FMT_YUYV422)
c->swscale = planarToYuy2Wrapper;
else if (dstFormat == AV_PIX_FMT_UYVY422)
c->swscale = planarToUyvyWrapper;
}
}
if (srcFormat == AV_PIX_FMT_YUYV422 &&
(dstFormat == AV_PIX_FMT_YUV420P || dstFormat == AV_PIX_FMT_YUVA420P))
c->swscale = yuyvToYuv420Wrapper;
if (srcFormat == AV_PIX_FMT_UYVY422 &&
(dstFormat == AV_PIX_FMT_YUV420P || dstFormat == AV_PIX_FMT_YUVA420P))
c->swscale = uyvyToYuv420Wrapper;
if (srcFormat == AV_PIX_FMT_YUYV422 && dstFormat == AV_PIX_FMT_YUV422P)
c->swscale = yuyvToYuv422Wrapper;
if (srcFormat == AV_PIX_FMT_UYVY422 && dstFormat == AV_PIX_FMT_YUV422P)
c->swscale = uyvyToYuv422Wrapper;
#define isPlanarGray(x) (isGray(x) && (x) != AV_PIX_FMT_YA8 && (x) != AV_PIX_FMT_YA16LE && (x) != AV_PIX_FMT_YA16BE)
/* simple copy */
if ( srcFormat == dstFormat ||
(srcFormat == AV_PIX_FMT_YUVA420P && dstFormat == AV_PIX_FMT_YUV420P) ||
(srcFormat == AV_PIX_FMT_YUV420P && dstFormat == AV_PIX_FMT_YUVA420P) ||
(isPlanarYUV(srcFormat) && isPlanarGray(dstFormat)) ||
(isPlanarYUV(dstFormat) && isPlanarGray(srcFormat)) ||
(isPlanarGray(dstFormat) && isPlanarGray(srcFormat)) ||
(isPlanarYUV(srcFormat) && isPlanarYUV(dstFormat) &&
c->chrDstHSubSample == c->chrSrcHSubSample &&
c->chrDstVSubSample == c->chrSrcVSubSample &&
dstFormat != AV_PIX_FMT_NV12 && dstFormat != AV_PIX_FMT_NV21 &&
srcFormat != AV_PIX_FMT_NV12 && srcFormat != AV_PIX_FMT_NV21))
{
if (isPacked(c->srcFormat))
c->swscale = packedCopyWrapper;
else /* Planar YUV or gray */
c->swscale = planarCopyWrapper;
}
if (ARCH_PPC)
ff_get_unscaled_swscale_ppc(c);
// if (ARCH_ARM)
// ff_get_unscaled_swscale_arm(c);
}

从ff_get_unscaled_swscale()源代码中可以看出，赋值给SwsContext的swscale指针的函数名称大多数为XXXWrapper()。实际上这些函数封装了一些基本的像素格式转换函数。例如yuyvToYuv422Wrapper()的定义如下所示。

[cpp] view plaincopy

static int yuyvToYuv422Wrapper(SwsContext *c, const uint8_t *src[],
int srcStride[], int srcSliceY, int srcSliceH,
uint8_t *dstParam[], int dstStride[])
{
uint8_t *ydst = dstParam[0] + dstStride[0] * srcSliceY;
uint8_t *udst = dstParam[1] + dstStride[1] * srcSliceY;
uint8_t *vdst = dstParam[2] + dstStride[2] * srcSliceY;
yuyvtoyuv422(ydst, udst, vdst, src[0], c->srcW, srcSliceH, dstStride[0],
dstStride[1], srcStride[0]);
return srcSliceH;
}

从yuyvToYuv422Wrapper()的定义中可以看出，它调用了yuyvtoyuv422()。而yuyvtoyuv422()则是rgb2rgb.c中的一个函数，用于将YUVU转换为YUV422（该函数在前文中已经记录）。

8.如果需要拉伸的话，就会调用ff_getSwsFunc()将通用的swscale()赋值给SwsContext中的swscale指针，然后返回。
上一步骤（图像不用缩放）实际上是一种不太常见的情况，更多的情况下会执行本步骤。这个时候就会调用ff_getSwsFunc()获取图像的缩放函数。

ff_getSwsFunc()

ff_getSwsFunc()用于获取通用的swscale()函数。该函数的定义如下。

[cpp] view plaincopy

SwsFunc ff_getSwsFunc(SwsContext *c)
{
sws_init_swscale(c);
if (ARCH_PPC)
ff_sws_init_swscale_ppc(c);
if (ARCH_X86)
ff_sws_init_swscale_x86(c);
return swscale;
}

从源代码中可以看出ff_getSwsFunc()调用了函数sws_init_swscale()。如果系统支持X86汇编的话，还会调用ff_sws_init_swscale_x86()。

sws_init_swscale()

sws_init_swscale()的定义位于libswscale\swscale.c，如下所示。

[cpp] view plaincopy

static av_cold void sws_init_swscale(SwsContext *c)
{
enum AVPixelFormat srcFormat = c->srcFormat;
ff_sws_init_output_funcs(c, &c->yuv2plane1, &c->yuv2planeX,
&c->yuv2nv12cX, &c->yuv2packed1,
&c->yuv2packed2, &c->yuv2packedX, &c->yuv2anyX);
ff_sws_init_input_funcs(c);
if (c->srcBpc == 8) {
if (c->dstBpc <= 14) {
c->hyScale = c->hcScale = hScale8To15_c;
if (c->flags & SWS_FAST_BILINEAR) {
c->hyscale_fast = ff_hyscale_fast_c;
c->hcscale_fast = ff_hcscale_fast_c;
}
} else {
c->hyScale = c->hcScale = hScale8To19_c;
}
} else {
c->hyScale = c->hcScale = c->dstBpc > 14 ? hScale16To19_c
: hScale16To15_c;
}
ff_sws_init_range_convert(c);
if (!(isGray(srcFormat) || isGray(c->dstFormat) ||
srcFormat == AV_PIX_FMT_MONOBLACK || srcFormat == AV_PIX_FMT_MONOWHITE))
c->needs_hcscale = 1;
}

从函数中可以看出，sws_init_swscale()主要调用了3个函数：ff_sws_init_output_funcs()，ff_sws_init_input_funcs()，ff_sws_init_range_convert()。其中，ff_sws_init_output_funcs()用于初始化输出的函数，ff_sws_init_input_funcs()用于初始化输入的函数，ff_sws_init_range_convert()用于初始化像素值范围转换的函数。

ff_sws_init_output_funcs()

ff_sws_init_output_funcs()用于初始化“输出函数”。“输出函数”在libswscale中的作用就是将处理后的一行像素数据输出出来。ff_sws_init_output_funcs()的定义位于libswscale\output.c，如下所示。

