FFMPEG结构体分析：AVCodecContext
2024-05-20 05:33:52
注：写了一系列的结构体的分析的文章，在这里列一个列表：
FFMPEG结构体分析：AVFrame
FFMPEG结构体分析：AVFormatContext
FFMPEG结构体分析：AVCodecContext
FFMPEG结构体分析：AVIOContext
FFMPEG结构体分析：AVCodec
FFMPEG结构体分析：AVStream
FFMPEG结构体分析：AVPacket
FFMPEG有几个最重要的结构体，包含了解协议，解封装，解码操作，此前已经进行过分析：
FFMPEG中最关键的结构体之间的关系
在此不再详述，其中AVCodecContext是包含变量较多的结构体（感觉差不多是变量最多的结构体）。本文将会大概分析一下该结构体里每个变量的含义和作用。因为如果每个变量都分析的话，工作量太大，实在来不及。
首先看一下结构体的定义（位于avcodec.h）：
/**雷霄骅*leixiaohua1020@126.com*中国传媒大学/数字电视技术*/
/*** main external API structure.* New fields can be added to the end with minor version bumps.* Removal, reordering and changes to existing fields require a major* version bump.* Please use AVOptions (av_opt* / av_set/get*()) to access these fields from user* applications.* sizeof(AVCodecContext) must not be used outside libav*.*/
typedef struct AVCodecContext {/*** information on struct for av_log* - set by avcodec_alloc_context3*/const AVClass *av_class;int log_level_offset;enum AVMediaType codec_type; /* see AVMEDIA_TYPE_xxx */const struct AVCodec *codec;char codec_name[32];enum AVCodecID codec_id; /* see AV_CODEC_ID_xxx *//*** fourcc (LSB first, so "ABCD" -> ('D'<<24) + ('C'<<16) + ('B'<<8) + 'A').* This is used to work around some encoder bugs.* A demuxer should set this to what is stored in the field used to identify the codec.* If there are multiple such fields in a container then the demuxer should choose the one* which maximizes the information about the used codec.* If the codec tag field in a container is larger than 32 bits then the demuxer should* remap the longer ID to 32 bits with a table or other structure. Alternatively a new* extra_codec_tag + size could be added but for this a clear advantage must be demonstrated* first.* - encoding: Set by user, if not then the default based on codec_id will be used.* - decoding: Set by user, will be converted to uppercase by libavcodec during init.*/unsigned int codec_tag;/*** fourcc from the AVI stream header (LSB first, so "ABCD" -> ('D'<<24) + ('C'<<16) + ('B'<<8) + 'A').* This is used to work around some encoder bugs.* - encoding: unused* - decoding: Set by user, will be converted to uppercase by libavcodec during init.*/unsigned int stream_codec_tag;#if FF_API_SUB_ID/*** @deprecated this field is unused*/attribute_deprecated int sub_id;
#endifvoid *priv_data;/*** Private context used for internal data.** Unlike priv_data, this is not codec-specific. It is used in general* libavcodec functions.*/struct AVCodecInternal *internal;/*** Private data of the user, can be used to carry app specific stuff.* - encoding: Set by user.* - decoding: Set by user.*/void *opaque;/*** the average bitrate* - encoding: Set by user; unused for constant quantizer encoding.* - decoding: Set by libavcodec. 0 or some bitrate if this info is available in the stream.*/int bit_rate;/*** number of bits the bitstream is allowed to diverge from the reference.* the reference can be CBR (for CBR pass1) or VBR (for pass2)* - encoding: Set by user; unused for constant quantizer encoding.* - decoding: unused*/int bit_rate_tolerance;/*** Global quality for codecs which cannot change it per frame.* This should be proportional to MPEG-1/2/4 qscale.* - encoding: Set by user.* - decoding: unused*/int global_quality;/*** - encoding: Set by user.* - decoding: unused*/int compression_level;
#define FF_COMPRESSION_DEFAULT -1/*** CODEC_FLAG_*.* - encoding: Set by user.* - decoding: Set by user.*/int flags;/*** CODEC_FLAG2_** - encoding: Set by user.* - decoding: Set by user.*/int flags2;/*** some codecs need / can use extradata like Huffman tables.* mjpeg: Huffman tables* rv10: additional flags* mpeg4: global headers (they can be in the bitstream or here)* The allocated memory should be FF_INPUT_BUFFER_PADDING_SIZE bytes larger* than extradata_size to avoid prolems if it is read with the bitstream reader.* The bytewise contents of extradata must not depend on the architecture or CPU endianness.* - encoding: Set/allocated/freed by libavcodec.* - decoding: Set/allocated/freed by user.*/uint8_t *extradata;int extradata_size;/*** This is the fundamental unit of time (in seconds) in terms* of which frame timestamps are represented. For fixed-fps content,* timebase should be 1/framerate and timestamp increments should be* identically 1.* - encoding: MUST be set by user.* - decoding: Set by libavcodec.*/AVRational time_base;/*** For some codecs, the time base is closer to the field rate than the frame rate.* Most notably, H.264 and MPEG-2 specify time_base as half of frame duration* if no telecine is used ...** Set to time_base ticks per frame. Default 1, e.g., H.264/MPEG-2 set it to 2.*/int ticks_per_frame;/*** Encoding: Number of frames delay there will be from the encoder input to* the decoder output. (we assume the decoder matches the spec)* Decoding: Number of frames delay in addition to what a standard decoder* as specified in the spec would produce.** Video:* Number of frames the decoded output will be delayed relative to the* encoded input.** Audio:* For encoding, this is the number of "priming" samples added to the* beginning of the stream. The decoded output will be delayed by this* many samples relative to the input to the encoder. Note that this* field is purely informational and does not directly affect the pts* output by the encoder, which should always be based on the actual* presentation time, including any delay.* For decoding, this is the number of samples the decoder needs to* output before the decoder's output is valid. When seeking, you should* start decoding this many samples prior to your desired seek point.