FFmpeg总结（二）AV系列结构体之AVFrame

位于libavutil下frame.h文件中

这个结构体用来描述解码出音视频数据。
AVFrame必须使用av_frame_alloc分配()。
AVFrame必须与av_frame_free释放()。
AVFrame通常分配一次,然后重复使用多次，不同的数据（如一个AVFrame持有来自解码器的frames。)在再次使用时,av_frame_unref()将自由持有的任何之前的帧引用并重置它变成初始态。
一个AVFrame所描述的数据通常是通过参考AVBuffer API计算。内部的buffer引用存储在AVFrame.buf /AVFrame.extended_buf。
AVFrame将用于引用计数,当至少一个引用被set时,如果AVFrame.buf[0] != NULL, 每个单个数据至少包含一个AVFrame.buf /AVFrame.extended_buf.可能会有一个缓冲的数据,或一个单独的缓冲对每个plane, 或介于两者之间的任何东西。
sizeof(AVFrame)不是一个public的API,因此新的成员将被添加到末尾。同样字段标记为只访问av_opt_ptr()可以重新排序


typedef struct AVFrame {
#define AV_NUM_DATA_POINTERS 8/*** pointer to the picture/channel planes.* This might be different from the first allocated byte** Some decoders access areas outside 0,0 - width,height, please* see avcodec_align_dimensions2(). Some filters and swscale can read* up to 16 bytes beyond the planes, if these filters are to be used,* then 16 extra bytes must be allocated.** NOTE: Except for hwaccel formats, pointers not needed by the format* MUST be set to NULL.*/uint8_t *data[AV_NUM_DATA_POINTERS];/*** For video, size in bytes of each picture line.* For audio, size in bytes of each plane.** For audio, only linesize[0] may be set. For planar audio, each channel* plane must be the same size.** For video the linesizes should be multiples of the CPUs alignment* preference, this is 16 or 32 for modern desktop CPUs.* Some code requires such alignment other code can be slower without* correct alignment, for yet other it makes no difference.** @note The linesize may be larger than the size of usable data -- there* may be extra padding present for performance reasons.*/int linesize[AV_NUM_DATA_POINTERS];/*** pointers to the data planes/channels.** For video, this should simply point to data[].** For planar audio, each channel has a separate data pointer, and* linesize[0] contains the size of each channel buffer.* For packed audio, there is just one data pointer, and linesize[0]* contains the total size of the buffer for all channels.** Note: Both data and extended_data should always be set in a valid frame,* but for planar audio with more channels that can fit in data,* extended_data must be used in order to access all channels.*/uint8_t **extended_data;/*** width and height of the video frame*/int width, height;/*** number of audio samples (per channel) described by this frame*/int nb_samples;/*** format of the frame, -1 if unknown or unset* Values correspond to enum AVPixelFormat for video frames,* enum AVSampleFormat for audio)*/int format;/*** 1 -> keyframe, 0-> not*/int key_frame;/*** Picture type of the frame.*/enum AVPictureType pict_type;/*** Sample aspect ratio for the video frame, 0/1 if unknown/unspecified.*/AVRational sample_aspect_ratio;/*** Presentation timestamp in time_base units (time when frame should be shown to user).*/int64_t pts;/*** PTS copied from the AVPacket that was decoded to produce this frame.*/int64_t pkt_pts;/*** DTS copied from the AVPacket that triggered returning this frame. (if frame threading isn't used)* This is also the Presentation time of this AVFrame calculated from* only AVPacket.dts values without pts values.*/int64_t pkt_dts;/*** picture number in bitstream order*/int coded_picture_number;/*** picture number in display order*/int display_picture_number;/*** quality (between 1 (good) and FF_LAMBDA_MAX (bad))*/int quality;/*** for some private data of the user*/void *opaque;#if FF_API_ERROR_FRAME/*** @deprecated unused*/attribute_deprecateduint64_t error[AV_NUM_DATA_POINTERS];
#endif/*** When decoding, this signals how much the picture must be delayed.* extra_delay = repeat_pict / (2*fps)*/int repeat_pict;/*** The content of the picture is interlaced.*/int interlaced_frame;/*** If the content is interlaced, is top field displayed first.*/int top_field_first;/*** Tell user application that palette has changed from previous frame.*/int palette_has_changed;/*** reordered opaque 64 bits (generally an integer or a double precision float* PTS but can be anything).* The user sets AVCodecContext.reordered_opaque to represent the input at* that time,* the decoder reorders values as needed and sets AVFrame.reordered_opaque* to exactly one of the values provided by the user through AVCodecContext.reordered_opaque* @deprecated in favor of pkt_pts*/int64_t reordered_opaque;/*** Sample rate of the audio data.*/int sample_rate;/*** Channel layout of the audio data.*/uint64_t channel_layout;/*** AVBuffer references backing the data for this frame. If all elements of* this array are NULL, then this frame is not reference counted. This array* must be filled contiguously -- if buf[i] is non-NULL then buf[j] must* also be non-NULL for all j < i.** There may be at most one AVBuffer per data plane, so for video this array* always contains all the references. For planar audio with more than* AV_NUM_DATA_POINTERS channels, there may be more buffers than can fit in* this array. Then the extra AVBufferRef pointers are stored in the* extended_buf array.*/AVBufferRef *buf[AV_NUM_DATA_POINTERS];/*** For planar audio which requires more than AV_NUM_DATA_POINTERS* AVBufferRef pointers, this array will hold all the references which* cannot fit into AVFrame.buf.** Note that this is different from AVFrame.extended_data, which always* contains all the pointers. This array only contains the extra pointers,* which cannot fit into AVFrame.buf.** This array is always allocated using av_malloc() by whoever constructs* the frame. It is freed in av_frame_unref().*/AVBufferRef **extended_buf;/*** Number of elements in extended_buf.*/int        nb_extended_buf;AVFrameSideData **side_data;int            nb_side_data;/*** @defgroup lavu_frame_flags AV_FRAME_FLAGS* Flags describing additional frame properties.** @{*//*** The frame data may be corrupted, e.g. due to decoding errors.*/
#define AV_FRAME_FLAG_CORRUPT       (1 << 0)
/*** @}*//*** Frame flags, a combination of @ref lavu_frame_flags*/int flags;/*** MPEG vs JPEG YUV range.* It must be accessed using av_frame_get_color_range() and* av_frame_set_color_range().* - encoding: Set by user* - decoding: Set by libavcodec*/enum AVColorRange color_range;enum AVColorPrimaries color_primaries;enum AVColorTransferCharacteristic color_trc;/*** YUV colorspace type.* It must be accessed using av_frame_get_colorspace() and* av_frame_set_colorspace().* - encoding: Set by user* - decoding: Set by libavcodec*/enum AVColorSpace colorspace;enum AVChromaLocation chroma_location;/*** frame timestamp estimated using various heuristics, in stream time base* Code outside libavutil should access this field using:* av_frame_get_best_effort_timestamp(frame)* - encoding: unused* - decoding: set by libavcodec, read by user.*/int64_t best_effort_timestamp;/*** reordered pos from the last AVPacket that has been input into the decoder* Code outside libavutil should access this field using:* av_frame_get_pkt_pos(frame)* - encoding: unused* - decoding: Read by user.*/int64_t pkt_pos;/*** duration of the corresponding packet, expressed in* AVStream->time_base units, 0 if unknown.* Code outside libavutil should access this field using:* av_frame_get_pkt_duration(frame)* - encoding: unused* - decoding: Read by user.*/int64_t pkt_duration;/*** metadata.* Code outside libavutil should access this field using:* av_frame_get_metadata(frame)* - encoding: Set by user.* - decoding: Set by libavcodec.*/AVDictionary *metadata;/*** decode error flags of the frame, set to a combination of* FF_DECODE_ERROR_xxx flags if the decoder produced a frame, but there* were errors during the decoding.* Code outside libavutil should access this field using:* av_frame_get_decode_error_flags(frame)* - encoding: unused* - decoding: set by libavcodec, read by user.*/int decode_error_flags;
#define FF_DECODE_ERROR_INVALID_BITSTREAM   1
#define FF_DECODE_ERROR_MISSING_REFERENCE   2/*** number of audio channels, only used for audio.* Code outside libavutil should access this field using:* av_frame_get_channels(frame)* - encoding: unused* - decoding: Read by user.*/int channels;/*** size of the corresponding packet containing the compressed* frame. It must be accessed using av_frame_get_pkt_size() and* av_frame_set_pkt_size().* It is set to a negative value if unknown.* - encoding: unused* - decoding: set by libavcodec, read by user.*/int pkt_size;#if FF_API_FRAME_QP/*** QP table* Not to be accessed directly from outside libavutil*/attribute_deprecatedint8_t *qscale_table;/*** QP store stride* Not to be accessed directly from outside libavutil*/attribute_deprecatedint qstride;attribute_deprecatedint qscale_type;/*** Not to be accessed directly from outside libavutil*/AVBufferRef *qp_table_buf;
#endif/*** For hwaccel-format frames, this should be a reference to the* AVHWFramesContext describing the frame.*/AVBufferRef *hw_frames_ctx;
} AVFrame;