[cpp] view plaincopy

av_cold void ff_sws_init_output_funcs(SwsContext *c,
yuv2planar1_fn *yuv2plane1,
yuv2planarX_fn *yuv2planeX,
yuv2interleavedX_fn *yuv2nv12cX,
yuv2packed1_fn *yuv2packed1,
yuv2packed2_fn *yuv2packed2,
yuv2packedX_fn *yuv2packedX,
yuv2anyX_fn *yuv2anyX)
{
enum AVPixelFormat dstFormat = c->dstFormat;
const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(dstFormat);
if (is16BPS(dstFormat)) {
*yuv2planeX = isBE(dstFormat) ? yuv2planeX_16BE_c : yuv2planeX_16LE_c;
*yuv2plane1 = isBE(dstFormat) ? yuv2plane1_16BE_c : yuv2plane1_16LE_c;
} else if (is9_OR_10BPS(dstFormat)) {
if (desc->comp[0].depth_minus1 == 8) {
*yuv2planeX = isBE(dstFormat) ? yuv2planeX_9BE_c : yuv2planeX_9LE_c;
*yuv2plane1 = isBE(dstFormat) ? yuv2plane1_9BE_c : yuv2plane1_9LE_c;
} else if (desc->comp[0].depth_minus1 == 9) {
*yuv2planeX = isBE(dstFormat) ? yuv2planeX_10BE_c : yuv2planeX_10LE_c;
*yuv2plane1 = isBE(dstFormat) ? yuv2plane1_10BE_c : yuv2plane1_10LE_c;
} else if (desc->comp[0].depth_minus1 == 11) {
*yuv2planeX = isBE(dstFormat) ? yuv2planeX_12BE_c : yuv2planeX_12LE_c;
*yuv2plane1 = isBE(dstFormat) ? yuv2plane1_12BE_c : yuv2plane1_12LE_c;
} else if (desc->comp[0].depth_minus1 == 13) {
*yuv2planeX = isBE(dstFormat) ? yuv2planeX_14BE_c : yuv2planeX_14LE_c;
*yuv2plane1 = isBE(dstFormat) ? yuv2plane1_14BE_c : yuv2plane1_14LE_c;
} else
av_assert0(0);
} else {
*yuv2plane1 = yuv2plane1_8_c;
*yuv2planeX = yuv2planeX_8_c;
if (dstFormat == AV_PIX_FMT_NV12 || dstFormat == AV_PIX_FMT_NV21)
*yuv2nv12cX = yuv2nv12cX_c;
}
if(c->flags & SWS_FULL_CHR_H_INT) {
switch (dstFormat) {
case AV_PIX_FMT_RGBA:
#if CONFIG_SMALL
*yuv2packedX = yuv2rgba32_full_X_c;
*yuv2packed2 = yuv2rgba32_full_2_c;
*yuv2packed1 = yuv2rgba32_full_1_c;
#else
#if CONFIG_SWSCALE_ALPHA
if (c->alpPixBuf) {
*yuv2packedX = yuv2rgba32_full_X_c;
*yuv2packed2 = yuv2rgba32_full_2_c;
*yuv2packed1 = yuv2rgba32_full_1_c;
} else
#endif /* CONFIG_SWSCALE_ALPHA */
{
*yuv2packedX = yuv2rgbx32_full_X_c;
*yuv2packed2 = yuv2rgbx32_full_2_c;
*yuv2packed1 = yuv2rgbx32_full_1_c;
}
#endif /* !CONFIG_SMALL */
break;
case AV_PIX_FMT_ARGB:
#if CONFIG_SMALL
*yuv2packedX = yuv2argb32_full_X_c;
*yuv2packed2 = yuv2argb32_full_2_c;
*yuv2packed1 = yuv2argb32_full_1_c;
#else
#if CONFIG_SWSCALE_ALPHA
if (c->alpPixBuf) {
*yuv2packedX = yuv2argb32_full_X_c;
*yuv2packed2 = yuv2argb32_full_2_c;
*yuv2packed1 = yuv2argb32_full_1_c;
} else
#endif /* CONFIG_SWSCALE_ALPHA */
{
*yuv2packedX = yuv2xrgb32_full_X_c;
*yuv2packed2 = yuv2xrgb32_full_2_c;
*yuv2packed1 = yuv2xrgb32_full_1_c;
}
#endif /* !CONFIG_SMALL */
break;
case AV_PIX_FMT_BGRA:
#if CONFIG_SMALL
*yuv2packedX = yuv2bgra32_full_X_c;
*yuv2packed2 = yuv2bgra32_full_2_c;
*yuv2packed1 = yuv2bgra32_full_1_c;
#else
#if CONFIG_SWSCALE_ALPHA
if (c->alpPixBuf) {
*yuv2packedX = yuv2bgra32_full_X_c;
*yuv2packed2 = yuv2bgra32_full_2_c;
*yuv2packed1 = yuv2bgra32_full_1_c;
} else
#endif /* CONFIG_SWSCALE_ALPHA */
{
*yuv2packedX = yuv2bgrx32_full_X_c;
*yuv2packed2 = yuv2bgrx32_full_2_c;
*yuv2packed1 = yuv2bgrx32_full_1_c;
}
#endif /* !CONFIG_SMALL */
break;
case AV_PIX_FMT_ABGR:
#if CONFIG_SMALL
*yuv2packedX = yuv2abgr32_full_X_c;
*yuv2packed2 = yuv2abgr32_full_2_c;
*yuv2packed1 = yuv2abgr32_full_1_c;
#else
#if CONFIG_SWSCALE_ALPHA
if (c->alpPixBuf) {
*yuv2packedX = yuv2abgr32_full_X_c;
*yuv2packed2 = yuv2abgr32_full_2_c;
*yuv2packed1 = yuv2abgr32_full_1_c;
} else
#endif /* CONFIG_SWSCALE_ALPHA */
{
*yuv2packedX = yuv2xbgr32_full_X_c;
*yuv2packed2 = yuv2xbgr32_full_2_c;
*yuv2packed1 = yuv2xbgr32_full_1_c;
}
#endif /* !CONFIG_SMALL */
break;
case AV_PIX_FMT_RGB24:
*yuv2packedX = yuv2rgb24_full_X_c;
*yuv2packed2 = yuv2rgb24_full_2_c;
*yuv2packed1 = yuv2rgb24_full_1_c;
break;
case AV_PIX_FMT_BGR24:
*yuv2packedX = yuv2bgr24_full_X_c;
*yuv2packed2 = yuv2bgr24_full_2_c;
*yuv2packed1 = yuv2bgr24_full_1_c;
break;
case AV_PIX_FMT_BGR4_BYTE:
*yuv2packedX = yuv2bgr4_byte_full_X_c;
*yuv2packed2 = yuv2bgr4_byte_full_2_c;
*yuv2packed1 = yuv2bgr4_byte_full_1_c;
break;
case AV_PIX_FMT_RGB4_BYTE:
*yuv2packedX = yuv2rgb4_byte_full_X_c;
*yuv2packed2 = yuv2rgb4_byte_full_2_c;
*yuv2packed1 = yuv2rgb4_byte_full_1_c;
break;
case AV_PIX_FMT_BGR8:
*yuv2packedX = yuv2bgr8_full_X_c;
*yuv2packed2 = yuv2bgr8_full_2_c;
*yuv2packed1 = yuv2bgr8_full_1_c;
break;
case AV_PIX_FMT_RGB8:
*yuv2packedX = yuv2rgb8_full_X_c;
*yuv2packed2 = yuv2rgb8_full_2_c;
*yuv2packed1 = yuv2rgb8_full_1_c;
break;
case AV_PIX_FMT_GBRP:
case AV_PIX_FMT_GBRP9BE:
case AV_PIX_FMT_GBRP9LE:
case AV_PIX_FMT_GBRP10BE:
case AV_PIX_FMT_GBRP10LE:
case AV_PIX_FMT_GBRP12BE:
case AV_PIX_FMT_GBRP12LE:
case AV_PIX_FMT_GBRP14BE:
case AV_PIX_FMT_GBRP14LE:
case AV_PIX_FMT_GBRP16BE:
case AV_PIX_FMT_GBRP16LE:
case AV_PIX_FMT_GBRAP:
*yuv2anyX = yuv2gbrp_full_X_c;
break;
}
if (!*yuv2packedX && !*yuv2anyX)