** - encoding: Set by libavcodec.* - decoding: Set by libavcodec.*/int delay;/* video only *//*** picture width / height.* - encoding: MUST be set by user.* - decoding: Set by libavcodec.* Note: For compatibility it is possible to set this instead of* coded_width/height before decoding.*/int width, height;/*** Bitstream width / height, may be different from width/height if lowres enabled.* - encoding: unused* - decoding: Set by user before init if known. Codec should override / dynamically change if needed.*/int coded_width, coded_height;#define FF_ASPECT_EXTENDED 15/*** the number of pictures in a group of pictures, or 0 for intra_only* - encoding: Set by user.* - decoding: unused*/int gop_size;/*** Pixel format, see AV_PIX_FMT_xxx.* May be set by the demuxer if known from headers.* May be overridden by the decoder if it knows better.* - encoding: Set by user.* - decoding: Set by user if known, overridden by libavcodec if known*/enum AVPixelFormat pix_fmt;/*** Motion estimation algorithm used for video coding.* 1 (zero), 2 (full), 3 (log), 4 (phods), 5 (epzs), 6 (x1), 7 (hex),* 8 (umh), 9 (iter), 10 (tesa) [7, 8, 10 are x264 specific, 9 is snow specific]* - encoding: MUST be set by user.* - decoding: unused*/int me_method;/*** If non NULL, 'draw_horiz_band' is called by the libavcodec* decoder to draw a horizontal band. It improves cache usage. Not* all codecs can do that. You must check the codec capabilities* beforehand.* When multithreading is used, it may be called from multiple threads* at the same time; threads might draw different parts of the same AVFrame,* or multiple AVFrames, and there is no guarantee that slices will be drawn* in order.* The function is also used by hardware acceleration APIs.* It is called at least once during frame decoding to pass* the data needed for hardware render.* In that mode instead of pixel data, AVFrame points to* a structure specific to the acceleration API. The application* reads the structure and can change some fields to indicate progress* or mark state.* - encoding: unused* - decoding: Set by user.* @param height the height of the slice* @param y the y position of the slice* @param type 1->top field, 2->bottom field, 3->frame* @param offset offset into the AVFrame.data from which the slice should be read*/void (*draw_horiz_band)(struct AVCodecContext *s,const AVFrame *src, int offset[AV_NUM_DATA_POINTERS],int y, int type, int height);/*** callback to negotiate the pixelFormat* @param fmt is the list of formats which are supported by the codec,* it is terminated by -1 as 0 is a valid format, the formats are ordered by quality.* The first is always the native one.* @return the chosen format* - encoding: unused* - decoding: Set by user, if not set the native format will be chosen.*/enum AVPixelFormat (*get_format)(struct AVCodecContext *s, const enum AVPixelFormat * fmt);/*** maximum number of B-frames between non-B-frames* Note: The output will be delayed by max_b_frames+1 relative to the input.* - encoding: Set by user.* - decoding: unused*/int max_b_frames;/*** qscale factor between IP and B-frames* If > 0 then the last P-frame quantizer will be used (q= lastp_q*factor+offset).* If < 0 then normal ratecontrol will be done (q= -normal_q*factor+offset).* - encoding: Set by user.* - decoding: unused*/float b_quant_factor;/** obsolete FIXME remove */int rc_strategy;
#define FF_RC_STRATEGY_XVID 1int b_frame_strategy;#if FF_API_MPV_GLOBAL_OPTS/*** luma single coefficient elimination threshold* - encoding: Set by user.* - decoding: unused*/attribute_deprecated int luma_elim_threshold;/*** chroma single coeff elimination threshold* - encoding: Set by user.* - decoding: unused*/attribute_deprecated int chroma_elim_threshold;
#endif/*** qscale offset between IP and B-frames* - encoding: Set by user.* - decoding: unused*/float b_quant_offset;/*** Size of the frame reordering buffer in the decoder.* For MPEG-2 it is 1 IPB or 0 low delay IP.* - encoding: Set by libavcodec.* - decoding: Set by libavcodec.*/int has_b_frames;/*** 0-> h263 quant 1-> mpeg quant* - encoding: Set by user.* - decoding: unused*/int mpeg_quant;/*** qscale factor between P and I-frames* If > 0 then the last p frame quantizer will be used (q= lastp_q*factor+offset).* If < 0 then normal ratecontrol will be done (q= -normal_q*factor+offset).* - encoding: Set by user.* - decoding: unused*/float i_quant_factor;/*** qscale offset between P and I-frames* - encoding: Set by user.* - decoding: unused*/float i_quant_offset;/*** luminance masking (0-> disabled)* - encoding: Set by user.* - decoding: unused*/float lumi_masking;/*** temporary complexity masking (0-> disabled)* - encoding: Set by user.* - decoding: unused*/float temporal_cplx_masking;/*** spatial complexity masking (0-> disabled)* - encoding: Set by user.* - decoding: unused*/float spatial_cplx_masking;/*** p block masking (0-> disabled)* - encoding: Set by user.* - decoding: unused*/float p_masking;/*** darkness masking (0-> disabled)* - encoding: Set by user.* - decoding: unused*/float dark_masking;/*** slice count* - encoding: Set by libavcodec.* - decoding: Set by user (or 0).*/int slice_count;/*** prediction method (needed for huffyuv)* - encoding: Set by user.* - decoding: unused*/int prediction_method;
#define FF_PRED_LEFT 0
#define FF_PRED_PLANE 1