uint8_t *data[AV_NUM_DATA_POINTERS]：指针数组，存放YUV数据的地方。如图所示，一般占用前3个指针，分别指向Y，U，V数据。
- 对于packed格式的数据（例如RGB24），会存到data[0]里面。
  对于planar格式的数据（例如YUV420P），则会分开成data[0]，data[1]，data[2]…（YUV420P中data[0]存Y，data[1]存U，data[2]存V）
int linesize[AV_NUM_DATA_POINTERS]：图像各个分量数据在此结构体中的的宽度。注意这并不是图像的宽度。在此例子中图像的尺寸为672X272，而亮度分量的宽度为704，应该是图像宽度经过64对齐后的结果。
uint8_t **extended_data：指向了图像数据。
int width, height：图像的宽高。
int nb_samples：此帧音频的点数。
int format：像素类型（视频），样点类型（音频）
int key_frame：是否关键帧，此例中为视频的第一帧，当然是关键帧了。
enum AVPictureType pict_type：图像类型，I，P，B等，同样，第一帧是I帧。
AVRational sample_aspect_ratio：像素的宽高比，注意不是图像的。
int64_t pts，pkt_pts，pkt_dts：和时间戳有关的变量，以后会详细介绍。
int coded_picture_number：编码顺序的图像num。
int display_picture_number：播放顺序的图像num。
int interlaced_frame：图像是否是隔行的。
int top_field_first：图像的top field first变量。
int64_t pkt_duration：对应packet的显示时长。
int pkt_size：对应packet的尺寸。
int8_t *qscale_table：据推测是存放qp（量化参数）的数组
AVBufferRef *qp_table_buf：成员data指向qscale_table。

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