goto YUV_PACKED;
} else {
YUV_PACKED:
switch (dstFormat) {
case AV_PIX_FMT_RGBA64LE:
#if CONFIG_SWSCALE_ALPHA
if (c->alpPixBuf) {
*yuv2packed1 = yuv2rgba64le_1_c;
*yuv2packed2 = yuv2rgba64le_2_c;
*yuv2packedX = yuv2rgba64le_X_c;
} else
#endif /* CONFIG_SWSCALE_ALPHA */
{
*yuv2packed1 = yuv2rgbx64le_1_c;
*yuv2packed2 = yuv2rgbx64le_2_c;
*yuv2packedX = yuv2rgbx64le_X_c;
}
break;
case AV_PIX_FMT_RGBA64BE:
#if CONFIG_SWSCALE_ALPHA
if (c->alpPixBuf) {
*yuv2packed1 = yuv2rgba64be_1_c;
*yuv2packed2 = yuv2rgba64be_2_c;
*yuv2packedX = yuv2rgba64be_X_c;
} else
#endif /* CONFIG_SWSCALE_ALPHA */
{
*yuv2packed1 = yuv2rgbx64be_1_c;
*yuv2packed2 = yuv2rgbx64be_2_c;
*yuv2packedX = yuv2rgbx64be_X_c;
}
break;
case AV_PIX_FMT_BGRA64LE:
#if CONFIG_SWSCALE_ALPHA
if (c->alpPixBuf) {
*yuv2packed1 = yuv2bgra64le_1_c;
*yuv2packed2 = yuv2bgra64le_2_c;
*yuv2packedX = yuv2bgra64le_X_c;
} else
#endif /* CONFIG_SWSCALE_ALPHA */
{
*yuv2packed1 = yuv2bgrx64le_1_c;
*yuv2packed2 = yuv2bgrx64le_2_c;
*yuv2packedX = yuv2bgrx64le_X_c;
}
break;
case AV_PIX_FMT_BGRA64BE:
#if CONFIG_SWSCALE_ALPHA
if (c->alpPixBuf) {
*yuv2packed1 = yuv2bgra64be_1_c;
*yuv2packed2 = yuv2bgra64be_2_c;
*yuv2packedX = yuv2bgra64be_X_c;
} else
#endif /* CONFIG_SWSCALE_ALPHA */
{
*yuv2packed1 = yuv2bgrx64be_1_c;
*yuv2packed2 = yuv2bgrx64be_2_c;
*yuv2packedX = yuv2bgrx64be_X_c;
}
break;
case AV_PIX_FMT_RGB48LE:
*yuv2packed1 = yuv2rgb48le_1_c;
*yuv2packed2 = yuv2rgb48le_2_c;
*yuv2packedX = yuv2rgb48le_X_c;
break;
case AV_PIX_FMT_RGB48BE:
*yuv2packed1 = yuv2rgb48be_1_c;
*yuv2packed2 = yuv2rgb48be_2_c;
*yuv2packedX = yuv2rgb48be_X_c;
break;
case AV_PIX_FMT_BGR48LE:
*yuv2packed1 = yuv2bgr48le_1_c;
*yuv2packed2 = yuv2bgr48le_2_c;
*yuv2packedX = yuv2bgr48le_X_c;
break;
case AV_PIX_FMT_BGR48BE:
*yuv2packed1 = yuv2bgr48be_1_c;
*yuv2packed2 = yuv2bgr48be_2_c;
*yuv2packedX = yuv2bgr48be_X_c;
break;
case AV_PIX_FMT_RGB32:
case AV_PIX_FMT_BGR32:
#if CONFIG_SMALL
*yuv2packed1 = yuv2rgb32_1_c;
*yuv2packed2 = yuv2rgb32_2_c;
*yuv2packedX = yuv2rgb32_X_c;
#else
#if CONFIG_SWSCALE_ALPHA
if (c->alpPixBuf) {
*yuv2packed1 = yuv2rgba32_1_c;
*yuv2packed2 = yuv2rgba32_2_c;
*yuv2packedX = yuv2rgba32_X_c;
} else
#endif /* CONFIG_SWSCALE_ALPHA */
{
*yuv2packed1 = yuv2rgbx32_1_c;
*yuv2packed2 = yuv2rgbx32_2_c;
*yuv2packedX = yuv2rgbx32_X_c;
}
#endif /* !CONFIG_SMALL */
break;
case AV_PIX_FMT_RGB32_1:
case AV_PIX_FMT_BGR32_1:
#if CONFIG_SMALL
*yuv2packed1 = yuv2rgb32_1_1_c;
*yuv2packed2 = yuv2rgb32_1_2_c;
*yuv2packedX = yuv2rgb32_1_X_c;
#else
#if CONFIG_SWSCALE_ALPHA
if (c->alpPixBuf) {
*yuv2packed1 = yuv2rgba32_1_1_c;
*yuv2packed2 = yuv2rgba32_1_2_c;
*yuv2packedX = yuv2rgba32_1_X_c;
} else
#endif /* CONFIG_SWSCALE_ALPHA */
{
*yuv2packed1 = yuv2rgbx32_1_1_c;
*yuv2packed2 = yuv2rgbx32_1_2_c;
*yuv2packedX = yuv2rgbx32_1_X_c;
}
#endif /* !CONFIG_SMALL */
break;
case AV_PIX_FMT_RGB24:
*yuv2packed1 = yuv2rgb24_1_c;
*yuv2packed2 = yuv2rgb24_2_c;
*yuv2packedX = yuv2rgb24_X_c;
break;
case AV_PIX_FMT_BGR24:
*yuv2packed1 = yuv2bgr24_1_c;
*yuv2packed2 = yuv2bgr24_2_c;
*yuv2packedX = yuv2bgr24_X_c;
break;
case AV_PIX_FMT_RGB565LE:
case AV_PIX_FMT_RGB565BE:
case AV_PIX_FMT_BGR565LE:
case AV_PIX_FMT_BGR565BE:
*yuv2packed1 = yuv2rgb16_1_c;
*yuv2packed2 = yuv2rgb16_2_c;
*yuv2packedX = yuv2rgb16_X_c;
break;
case AV_PIX_FMT_RGB555LE:
case AV_PIX_FMT_RGB555BE:
case AV_PIX_FMT_BGR555LE:
case AV_PIX_FMT_BGR555BE:
*yuv2packed1 = yuv2rgb15_1_c;
*yuv2packed2 = yuv2rgb15_2_c;
*yuv2packedX = yuv2rgb15_X_c;
break;
case AV_PIX_FMT_RGB444LE:
case AV_PIX_FMT_RGB444BE:
case AV_PIX_FMT_BGR444LE:
case AV_PIX_FMT_BGR444BE:
*yuv2packed1 = yuv2rgb12_1_c;
*yuv2packed2 = yuv2rgb12_2_c;
*yuv2packedX = yuv2rgb12_X_c;
break;
case AV_PIX_FMT_RGB8:
case AV_PIX_FMT_BGR8:
*yuv2packed1 = yuv2rgb8_1_c;
*yuv2packed2 = yuv2rgb8_2_c;
*yuv2packedX = yuv2rgb8_X_c;
break;
case AV_PIX_FMT_RGB4:
case AV_PIX_FMT_BGR4:
*yuv2packed1 = yuv2rgb4_1_c;
*yuv2packed2 = yuv2rgb4_2_c;
*yuv2packedX = yuv2rgb4_X_c;
break;
case AV_PIX_FMT_RGB4_BYTE:
case AV_PIX_FMT_BGR4_BYTE:
*yuv2packed1 = yuv2rgb4b_1_c;
*yuv2packed2 = yuv2rgb4b_2_c;
*yuv2packedX = yuv2rgb4b_X_c;
break;
}
}
switch (dstFormat) {
case AV_PIX_FMT_MONOWHITE:
*yuv2packed1 = yuv2monowhite_1_c;
*yuv2packed2 = yuv2monowhite_2_c;
*yuv2packedX = yuv2monowhite_X_c;
break;
case AV_PIX_FMT_MONOBLACK:
*yuv2packed1 = yuv2monoblack_1_c;
*yuv2packed2 = yuv2monoblack_2_c;
*yuv2packedX = yuv2monoblack_X_c;
break;
case AV_PIX_FMT_YUYV422:
*yuv2packed1 = yuv2yuyv422_1_c;
*yuv2packed2 = yuv2yuyv422_2_c;
*yuv2packedX = yuv2yuyv422_X_c;
break;
case AV_PIX_FMT_YVYU422:
*yuv2packed1 = yuv2yvyu422_1_c;
*yuv2packed2 = yuv2yvyu422_2_c;
*yuv2packedX = yuv2yvyu422_X_c;
break;
case AV_PIX_FMT_UYVY422:
*yuv2packed1 = yuv2uyvy422_1_c;
*yuv2packed2 = yuv2uyvy422_2_c;
*yuv2packedX = yuv2uyvy422_X_c;
break;
}
}