#define FF_PRED_MEDIAN 2/*** slice offsets in the frame in bytes* - encoding: Set/allocated by libavcodec.* - decoding: Set/allocated by user (or NULL).*/int *slice_offset;/*** sample aspect ratio (0 if unknown)* That is the width of a pixel divided by the height of the pixel.* Numerator and denominator must be relatively prime and smaller than 256 for some video standards.* - encoding: Set by user.* - decoding: Set by libavcodec.*/AVRational sample_aspect_ratio;/*** motion estimation comparison function* - encoding: Set by user.* - decoding: unused*/int me_cmp;/*** subpixel motion estimation comparison function* - encoding: Set by user.* - decoding: unused*/int me_sub_cmp;/*** macroblock comparison function (not supported yet)* - encoding: Set by user.* - decoding: unused*/int mb_cmp;/*** interlaced DCT comparison function* - encoding: Set by user.* - decoding: unused*/int ildct_cmp;
#define FF_CMP_SAD 0
#define FF_CMP_SSE 1
#define FF_CMP_SATD 2
#define FF_CMP_DCT 3
#define FF_CMP_PSNR 4
#define FF_CMP_BIT 5
#define FF_CMP_RD 6
#define FF_CMP_ZERO 7
#define FF_CMP_VSAD 8
#define FF_CMP_VSSE 9
#define FF_CMP_NSSE 10
#define FF_CMP_W53 11
#define FF_CMP_W97 12
#define FF_CMP_DCTMAX 13
#define FF_CMP_DCT264 14
#define FF_CMP_CHROMA 256/*** ME diamond size & shape* - encoding: Set by user.* - decoding: unused*/int dia_size;/*** amount of previous MV predictors (2a+1 x 2a+1 square)* - encoding: Set by user.* - decoding: unused*/int last_predictor_count;/*** prepass for motion estimation* - encoding: Set by user.* - decoding: unused*/int pre_me;/*** motion estimation prepass comparison function* - encoding: Set by user.* - decoding: unused*/int me_pre_cmp;/*** ME prepass diamond size & shape* - encoding: Set by user.* - decoding: unused*/int pre_dia_size;/*** subpel ME quality* - encoding: Set by user.* - decoding: unused*/int me_subpel_quality;/*** DTG active format information (additional aspect ratio* information only used in DVB MPEG-2 transport streams)* 0 if not set.** - encoding: unused* - decoding: Set by decoder.*/int dtg_active_format;
#define FF_DTG_AFD_SAME 8
#define FF_DTG_AFD_4_3 9
#define FF_DTG_AFD_16_9 10
#define FF_DTG_AFD_14_9 11
#define FF_DTG_AFD_4_3_SP_14_9 13
#define FF_DTG_AFD_16_9_SP_14_9 14
#define FF_DTG_AFD_SP_4_3 15/*** maximum motion estimation search range in subpel units* If 0 then no limit.** - encoding: Set by user.* - decoding: unused*/int me_range;/*** intra quantizer bias* - encoding: Set by user.* - decoding: unused*/int intra_quant_bias;
#define FF_DEFAULT_QUANT_BIAS 999999/*** inter quantizer bias* - encoding: Set by user.* - decoding: unused*/int inter_quant_bias;#if FF_API_COLOR_TABLE_ID/*** color table ID* - encoding: unused* - decoding: Which clrtable should be used for 8bit RGB images.* Tables have to be stored somewhere. FIXME*/attribute_deprecated int color_table_id;
#endif/*** slice flags* - encoding: unused* - decoding: Set by user.*/int slice_flags;
#define SLICE_FLAG_CODED_ORDER 0x0001 ///< draw_horiz_band() is called in coded order instead of display
#define SLICE_FLAG_ALLOW_FIELD 0x0002 ///< allow draw_horiz_band() with field slices (MPEG2 field pics)
#define SLICE_FLAG_ALLOW_PLANE 0x0004 ///< allow draw_horiz_band() with 1 component at a time (SVQ1)/*** XVideo Motion Acceleration* - encoding: forbidden* - decoding: set by decoder*/int xvmc_acceleration;/*** macroblock decision mode* - encoding: Set by user.* - decoding: unused*/int mb_decision;
#define FF_MB_DECISION_SIMPLE 0 ///< uses mb_cmp
#define FF_MB_DECISION_BITS 1 ///< chooses the one which needs the fewest bits
#define FF_MB_DECISION_RD 2 ///< rate distortion/*** custom intra quantization matrix* - encoding: Set by user, can be NULL.* - decoding: Set by libavcodec.*/uint16_t *intra_matrix;/*** custom inter quantization matrix* - encoding: Set by user, can be NULL.* - decoding: Set by libavcodec.*/uint16_t *inter_matrix;/*** scene change detection threshold* 0 is default, larger means fewer detected scene changes.* - encoding: Set by user.* - decoding: unused*/int scenechange_threshold;/*** noise reduction strength* - encoding: Set by user.* - decoding: unused*/int noise_reduction;#if FF_API_INTER_THRESHOLD/*** @deprecated this field is unused*/attribute_deprecated int inter_threshold;
#endif#if FF_API_MPV_GLOBAL_OPTS/*** @deprecated use mpegvideo private options instead*/attribute_deprecated int quantizer_noise_shaping;
#endif/*** Motion estimation threshold below which no motion estimation is* performed, but instead the user specified motion vectors are used.** - encoding: Set by user.* - decoding: unused*/int me_threshold;/*** Macroblock threshold below which the user specified macroblock types will be used.* - encoding: Set by user.* - decoding: unused*/int mb_threshold;/*** precision of the intra DC coefficient - 8* - encoding: Set by user.* - decoding: unused*/int intra_dc_precision;/*** Number of macroblock rows at the top which are skipped.* - encoding: unused* - decoding: Set by user.*/int skip_top;/*** Number of macroblock rows at the bottom which are skipped.* - encoding: unused* - decoding: Set by user.*/int skip_bottom;/*** Border processing masking, raises the quantizer for mbs on the borders* of the picture.* - encoding: Set by user.* - decoding: unused*/float border_masking;/*** minimum MB lagrange multipler* - encoding: Set by user.* - decoding: unused*/int mb_lmin;/*** maximum MB lagrange multipler* - encoding: Set by user.* - decoding: unused*/int mb_lmax;/**** - encoding: Set by user.* - decoding: unused*/int me_penalty_compensation;/**** - encoding: Set by user.* - decoding: unused*/int bidir_refine;/**** - encoding: Set by user.* - decoding: unused*/int brd_scale;/*** minimum GOP size* - encoding: Set by user.* - decoding: unused*/int keyint_min;/*** number of reference frames* - encoding: Set by user.* - decoding: Set by lavc.*/int refs;/*** chroma qp offset from luma* - encoding: Set by user.* - decoding: unused*/int chromaoffset;/*** Multiplied by qscale for each frame and added to scene_change_score.* - encoding: Set by user.* - decoding: unused*/int scenechange_factor;/**** Note: Value depends upon the compare function used for fullpel ME.* - encoding: Set by user.* - decoding: unused*/int mv0_threshold;/*** Adjust sensitivity of b_frame_strategy 1.* - encoding: Set by user.* - decoding: unused*/int b_sensitivity;/*** Chromaticity coordinates of the source primaries.* - encoding: Set by user* - decoding: Set by libavcodec*/enum AVColorPrimaries color_primaries;/*** Color Transfer Characteristic.* - encoding: Set by user* - decoding: Set by libavcodec*/enum AVColorTransferCharacteristic color_trc;/*** YUV colorspace type.* - encoding: Set by user* - decoding: Set by libavcodec*/enum AVColorSpace colorspace;/*** MPEG vs JPEG YUV range.* - encoding: Set by user* - decoding: Set by libavcodec*/enum AVColorRange color_range;/*** This defines the location of chroma samples.* - encoding: Set by user* - decoding: Set by libavcodec*/enum AVChromaLocation chroma_sample_location;/*** Number of slices.* Indicates number of picture subdivisions. Used for parallelized* decoding.* - encoding: Set by user* - decoding: unused*/int slices;/** Field order* - encoding: set by libavcodec* - decoding: Set by user.*/enum AVFieldOrder field_order;/* audio only */int sample_rate; ///< samples per secondint channels; ///< number of audio channels/*** audio sample format* - encoding: Set by user.* - decoding: Set by libavcodec.*/enum AVSampleFormat sample_fmt; ///< sample format/* The following data should not be initialized. *//*** Samples per packet, initialized when calling 'init'.*/int frame_size;/*** Frame counter, set by libavcodec.** - decoding: total number of frames returned from the decoder so far.* - encoding: total number of frames passed to the encoder so far.** @note the counter is not incremented if encoding/decoding resulted in* an error.*/int frame_number;/*** number of bytes per packet if constant and known or 0* Used by some WAV based audio codecs.*/int block_align;/*** Audio cutoff bandwidth (0 means "automatic")* - encoding: Set by user.* - decoding: unused*/int cutoff;#if FF_API_REQUEST_CHANNELS/*** Decoder should decode to this many channels if it can (0 for default)* - encoding: unused* - decoding: Set by user.* @deprecated Deprecated in favor of request_channel_layout.*/int request_channels;
#endif/*** Audio channel layout.* - encoding: set by user.* - decoding: set by user, may be overwritten by libavcodec.*/uint64_t channel_layout;/*** Request decoder to use this channel layout if it can (0 for default)* - encoding: unused* - decoding: Set by user.*/uint64_t request_channel_layout;/*** Type of service that the audio stream conveys.* - encoding: Set by user.* - decoding: Set by libavcodec.*/enum AVAudioServiceType audio_service_type;/*** desired sample format* - encoding: Not used.* - decoding: Set by user.* Decoder will decode to this format if it can.*/enum AVSampleFormat request_sample_fmt;/*** Called at the beginning of each frame to get a buffer for it.** The function will set AVFrame.data[], AVFrame.linesize[].* AVFrame.extended_data[] must also be set, but it should be the same as* AVFrame.data[] except for planar audio with more channels than can fit* in AVFrame.data[]. In that case, AVFrame.data[] shall still contain as* many data pointers as it can hold.** if CODEC_CAP_DR1 is not set then get_buffer() must call* avcodec_default_get_buffer() instead of providing buffers allocated by* some other means.** AVFrame.data[] should be 32- or 16-byte-aligned unless the CPU doesn't* need it. avcodec_default_get_buffer() aligns the output buffer properly,* but if get_buffer() is overridden then alignment considerations should* be taken into account.** @see avcodec_default_get_buffer()** Video:** If pic.reference is set then the frame will be read later by libavcodec.* avcodec_align_dimensions2() should be used to find the required width and* height, as they normally need to be rounded up to the next multiple of 16.** If frame multithreading is used and thread_safe_callbacks is set,* it may be called from a different thread, but not from more than one at* once. Does not need to be reentrant.** @see release_buffer(), reget_buffer()* @see avcodec_align_dimensions2()** Audio:** Decoders request a buffer of a particular size by setting* AVFrame.nb_samples prior to calling get_buffer(). The decoder may,* however, utilize only part of the buffer by setting AVFrame.nb_samples* to a smaller value in the output frame.** Decoders cannot use the buffer after returning from* avcodec_decode_audio4(), so they will not call release_buffer(), as it* is assumed to be released immediately upon return.** As a convenience, av_samples_get_buffer_size() and* av_samples_fill_arrays() in libavutil may be used by custom get_buffer()* functions to find the required data size and to fill data pointers and* linesize. In AVFrame.linesize, only linesize[0] may be set for audio* since all planes must be the same size.** @see av_samples_get_buffer_size(), av_samples_fill_arrays()** - encoding: unused* - decoding: Set by libavcodec, user can override.*/int (*get_buffer)(struct AVCodecContext *c, AVFrame *pic);/*** Called to release buffers which were allocated with get_buffer.* A released buffer can be reused in get_buffer().* pic.data[*] must be set to NULL.* May be called from a different thread if frame multithreading is used,* but not by more than one thread at once, so does not need to be reentrant.