ff_sws_init_output_funcs()根据输出像素格式的不同，对以下几个函数指针进行赋值：

yuv2plane1：是yuv2planar1_fn类型的函数指针。该函数用于输出一行水平拉伸后的planar格式数据。数据没有使用垂直拉伸。
yuv2planeX：是yuv2planarX_fn类型的函数指针。该函数用于输出一行水平拉伸后的planar格式数据。数据使用垂直拉伸。
yuv2packed1：是yuv2packed1_fn类型的函数指针。该函数用于输出一行水平拉伸后的packed格式数据。数据没有使用垂直拉伸。
yuv2packed2：是yuv2packed2_fn类型的函数指针。该函数用于输出一行水平拉伸后的packed格式数据。数据使用两行数据进行垂直拉伸。
yuv2packedX：是yuv2packedX_fn类型的函数指针。该函数用于输出一行水平拉伸后的packed格式数据。数据使用垂直拉伸。
yuv2nv12cX：是yuv2interleavedX_fn类型的函数指针。还没有研究该函数。
yuv2anyX：是yuv2anyX_fn类型的函数指针。还没有研究该函数。

ff_sws_init_input_funcs()

ff_sws_init_input_funcs()用于初始化“输入函数”。“输入函数”在libswscale中的作用就是任意格式的像素转换为YUV格式以供后续的处理。ff_sws_init_input_funcs()的定义位于libswscale\input.c，如下所示。