* - encoding: unused* - decoding: Set by libavcodec, user can override.*/void (*release_buffer)(struct AVCodecContext *c, AVFrame *pic);/*** Called at the beginning of a frame to get cr buffer for it.* Buffer type (size, hints) must be the same. libavcodec won't check it.* libavcodec will pass previous buffer in pic, function should return* same buffer or new buffer with old frame "painted" into it.* If pic.data[0] == NULL must behave like get_buffer().* if CODEC_CAP_DR1 is not set then reget_buffer() must call* avcodec_default_reget_buffer() instead of providing buffers allocated by* some other means.* - encoding: unused* - decoding: Set by libavcodec, user can override.*/int (*reget_buffer)(struct AVCodecContext *c, AVFrame *pic);/* - encoding parameters */float qcompress; ///< amount of qscale change between easy & hard scenes (0.0-1.0)float qblur; ///< amount of qscale smoothing over time (0.0-1.0)/*** minimum quantizer* - encoding: Set by user.* - decoding: unused*/int qmin;/*** maximum quantizer* - encoding: Set by user.* - decoding: unused*/int qmax;/*** maximum quantizer difference between frames* - encoding: Set by user.* - decoding: unused*/int max_qdiff;/*** ratecontrol qmin qmax limiting method* 0-> clipping, 1-> use a nice continuous function to limit qscale wthin qmin/qmax.* - encoding: Set by user.* - decoding: unused*/float rc_qsquish;float rc_qmod_amp;int rc_qmod_freq;/*** decoder bitstream buffer size* - encoding: Set by user.* - decoding: unused*/int rc_buffer_size;/*** ratecontrol override, see RcOverride* - encoding: Allocated/set/freed by user.* - decoding: unused*/int rc_override_count;RcOverride *rc_override;/*** rate control equation* - encoding: Set by user* - decoding: unused*/const char *rc_eq;/*** maximum bitrate* - encoding: Set by user.* - decoding: unused*/int rc_max_rate;/*** minimum bitrate* - encoding: Set by user.* - decoding: unused*/int rc_min_rate;float rc_buffer_aggressivity;/*** initial complexity for pass1 ratecontrol* - encoding: Set by user.* - decoding: unused*/float rc_initial_cplx;/*** Ratecontrol attempt to use, at maximum, <value> of what can be used without an underflow.* - encoding: Set by user.* - decoding: unused.*/float rc_max_available_vbv_use;/*** Ratecontrol attempt to use, at least, <value> times the amount needed to prevent a vbv overflow.* - encoding: Set by user.* - decoding: unused.*/float rc_min_vbv_overflow_use;/*** Number of bits which should be loaded into the rc buffer before decoding starts.* - encoding: Set by user.* - decoding: unused*/int rc_initial_buffer_occupancy;#define FF_CODER_TYPE_VLC 0
#define FF_CODER_TYPE_AC 1
#define FF_CODER_TYPE_RAW 2
#define FF_CODER_TYPE_RLE 3
#define FF_CODER_TYPE_DEFLATE 4/*** coder type* - encoding: Set by user.* - decoding: unused*/int coder_type;/*** context model* - encoding: Set by user.* - decoding: unused*/int context_model;/*** minimum Lagrange multipler* - encoding: Set by user.* - decoding: unused*/int lmin;/*** maximum Lagrange multipler* - encoding: Set by user.* - decoding: unused*/int lmax;/*** frame skip threshold* - encoding: Set by user.* - decoding: unused*/int frame_skip_threshold;/*** frame skip factor* - encoding: Set by user.* - decoding: unused*/int frame_skip_factor;/*** frame skip exponent* - encoding: Set by user.* - decoding: unused*/int frame_skip_exp;/*** frame skip comparison function* - encoding: Set by user.* - decoding: unused*/int frame_skip_cmp;/*** trellis RD quantization* - encoding: Set by user.* - decoding: unused*/int trellis;/*** - encoding: Set by user.* - decoding: unused*/int min_prediction_order;/*** - encoding: Set by user.* - decoding: unused*/int max_prediction_order;/*** GOP timecode frame start number* - encoding: Set by user, in non drop frame format* - decoding: Set by libavcodec (timecode in the 25 bits format, -1 if unset)*/int64_t timecode_frame_start;/* The RTP callback: This function is called *//* every time the encoder has a packet to send. *//* It depends on the encoder if the data starts *//* with a Start Code (it should). H.263 does. *//* mb_nb contains the number of macroblocks *//* encoded in the RTP payload. */void (*rtp_callback)(struct AVCodecContext *avctx, void *data, int size, int mb_nb);int rtp_payload_size; /* The size of the RTP payload: the coder will *//* do its best to deliver a chunk with size *//* below rtp_payload_size, the chunk will start *//* with a start code on some codecs like H.263. *//* This doesn't take account of any particular *//* headers inside the transmitted RTP payload. *//* statistics, used for 2-pass encoding */int mv_bits;int header_bits;int i_tex_bits;int p_tex_bits;int i_count;int p_count;int skip_count;int misc_bits;/*** number of bits used for the previously encoded frame* - encoding: Set by libavcodec.* - decoding: unused*/int frame_bits;/*** pass1 encoding statistics output buffer* - encoding: Set by libavcodec.* - decoding: unused*/char *stats_out;/*** pass2 encoding statistics input buffer* Concatenated stuff from stats_out of pass1 should be placed here.* - encoding: Allocated/set/freed by user.* - decoding: unused*/char *stats_in;/*** Work around bugs in encoders which sometimes cannot be detected automatically.* - encoding: Set by user* - decoding: Set by user*/int workaround_bugs;
#define FF_BUG_AUTODETECT 1 ///< autodetection
#define FF_BUG_OLD_MSMPEG4 2
#define FF_BUG_XVID_ILACE 4
#define FF_BUG_UMP4 8
#define FF_BUG_NO_PADDING 16
#define FF_BUG_AMV 32
#define FF_BUG_AC_VLC 0 ///< Will be removed, libavcodec can now handle these non-compliant files by default.
#define FF_BUG_QPEL_CHROMA 64
#define FF_BUG_STD_QPEL 128
#define FF_BUG_QPEL_CHROMA2 256
#define FF_BUG_DIRECT_BLOCKSIZE 512
#define FF_BUG_EDGE 1024
#define FF_BUG_HPEL_CHROMA 2048
#define FF_BUG_DC_CLIP 4096
#define FF_BUG_MS 8192 ///< Work around various bugs in Microsoft's broken decoders.
#define FF_BUG_TRUNCATED 16384/*** strictly follow the standard (MPEG4, ...).* - encoding: Set by user.* - decoding: Set by user.* Setting this to STRICT or higher means the encoder and decoder will* generally do stupid things, whereas setting it to unofficial or lower* will mean the encoder might produce output that is not supported by all* spec-compliant decoders. Decoders don't differentiate between normal,* unofficial and experimental (that is, they always try to decode things* when they can) unless they are explicitly asked to behave stupidly* (=strictly conform to the specs)*/int strict_std_compliance;
#define FF_COMPLIANCE_VERY_STRICT 2 ///< Strictly conform to an older more strict version of the spec or reference software.
#define FF_COMPLIANCE_STRICT 1 ///< Strictly conform to all the things in the spec no matter what consequences.
#define FF_COMPLIANCE_NORMAL 0
#define FF_COMPLIANCE_UNOFFICIAL -1 ///< Allow unofficial extensions
#define FF_COMPLIANCE_EXPERIMENTAL -2 ///< Allow nonstandardized experimental things./*** error concealment flags* - encoding: unused* - decoding: Set by user.*/int error_concealment;
#define FF_EC_GUESS_MVS 1
#define FF_EC_DEBLOCK 2/*** debug* - encoding: Set by user.* - decoding: Set by user.*/int debug;
#define FF_DEBUG_PICT_INFO 1
#define FF_DEBUG_RC 2
#define FF_DEBUG_BITSTREAM 4
#define FF_DEBUG_MB_TYPE 8
#define FF_DEBUG_QP 16
#define FF_DEBUG_MV 32
#define FF_DEBUG_DCT_COEFF 0x00000040
#define FF_DEBUG_SKIP 0x00000080
#define FF_DEBUG_STARTCODE 0x00000100
#define FF_DEBUG_PTS 0x00000200
#define FF_DEBUG_ER 0x00000400
#define FF_DEBUG_MMCO 0x00000800
#define FF_DEBUG_BUGS 0x00001000
#define FF_DEBUG_VIS_QP 0x00002000
#define FF_DEBUG_VIS_MB_TYPE 0x00004000
#define FF_DEBUG_BUFFERS 0x00008000
#define FF_DEBUG_THREADS 0x00010000/*** debug* - encoding: Set by user.* - decoding: Set by user.*/int debug_mv;
#define FF_DEBUG_VIS_MV_P_FOR 0x00000001 //visualize forward predicted MVs of P frames
#define FF_DEBUG_VIS_MV_B_FOR 0x00000002 //visualize forward predicted MVs of B frames
#define FF_DEBUG_VIS_MV_B_BACK 0x00000004 //visualize backward predicted MVs of B frames/*** Error recognition; may misdetect some more or less valid parts as errors.* - encoding: unused* - decoding: Set by user.*/int err_recognition;
#define AV_EF_CRCCHECK (1<<0)
#define AV_EF_BITSTREAM (1<<1)
#define AV_EF_BUFFER (1<<2)
#define AV_EF_EXPLODE (1<<3)#define AV_EF_CAREFUL (1<<16)
#define AV_EF_COMPLIANT (1<<17)
#define AV_EF_AGGRESSIVE (1<<18)/*** opaque 64bit number (generally a PTS) that will be reordered and* output in AVFrame.reordered_opaque* @deprecated in favor of pkt_pts* - encoding: unused* - decoding: Set by user.*/int64_t reordered_opaque;/*** Hardware accelerator in use* - encoding: unused.* - decoding: Set by libavcodec*/struct AVHWAccel *hwaccel;/*** Hardware accelerator context.* For some hardware accelerators, a global context needs to be* provided by the user. In that case, this holds display-dependent* data FFmpeg cannot instantiate itself. Please refer to the* FFmpeg HW accelerator documentation to know how to fill this* is. e.g. for VA API, this is a struct vaapi_context.* - encoding: unused* - decoding: Set by user*/void *hwaccel_context;/*** error* - encoding: Set by libavcodec if flags&CODEC_FLAG_PSNR.* - decoding: unused*/uint64_t error[AV_NUM_DATA_POINTERS];/*** DCT algorithm, see FF_DCT_* below* - encoding: Set by user.* - decoding: unused*/int dct_algo;
#define FF_DCT_AUTO 0
#define FF_DCT_FASTINT 1
#define FF_DCT_INT 2
#define FF_DCT_MMX 3
#define FF_DCT_ALTIVEC 5
#define FF_DCT_FAAN 6/*** IDCT algorithm, see FF_IDCT_* below.* - encoding: Set by user.* - decoding: Set by user.*/int idct_algo;
#define FF_IDCT_AUTO 0
#define FF_IDCT_INT 1
#define FF_IDCT_SIMPLE 2
#define FF_IDCT_SIMPLEMMX 3
#define FF_IDCT_LIBMPEG2MMX 4
#define FF_IDCT_MMI 5
#define FF_IDCT_ARM 7
#define FF_IDCT_ALTIVEC 8
#define FF_IDCT_SH4 9
#define FF_IDCT_SIMPLEARM 10
#define FF_IDCT_H264 11
#define FF_IDCT_VP3 12
#define FF_IDCT_IPP 13
#define FF_IDCT_XVIDMMX 14
#define FF_IDCT_CAVS 15
#define FF_IDCT_SIMPLEARMV5TE 16
#define FF_IDCT_SIMPLEARMV6 17
#define FF_IDCT_SIMPLEVIS 18
#define FF_IDCT_WMV2 19
#define FF_IDCT_FAAN 20
#define FF_IDCT_EA 21
#define FF_IDCT_SIMPLENEON 22
#define FF_IDCT_SIMPLEALPHA 23