[cpp] view plaincopy

av_cold void ff_sws_init_input_funcs(SwsContext *c)
{
enum AVPixelFormat srcFormat = c->srcFormat;
c->chrToYV12 = NULL;
switch (srcFormat) {
case AV_PIX_FMT_YUYV422:
c->chrToYV12 = yuy2ToUV_c;
break;
case AV_PIX_FMT_YVYU422:
c->chrToYV12 = yvy2ToUV_c;
break;
case AV_PIX_FMT_UYVY422:
c->chrToYV12 = uyvyToUV_c;
break;
case AV_PIX_FMT_NV12:
c->chrToYV12 = nv12ToUV_c;
break;
case AV_PIX_FMT_NV21:
c->chrToYV12 = nv21ToUV_c;
break;
case AV_PIX_FMT_RGB8:
case AV_PIX_FMT_BGR8:
case AV_PIX_FMT_PAL8:
case AV_PIX_FMT_BGR4_BYTE:
case AV_PIX_FMT_RGB4_BYTE:
c->chrToYV12 = palToUV_c;
break;
case AV_PIX_FMT_GBRP9LE:
c->readChrPlanar = planar_rgb9le_to_uv;
break;
case AV_PIX_FMT_GBRP10LE:
c->readChrPlanar = planar_rgb10le_to_uv;
break;
case AV_PIX_FMT_GBRP12LE:
c->readChrPlanar = planar_rgb12le_to_uv;
break;
case AV_PIX_FMT_GBRP14LE:
c->readChrPlanar = planar_rgb14le_to_uv;
break;
case AV_PIX_FMT_GBRAP16LE:
case AV_PIX_FMT_GBRP16LE:
c->readChrPlanar = planar_rgb16le_to_uv;
break;
case AV_PIX_FMT_GBRP9BE:
c->readChrPlanar = planar_rgb9be_to_uv;
break;
case AV_PIX_FMT_GBRP10BE:
c->readChrPlanar = planar_rgb10be_to_uv;
break;
case AV_PIX_FMT_GBRP12BE:
c->readChrPlanar = planar_rgb12be_to_uv;
break;
case AV_PIX_FMT_GBRP14BE:
c->readChrPlanar = planar_rgb14be_to_uv;
break;
case AV_PIX_FMT_GBRAP16BE:
case AV_PIX_FMT_GBRP16BE:
c->readChrPlanar = planar_rgb16be_to_uv;
break;
case AV_PIX_FMT_GBRAP:
case AV_PIX_FMT_GBRP:
c->readChrPlanar = planar_rgb_to_uv;
break;
#if HAVE_BIGENDIAN
case AV_PIX_FMT_YUV444P9LE:
case AV_PIX_FMT_YUV422P9LE:
case AV_PIX_FMT_YUV420P9LE:
case AV_PIX_FMT_YUV422P10LE:
case AV_PIX_FMT_YUV444P10LE:
case AV_PIX_FMT_YUV420P10LE:
case AV_PIX_FMT_YUV422P12LE:
case AV_PIX_FMT_YUV444P12LE:
case AV_PIX_FMT_YUV420P12LE:
case AV_PIX_FMT_YUV422P14LE:
case AV_PIX_FMT_YUV444P14LE:
case AV_PIX_FMT_YUV420P14LE:
case AV_PIX_FMT_YUV420P16LE:
case AV_PIX_FMT_YUV422P16LE:
case AV_PIX_FMT_YUV444P16LE:
case AV_PIX_FMT_YUVA444P9LE:
case AV_PIX_FMT_YUVA422P9LE:
case AV_PIX_FMT_YUVA420P9LE:
case AV_PIX_FMT_YUVA444P10LE:
case AV_PIX_FMT_YUVA422P10LE:
case AV_PIX_FMT_YUVA420P10LE:
case AV_PIX_FMT_YUVA420P16LE:
case AV_PIX_FMT_YUVA422P16LE:
case AV_PIX_FMT_YUVA444P16LE:
c->chrToYV12 = bswap16UV_c;
break;
#else
case AV_PIX_FMT_YUV444P9BE:
case AV_PIX_FMT_YUV422P9BE:
case AV_PIX_FMT_YUV420P9BE:
case AV_PIX_FMT_YUV444P10BE:
case AV_PIX_FMT_YUV422P10BE:
case AV_PIX_FMT_YUV420P10BE:
case AV_PIX_FMT_YUV444P12BE:
case AV_PIX_FMT_YUV422P12BE:
case AV_PIX_FMT_YUV420P12BE:
case AV_PIX_FMT_YUV444P14BE:
case AV_PIX_FMT_YUV422P14BE:
case AV_PIX_FMT_YUV420P14BE:
case AV_PIX_FMT_YUV420P16BE:
case AV_PIX_FMT_YUV422P16BE:
case AV_PIX_FMT_YUV444P16BE:
case AV_PIX_FMT_YUVA444P9BE:
case AV_PIX_FMT_YUVA422P9BE:
case AV_PIX_FMT_YUVA420P9BE:
case AV_PIX_FMT_YUVA444P10BE:
case AV_PIX_FMT_YUVA422P10BE:
case AV_PIX_FMT_YUVA420P10BE:
case AV_PIX_FMT_YUVA420P16BE:
case AV_PIX_FMT_YUVA422P16BE:
case AV_PIX_FMT_YUVA444P16BE:
c->chrToYV12 = bswap16UV_c;
break;
#endif
}
if (c->chrSrcHSubSample) {
switch (srcFormat) {
case AV_PIX_FMT_RGBA64BE:
c->chrToYV12 = rgb64BEToUV_half_c;
break;
case AV_PIX_FMT_RGBA64LE:
c->chrToYV12 = rgb64LEToUV_half_c;
break;
case AV_PIX_FMT_BGRA64BE:
c->chrToYV12 = bgr64BEToUV_half_c;
break;
case AV_PIX_FMT_BGRA64LE:
c->chrToYV12 = bgr64LEToUV_half_c;
break;
case AV_PIX_FMT_RGB48BE:
c->chrToYV12 = rgb48BEToUV_half_c;
break;
case AV_PIX_FMT_RGB48LE:
c->chrToYV12 = rgb48LEToUV_half_c;
break;
case AV_PIX_FMT_BGR48BE:
c->chrToYV12 = bgr48BEToUV_half_c;
break;
case AV_PIX_FMT_BGR48LE:
c->chrToYV12 = bgr48LEToUV_half_c;
break;
case AV_PIX_FMT_RGB32:
c->chrToYV12 = bgr32ToUV_half_c;
break;
case AV_PIX_FMT_RGB32_1:
c->chrToYV12 = bgr321ToUV_half_c;
break;
case AV_PIX_FMT_BGR24:
c->chrToYV12 = bgr24ToUV_half_c;
break;
case AV_PIX_FMT_BGR565LE:
c->chrToYV12 = bgr16leToUV_half_c;
break;
case AV_PIX_FMT_BGR565BE:
c->chrToYV12 = bgr16beToUV_half_c;
break;
case AV_PIX_FMT_BGR555LE:
c->chrToYV12 = bgr15leToUV_half_c;
break;
case AV_PIX_FMT_BGR555BE:
c->chrToYV12 = bgr15beToUV_half_c;
break;
case AV_PIX_FMT_GBRAP:
case AV_PIX_FMT_GBRP:
c->chrToYV12 = gbr24pToUV_half_c;
break;
case AV_PIX_FMT_BGR444LE:
c->chrToYV12 = bgr12leToUV_half_c;
break;
case AV_PIX_FMT_BGR444BE:
c->chrToYV12 = bgr12beToUV_half_c;
break;
case AV_PIX_FMT_BGR32:
c->chrToYV12 = rgb32ToUV_half_c;
break;
case AV_PIX_FMT_BGR32_1:
c->chrToYV12 = rgb321ToUV_half_c;
break;
case AV_PIX_FMT_RGB24:
c->chrToYV12 = rgb24ToUV_half_c;
break;
case AV_PIX_FMT_RGB565LE:
c->chrToYV12 = rgb16leToUV_half_c;
break;
case AV_PIX_FMT_RGB565BE:
c->chrToYV12 = rgb16beToUV_half_c;
break;
case AV_PIX_FMT_RGB555LE:
c->chrToYV12 = rgb15leToUV_half_c;
break;
case AV_PIX_FMT_RGB555BE:
c->chrToYV12 = rgb15beToUV_half_c;
break;
case AV_PIX_FMT_RGB444LE:
c->chrToYV12 = rgb12leToUV_half_c;
break;
case AV_PIX_FMT_RGB444BE:
c->chrToYV12 = rgb12beToUV_half_c;
break;
}
} else {
switch (srcFormat) {
case AV_PIX_FMT_RGBA64BE:
c->chrToYV12 = rgb64BEToUV_c;
break;
case AV_PIX_FMT_RGBA64LE:
c->chrToYV12 = rgb64LEToUV_c;
break;
case AV_PIX_FMT_BGRA64BE:
c->chrToYV12 = bgr64BEToUV_c;
break;
case AV_PIX_FMT_BGRA64LE:
c->chrToYV12 = bgr64LEToUV_c;
break;
case AV_PIX_FMT_RGB48BE:
c->chrToYV12 = rgb48BEToUV_c;
break;
case AV_PIX_FMT_RGB48LE:
c->chrToYV12 = rgb48LEToUV_c;
break;
case AV_PIX_FMT_BGR48BE:
c->chrToYV12 = bgr48BEToUV_c;
break;
case AV_PIX_FMT_BGR48LE:
c->chrToYV12 = bgr48LEToUV_c;
break;
case AV_PIX_FMT_RGB32:
c->chrToYV12 = bgr32ToUV_c;
break;
case AV_PIX_FMT_RGB32_1:
c->chrToYV12 = bgr321ToUV_c;
break;
case AV_PIX_FMT_BGR24:
c->chrToYV12 = bgr24ToUV_c;
break;
case AV_PIX_FMT_BGR565LE:
c->chrToYV12 = bgr16leToUV_c;
break;
case AV_PIX_FMT_BGR565BE:
c->chrToYV12 = bgr16beToUV_c;
break;
case AV_PIX_FMT_BGR555LE:
c->chrToYV12 = bgr15leToUV_c;
break;
case AV_PIX_FMT_BGR555BE:
c->chrToYV12 = bgr15beToUV_c;
break;
case AV_PIX_FMT_BGR444LE:
c->chrToYV12 = bgr12leToUV_c;
break;
case AV_PIX_FMT_BGR444BE:
c->chrToYV12 = bgr12beToUV_c;
break;
case AV_PIX_FMT_BGR32:
c->chrToYV12 = rgb32ToUV_c;
break;
case AV_PIX_FMT_BGR32_1:
c->chrToYV12 = rgb321ToUV_c;
break;
case AV_PIX_FMT_RGB24:
c->chrToYV12 = rgb24ToUV_c;
break;
case AV_PIX_FMT_RGB565LE:
c->chrToYV12 = rgb16leToUV_c;
break;
case AV_PIX_FMT_RGB565BE:
c->chrToYV12 = rgb16beToUV_c;
break;
case AV_PIX_FMT_RGB555LE:
c->chrToYV12 = rgb15leToUV_c;
break;
case AV_PIX_FMT_RGB555BE:
c->chrToYV12 = rgb15beToUV_c;
break;
case AV_PIX_FMT_RGB444LE:
c->chrToYV12 = rgb12leToUV_c;
break;
case AV_PIX_FMT_RGB444BE:
c->chrToYV12 = rgb12beToUV_c;
break;
}
}
c->lumToYV12 = NULL;
c->alpToYV12 = NULL;
switch (srcFormat) {
case AV_PIX_FMT_GBRP9LE:
c->readLumPlanar = planar_rgb9le_to_y;
break;
case AV_PIX_FMT_GBRP10LE:
c->readLumPlanar = planar_rgb10le_to_y;
break;
case AV_PIX_FMT_GBRP12LE:
c->readLumPlanar = planar_rgb12le_to_y;
break;
case AV_PIX_FMT_GBRP14LE:
c->readLumPlanar = planar_rgb14le_to_y;
break;
case AV_PIX_FMT_GBRAP16LE:
case AV_PIX_FMT_GBRP16LE:
c->readLumPlanar = planar_rgb16le_to_y;
break;
case AV_PIX_FMT_GBRP9BE:
c->readLumPlanar = planar_rgb9be_to_y;
break;
case AV_PIX_FMT_GBRP10BE:
c->readLumPlanar = planar_rgb10be_to_y;
break;
case AV_PIX_FMT_GBRP12BE:
c->readLumPlanar = planar_rgb12be_to_y;
break;
case AV_PIX_FMT_GBRP14BE:
c->readLumPlanar = planar_rgb14be_to_y;
break;
case AV_PIX_FMT_GBRAP16BE:
case AV_PIX_FMT_GBRP16BE:
c->readLumPlanar = planar_rgb16be_to_y;
break;
case AV_PIX_FMT_GBRAP:
c->readAlpPlanar = planar_rgb_to_a;
case AV_PIX_FMT_GBRP:
c->readLumPlanar = planar_rgb_to_y;
break;
#if HAVE_BIGENDIAN
case AV_PIX_FMT_YUV444P9LE:
case AV_PIX_FMT_YUV422P9LE:
case AV_PIX_FMT_YUV420P9LE:
case AV_PIX_FMT_YUV444P10LE:
case AV_PIX_FMT_YUV422P10LE:
case AV_PIX_FMT_YUV420P10LE:
case AV_PIX_FMT_YUV444P12LE:
case AV_PIX_FMT_YUV422P12LE:
case AV_PIX_FMT_YUV420P12LE:
case AV_PIX_FMT_YUV444P14LE:
case AV_PIX_FMT_YUV422P14LE:
case AV_PIX_FMT_YUV420P14LE:
case AV_PIX_FMT_YUV420P16LE:
case AV_PIX_FMT_YUV422P16LE:
case AV_PIX_FMT_YUV444P16LE:
case AV_PIX_FMT_GRAY16LE:
c->lumToYV12 = bswap16Y_c;
break;
case AV_PIX_FMT_YUVA444P9LE:
case AV_PIX_FMT_YUVA422P9LE:
case AV_PIX_FMT_YUVA420P9LE:
case AV_PIX_FMT_YUVA444P10LE:
case AV_PIX_FMT_YUVA422P10LE:
case AV_PIX_FMT_YUVA420P10LE:
case AV_PIX_FMT_YUVA420P16LE:
case AV_PIX_FMT_YUVA422P16LE:
case AV_PIX_FMT_YUVA444P16LE:
c->lumToYV12 = bswap16Y_c;
c->alpToYV12 = bswap16Y_c;
break;
#else
case AV_PIX_FMT_YUV444P9BE:
case AV_PIX_FMT_YUV422P9BE:
case AV_PIX_FMT_YUV420P9BE:
case AV_PIX_FMT_YUV444P10BE:
case AV_PIX_FMT_YUV422P10BE:
case AV_PIX_FMT_YUV420P10BE:
case AV_PIX_FMT_YUV444P12BE:
case AV_PIX_FMT_YUV422P12BE:
case AV_PIX_FMT_YUV420P12BE:
case AV_PIX_FMT_YUV444P14BE:
case AV_PIX_FMT_YUV422P14BE:
case AV_PIX_FMT_YUV420P14BE:
case AV_PIX_FMT_YUV420P16BE:
case AV_PIX_FMT_YUV422P16BE:
case AV_PIX_FMT_YUV444P16BE:
case AV_PIX_FMT_GRAY16BE:
c->lumToYV12 = bswap16Y_c;
break;
case AV_PIX_FMT_YUVA444P9BE:
case AV_PIX_FMT_YUVA422P9BE:
case AV_PIX_FMT_YUVA420P9BE:
case AV_PIX_FMT_YUVA444P10BE:
case AV_PIX_FMT_YUVA422P10BE:
case AV_PIX_FMT_YUVA420P10BE:
case AV_PIX_FMT_YUVA420P16BE:
case AV_PIX_FMT_YUVA422P16BE:
case AV_PIX_FMT_YUVA444P16BE:
c->lumToYV12 = bswap16Y_c;
c->alpToYV12 = bswap16Y_c;
break;
#endif
case AV_PIX_FMT_YA16LE:
c->lumToYV12 = read_ya16le_gray_c;
c->alpToYV12 = read_ya16le_alpha_c;
break;
case AV_PIX_FMT_YA16BE:
c->lumToYV12 = read_ya16be_gray_c;
c->alpToYV12 = read_ya16be_alpha_c;
break;
case AV_PIX_FMT_YUYV422:
case AV_PIX_FMT_YVYU422:
case AV_PIX_FMT_YA8:
c->lumToYV12 = yuy2ToY_c;
break;
case AV_PIX_FMT_UYVY422:
c->lumToYV12 = uyvyToY_c;
break;
case AV_PIX_FMT_BGR24:
c->lumToYV12 = bgr24ToY_c;
break;
case AV_PIX_FMT_BGR565LE:
c->lumToYV12 = bgr16leToY_c;
break;
case AV_PIX_FMT_BGR565BE:
c->lumToYV12 = bgr16beToY_c;
break;
case AV_PIX_FMT_BGR555LE:
c->lumToYV12 = bgr15leToY_c;
break;
case AV_PIX_FMT_BGR555BE:
c->lumToYV12 = bgr15beToY_c;
break;
case AV_PIX_FMT_BGR444LE:
c->lumToYV12 = bgr12leToY_c;
break;
case AV_PIX_FMT_BGR444BE:
c->lumToYV12 = bgr12beToY_c;
break;
case AV_PIX_FMT_RGB24:
c->lumToYV12 = rgb24ToY_c;
break;
case AV_PIX_FMT_RGB565LE:
c->lumToYV12 = rgb16leToY_c;
break;
case AV_PIX_FMT_RGB565BE:
c->lumToYV12 = rgb16beToY_c;
break;
case AV_PIX_FMT_RGB555LE:
c->lumToYV12 = rgb15leToY_c;
break;
case AV_PIX_FMT_RGB555BE:
c->lumToYV12 = rgb15beToY_c;
break;
case AV_PIX_FMT_RGB444LE:
c->lumToYV12 = rgb12leToY_c;
break;
case AV_PIX_FMT_RGB444BE:
c->lumToYV12 = rgb12beToY_c;
break;
case AV_PIX_FMT_RGB8:
case AV_PIX_FMT_BGR8:
case AV_PIX_FMT_PAL8:
case AV_PIX_FMT_BGR4_BYTE:
case AV_PIX_FMT_RGB4_BYTE:
c->lumToYV12 = palToY_c;
break;
case AV_PIX_FMT_MONOBLACK:
c->lumToYV12 = monoblack2Y_c;
break;
case AV_PIX_FMT_MONOWHITE:
c->lumToYV12 = monowhite2Y_c;
break;
case AV_PIX_FMT_RGB32:
c->lumToYV12 = bgr32ToY_c;
break;
case AV_PIX_FMT_RGB32_1:
c->lumToYV12 = bgr321ToY_c;
break;
case AV_PIX_FMT_BGR32:
c->lumToYV12 = rgb32ToY_c;
break;
case AV_PIX_FMT_BGR32_1:
c->lumToYV12 = rgb321ToY_c;
break;
case AV_PIX_FMT_RGB48BE:
c->lumToYV12 = rgb48BEToY_c;
break;
case AV_PIX_FMT_RGB48LE:
c->lumToYV12 = rgb48LEToY_c;
break;
case AV_PIX_FMT_BGR48BE:
c->lumToYV12 = bgr48BEToY_c;
break;
case AV_PIX_FMT_BGR48LE:
c->lumToYV12 = bgr48LEToY_c;
break;
case AV_PIX_FMT_RGBA64BE:
c->lumToYV12 = rgb64BEToY_c;
break;
case AV_PIX_FMT_RGBA64LE:
c->lumToYV12 = rgb64LEToY_c;
break;
case AV_PIX_FMT_BGRA64BE:
c->lumToYV12 = bgr64BEToY_c;
break;
case AV_PIX_FMT_BGRA64LE:
c->lumToYV12 = bgr64LEToY_c;
}
if (c->alpPixBuf) {
if (is16BPS(srcFormat) || isNBPS(srcFormat)) {
if (HAVE_BIGENDIAN == !isBE(srcFormat))
c->alpToYV12 = bswap16Y_c;
}
switch (srcFormat) {
case AV_PIX_FMT_BGRA64LE:
case AV_PIX_FMT_BGRA64BE:
case AV_PIX_FMT_RGBA64LE:
case AV_PIX_FMT_RGBA64BE: c->alpToYV12 = rgba64ToA_c; break;
case AV_PIX_FMT_BGRA:
case AV_PIX_FMT_RGBA:
c->alpToYV12 = rgbaToA_c;
break;
case AV_PIX_FMT_ABGR:
case AV_PIX_FMT_ARGB:
c->alpToYV12 = abgrToA_c;
break;
case AV_PIX_FMT_YA8:
c->alpToYV12 = uyvyToY_c;
break;
case AV_PIX_FMT_PAL8 :
c->alpToYV12 = palToA_c;
break;
}
}
}