#define FF_IDCT_BINK 24#if FF_API_DSP_MASK/*** Unused.* @deprecated use av_set_cpu_flags_mask() instead.*/attribute_deprecated unsigned dsp_mask;
#endif/*** bits per sample/pixel from the demuxer (needed for huffyuv).* - encoding: Set by libavcodec.* - decoding: Set by user.*/int bits_per_coded_sample;/*** Bits per sample/pixel of internal libavcodec pixel/sample format.* - encoding: set by user.* - decoding: set by libavcodec.*/int bits_per_raw_sample;/*** low resolution decoding, 1-> 1/2 size, 2->1/4 size* - encoding: unused* - decoding: Set by user.*/int lowres;/*** the picture in the bitstream* - encoding: Set by libavcodec.* - decoding: Set by libavcodec.*/AVFrame *coded_frame;/*** thread count* is used to decide how many independent tasks should be passed to execute()* - encoding: Set by user.* - decoding: Set by user.*/int thread_count;/*** Which multithreading methods to use.* Use of FF_THREAD_FRAME will increase decoding delay by one frame per thread,* so clients which cannot provide future frames should not use it.** - encoding: Set by user, otherwise the default is used.* - decoding: Set by user, otherwise the default is used.*/int thread_type;
#define FF_THREAD_FRAME 1 ///< Decode more than one frame at once
#define FF_THREAD_SLICE 2 ///< Decode more than one part of a single frame at once/*** Which multithreading methods are in use by the codec.* - encoding: Set by libavcodec.* - decoding: Set by libavcodec.*/int active_thread_type;/*** Set by the client if its custom get_buffer() callback can be called* synchronously from another thread, which allows faster multithreaded decoding.* draw_horiz_band() will be called from other threads regardless of this setting.* Ignored if the default get_buffer() is used.* - encoding: Set by user.* - decoding: Set by user.*/int thread_safe_callbacks;/*** The codec may call this to execute several independent things.* It will return only after finishing all tasks.* The user may replace this with some multithreaded implementation,* the default implementation will execute the parts serially.* @param count the number of things to execute* - encoding: Set by libavcodec, user can override.* - decoding: Set by libavcodec, user can override.*/int (*execute)(struct AVCodecContext *c, int (*func)(struct AVCodecContext *c2, void *arg), void *arg2, int *ret, int count, int size);/*** The codec may call this to execute several independent things.* It will return only after finishing all tasks.* The user may replace this with some multithreaded implementation,* the default implementation will execute the parts serially.* Also see avcodec_thread_init and e.g. the --enable-pthread configure option.* @param c context passed also to func* @param count the number of things to execute* @param arg2 argument passed unchanged to func* @param ret return values of executed functions, must have space for "count" values. May be NULL.* @param func function that will be called count times, with jobnr from 0 to count-1.* threadnr will be in the range 0 to c->thread_count-1 < MAX_THREADS and so that no* two instances of func executing at the same time will have the same threadnr.* @return always 0 currently, but code should handle a future improvement where when any call to func* returns < 0 no further calls to func may be done and < 0 is returned.* - encoding: Set by libavcodec, user can override.* - decoding: Set by libavcodec, user can override.*/int (*execute2)(struct AVCodecContext *c, int (*func)(struct AVCodecContext *c2, void *arg, int jobnr, int threadnr), void *arg2, int *ret, int count);/*** thread opaque* Can be used by execute() to store some per AVCodecContext stuff.* - encoding: set by execute()* - decoding: set by execute()*/void *thread_opaque;/*** noise vs. sse weight for the nsse comparsion function* - encoding: Set by user.* - decoding: unused*/int nsse_weight;/*** profile* - encoding: Set by user.* - decoding: Set by libavcodec.*/int profile;
#define FF_PROFILE_UNKNOWN -99
#define FF_PROFILE_RESERVED -100#define FF_PROFILE_AAC_MAIN 0
#define FF_PROFILE_AAC_LOW 1
#define FF_PROFILE_AAC_SSR 2
#define FF_PROFILE_AAC_LTP 3
#define FF_PROFILE_AAC_HE 4
#define FF_PROFILE_AAC_HE_V2 28
#define FF_PROFILE_AAC_LD 22
#define FF_PROFILE_AAC_ELD 38#define FF_PROFILE_DTS 20
#define FF_PROFILE_DTS_ES 30
#define FF_PROFILE_DTS_96_24 40
#define FF_PROFILE_DTS_HD_HRA 50
#define FF_PROFILE_DTS_HD_MA 60#define FF_PROFILE_MPEG2_422 0
#define FF_PROFILE_MPEG2_HIGH 1
#define FF_PROFILE_MPEG2_SS 2
#define FF_PROFILE_MPEG2_SNR_SCALABLE 3
#define FF_PROFILE_MPEG2_MAIN 4
#define FF_PROFILE_MPEG2_SIMPLE 5#define FF_PROFILE_H264_CONSTRAINED (1<<9) // 8+1; constraint_set1_flag
#define FF_PROFILE_H264_INTRA (1<<11) // 8+3; constraint_set3_flag#define FF_PROFILE_H264_BASELINE 66