ff_sws_init_input_funcs()根据输入像素格式的不同，对以下几个函数指针进行赋值：

lumToYV12：转换得到Y分量。
chrToYV12：转换得到UV分量。
alpToYV12：转换得到Alpha分量。
readLumPlanar：读取planar格式的数据转换为Y。
readChrPlanar：读取planar格式的数据转换为UV。

下面看几个例子。

当输入像素格式为AV_PIX_FMT_RGB24的时候，lumToYV12()指针指向的函数是rgb24ToY_c()，如下所示。

[cpp] view plaincopy

case AV_PIX_FMT_RGB24:
c->lumToYV12 = rgb24ToY_c;
break;

rgb24ToY_c()

rgb24ToY_c()的定义如下。

[cpp] view plaincopy

static void rgb24ToY_c(uint8_t *_dst, const uint8_t *src, const uint8_t *unused1, const uint8_t *unused2, int width,
uint32_t *rgb2yuv)
{
int16_t *dst = (int16_t *)_dst;
int32_t ry = rgb2yuv[RY_IDX], gy = rgb2yuv[GY_IDX], by = rgb2yuv[BY_IDX];
int i;
for (i = 0; i < width; i++) {
int r = src[i * 3 + 0];
int g = src[i * 3 + 1];
int b = src[i * 3 + 2];
dst[i] = ((ry*r + gy*g + by*b + (32<<(RGB2YUV_SHIFT-1)) + (1<<(RGB2YUV_SHIFT-7)))>>(RGB2YUV_SHIFT-6));
}
}

从源代码中可以看出，该函数主要完成了以下三步：

1. 取系数。通过读取rgb2yuv数组中存储的参数获得R，G，B每个分量的系数。
2. 取像素值。分别读取R，G，B每个分量的像素值。
3. 计算得到亮度值。根据R，G，B的系数和值，计算得到亮度值Y。

当输入像素格式为AV_PIX_FMT_RGB24的时候，chrToYV12 ()指针指向的函数是rgb24ToUV_half_c()，如下所示。

[cpp] view plaincopy

case AV_PIX_FMT_RGB24:
c->chrToYV12 = rgb24ToUV_half_c;
break;

rgb24ToUV_half_c()

rgb24ToUV_half_c()定义如下。

[cpp] view plaincopy

static void rgb24ToUV_half_c(uint8_t *_dstU, uint8_t *_dstV, const uint8_t *unused0, const uint8_t *src1,
const uint8_t *src2, int width, uint32_t *rgb2yuv)
{
int16_t *dstU = (int16_t *)_dstU;
int16_t *dstV = (int16_t *)_dstV;
int i;
int32_t ru = rgb2yuv[RU_IDX], gu = rgb2yuv[GU_IDX], bu = rgb2yuv[BU_IDX];
int32_t rv = rgb2yuv[RV_IDX], gv = rgb2yuv[GV_IDX], bv = rgb2yuv[BV_IDX];
av_assert1(src1 == src2);
for (i = 0; i < width; i++) {
int r = src1[6 * i + 0] + src1[6 * i + 3];
int g = src1[6 * i + 1] + src1[6 * i + 4];
int b = src1[6 * i + 2] + src1[6 * i + 5];
dstU[i] = (ru*r + gu*g + bu*b + (256<<RGB2YUV_SHIFT) + (1<<(RGB2YUV_SHIFT-6)))>>(RGB2YUV_SHIFT-5);
dstV[i] = (rv*r + gv*g + bv*b + (256<<RGB2YUV_SHIFT) + (1<<(RGB2YUV_SHIFT-6)))>>(RGB2YUV_SHIFT-5);
}
}

rgb24ToUV_half_c()的过程相比rgb24ToY_c()要稍微复杂些。这主要是因为U，V取值的数量只有Y的一半。因此需要首先求出每2个像素点的平均值之后，再进行计算。
当输入像素格式为AV_PIX_FMT_GBRP（注意这个是planar格式，三个分量分别为G，B，R）的时候，readLumPlanar指向的函数是planar_rgb_to_y()，如下所示。

[cpp] view plaincopy

case AV_PIX_FMT_GBRP:
c->readLumPlanar = planar_rgb_to_y;
break;

planar_rgb_to_y()

planar_rgb_to_y()定义如下。

[cpp] view plaincopy

static void planar_rgb_to_y(uint8_t *_dst, const uint8_t *src[4], int width, int32_t *rgb2yuv)
{
uint16_t *dst = (uint16_t *)_dst;
int32_t ry = rgb2yuv[RY_IDX], gy = rgb2yuv[GY_IDX], by = rgb2yuv[BY_IDX];
int i;
for (i = 0; i < width; i++) {
int g = src[0][i];
int b = src[1][i];
int r = src[2][i];
dst[i] = (ry*r + gy*g + by*b + (0x801<<(RGB2YUV_SHIFT-7))) >> (RGB2YUV_SHIFT-6);
}
}

可以看出处理planar格式的GBR数据和处理packed格式的RGB数据的方法是基本一样的，在这里不再重复。

ff_sws_init_range_convert()

ff_sws_init_range_convert()用于初始化像素值范围转换的函数，它的定义位于libswscale\swscale.c，如下所示。

[cpp] view plaincopy

av_cold void ff_sws_init_range_convert(SwsContext *c)
{
c->lumConvertRange = NULL;
c->chrConvertRange = NULL;
if (c->srcRange != c->dstRange && !isAnyRGB(c->dstFormat)) {
if (c->dstBpc <= 14) {
if (c->srcRange) {
c->lumConvertRange = lumRangeFromJpeg_c;
c->chrConvertRange = chrRangeFromJpeg_c;
} else {
c->lumConvertRange = lumRangeToJpeg_c;
c->chrConvertRange = chrRangeToJpeg_c;
}
} else {
if (c->srcRange) {
c->lumConvertRange = lumRangeFromJpeg16_c;
c->chrConvertRange = chrRangeFromJpeg16_c;
} else {
c->lumConvertRange = lumRangeToJpeg16_c;
c->chrConvertRange = chrRangeToJpeg16_c;
}
}
}
}

ff_sws_init_range_convert()包含了两种像素取值范围的转换：

lumConvertRange：亮度分量取值范围的转换。
chrConvertRange：色度分量取值范围的转换。

从JPEG标准转换为MPEG标准的函数有：lumRangeFromJpeg_c()和chrRangeFromJpeg_c()。

lumRangeFromJpeg_c()

亮度转换（0-255转换为16-235）函数lumRangeFromJpeg_c()如下所示。

[cpp] view plaincopy

static void lumRangeFromJpeg_c(int16_t *dst, int width)
{
int i;
for (i = 0; i < width; i++)
dst[i] = (dst[i] * 14071 + 33561947) >> 14;
}

可以简单代入一个数字验证一下上述函数的正确性。该函数将亮度值“0”映射成“16”，“255”映射成“235”，因此我们可以代入一个“255”看看转换后的数值是否为“235”。在这里需要注意，dst中存储的像素数值是15bit的亮度值。因此我们需要将8bit的数值“255”左移7位后带入。经过计算，255左移7位后取值为32640，计算后得到的数值为30080，右移7位后得到的8bit亮度值即为235。

后续几个函数都可以用上面描述的方法进行验证，就不再重复了。

chrRangeFromJpeg_c()

色度转换（0-255转换为16-240）函数chrRangeFromJpeg_c()如下所示。

[cpp] view plaincopy

static void chrRangeFromJpeg_c(int16_t *dstU, int16_t *dstV, int width)
{
int i;
for (i = 0; i < width; i++) {
dstU[i] = (dstU[i] * 1799 + 4081085) >> 11; // 1469
dstV[i] = (dstV[i] * 1799 + 4081085) >> 11; // 1469
}
}

从MPEG标准转换为JPEG标准的函数有：lumRangeToJpeg_c()和chrRangeToJpeg_c()。

lumRangeToJpeg_c()

亮度转换（16-235转换为0-255）函数lumRangeToJpeg_c()定义如下所示。

[cpp] view plaincopy

static void lumRangeToJpeg_c(int16_t *dst, int width)
{
int i;
for (i = 0; i < width; i++)
dst[i] = (FFMIN(dst[i], 30189) * 19077 - 39057361) >> 14;
}

chrRangeToJpeg_c()

色度转换（16-240转换为0-255）函数chrRangeToJpeg_c()定义如下所示。

[cpp] view plaincopy

static void chrRangeToJpeg_c(int16_t *dstU, int16_t *dstV, int width)
{
int i;
for (i = 0; i < width; i++) {
dstU[i] = (FFMIN(dstU[i], 30775) * 4663 - 9289992) >> 12; // -264
dstV[i] = (FFMIN(dstV[i], 30775) * 4663 - 9289992) >> 12; // -264
}
}

至此sws_getContext()的源代码就基本上分析完毕了。

雷霄骅
leixiaohua1020@126.com
http://blog.csdn.net/leixiaohua1020