#define FF_PROFILE_H264_CONSTRAINED_BASELINE (66|FF_PROFILE_H264_CONSTRAINED)
#define FF_PROFILE_H264_MAIN 77
#define FF_PROFILE_H264_EXTENDED 88
#define FF_PROFILE_H264_HIGH 100
#define FF_PROFILE_H264_HIGH_10 110
#define FF_PROFILE_H264_HIGH_10_INTRA (110|FF_PROFILE_H264_INTRA)
#define FF_PROFILE_H264_HIGH_422 122
#define FF_PROFILE_H264_HIGH_422_INTRA (122|FF_PROFILE_H264_INTRA)
#define FF_PROFILE_H264_HIGH_444 144
#define FF_PROFILE_H264_HIGH_444_PREDICTIVE 244
#define FF_PROFILE_H264_HIGH_444_INTRA (244|FF_PROFILE_H264_INTRA)
#define FF_PROFILE_H264_CAVLC_444 44#define FF_PROFILE_VC1_SIMPLE 0
#define FF_PROFILE_VC1_MAIN 1
#define FF_PROFILE_VC1_COMPLEX 2
#define FF_PROFILE_VC1_ADVANCED 3#define FF_PROFILE_MPEG4_SIMPLE 0
#define FF_PROFILE_MPEG4_SIMPLE_SCALABLE 1
#define FF_PROFILE_MPEG4_CORE 2
#define FF_PROFILE_MPEG4_MAIN 3
#define FF_PROFILE_MPEG4_N_BIT 4
#define FF_PROFILE_MPEG4_SCALABLE_TEXTURE 5
#define FF_PROFILE_MPEG4_SIMPLE_FACE_ANIMATION 6
#define FF_PROFILE_MPEG4_BASIC_ANIMATED_TEXTURE 7
#define FF_PROFILE_MPEG4_HYBRID 8
#define FF_PROFILE_MPEG4_ADVANCED_REAL_TIME 9
#define FF_PROFILE_MPEG4_CORE_SCALABLE 10
#define FF_PROFILE_MPEG4_ADVANCED_CODING 11
#define FF_PROFILE_MPEG4_ADVANCED_CORE 12
#define FF_PROFILE_MPEG4_ADVANCED_SCALABLE_TEXTURE 13
#define FF_PROFILE_MPEG4_SIMPLE_STUDIO 14
#define FF_PROFILE_MPEG4_ADVANCED_SIMPLE 15/*** level* - encoding: Set by user.* - decoding: Set by libavcodec.*/int level;
#define FF_LEVEL_UNKNOWN -99/**** - encoding: unused* - decoding: Set by user.*/enum AVDiscard skip_loop_filter;/**** - encoding: unused* - decoding: Set by user.*/enum AVDiscard skip_idct;/**** - encoding: unused* - decoding: Set by user.*/enum AVDiscard skip_frame;/*** Header containing style information for text subtitles.* For SUBTITLE_ASS subtitle type, it should contain the whole ASS* [Script Info] and [V4+ Styles] section, plus the [Events] line and* the Format line following. It shouldn't include any Dialogue line.* - encoding: Set/allocated/freed by user (before avcodec_open2())* - decoding: Set/allocated/freed by libavcodec (by avcodec_open2())*/uint8_t *subtitle_header;int subtitle_header_size;/*** Simulates errors in the bitstream to test error concealment.* - encoding: Set by user.* - decoding: unused*/int error_rate;/*** Current packet as passed into the decoder, to avoid having* to pass the packet into every function. Currently only valid* inside lavc and get/release_buffer callbacks.* - decoding: set by avcodec_decode_*, read by get_buffer() for setting pkt_pts* - encoding: unused*/AVPacket *pkt;/*** VBV delay coded in the last frame (in periods of a 27 MHz clock).* Used for compliant TS muxing.* - encoding: Set by libavcodec.* - decoding: unused.*/uint64_t vbv_delay;/*** Timebase in which pkt_dts/pts and AVPacket.dts/pts are.* Code outside libavcodec should access this field using:* avcodec_set_pkt_timebase(avctx)* - encoding unused.* - decodimg set by user*/AVRational pkt_timebase;/*** AVCodecDescriptor* Code outside libavcodec should access this field using:* avcodec_get_codec_descriptior(avctx)* - encoding: unused.* - decoding: set by libavcodec.*/const AVCodecDescriptor *codec_descriptor;/*** Current statistics for PTS correction.* - decoding: maintained and used by libavcodec, not intended to be used by user apps* - encoding: unused*/int64_t pts_correction_num_faulty_pts; /// Number of incorrect PTS values so farint64_t pts_correction_num_faulty_dts; /// Number of incorrect DTS values so farint64_t pts_correction_last_pts; /// PTS of the last frameint64_t pts_correction_last_dts; /// DTS of the last frame
} AVCodecContext;光定义就真是够多的。下面挑一些关键的变量来看看（这里只考虑解码）。
enum AVMediaType codec_type：编解码器的类型（视频，音频...）
struct AVCodec *codec：采用的解码器AVCodec（H.264,MPEG2...）
int bit_rate：平均比特率
uint8_t *extradata; int extradata_size：针对特定编码器包含的附加信息（例如对于H.264解码器来说，存储SPS，PPS等）
AVRational time_base：根据该参数，可以把PTS转化为实际的时间（单位为秒s）
int width, height：如果是视频的话，代表宽和高
int refs：运动估计参考帧的个数（H.264的话会有多帧，MPEG2这类的一般就没有了）
int sample_rate：采样率（音频）
int channels：声道数（音频）
enum AVSampleFormat sample_fmt：采样格式
int profile：型（H.264里面就有，其他编码标准应该也有）
int level：级（和profile差不太多）
在这里需要注意：AVCodecContext中很多的参数是编码的时候使用的，而不是解码的时候使用的。
其实这些参数都比较容易理解。就不多费篇幅了。在这里看一下以下几个参数：
1.codec_type
编解码器类型有以下几种：
enum AVMediaType {AVMEDIA_TYPE_UNKNOWN = -1, ///< Usually treated as AVMEDIA_TYPE_DATAAVMEDIA_TYPE_VIDEO,AVMEDIA_TYPE_AUDIO,AVMEDIA_TYPE_DATA, ///< Opaque data information usually continuousAVMEDIA_TYPE_SUBTITLE,AVMEDIA_TYPE_ATTACHMENT, ///< Opaque data information usually sparseAVMEDIA_TYPE_NB
};2.sample_fmt
在FFMPEG中音频采样格式有以下几种：
enum AVSampleFormat {AV_SAMPLE_FMT_NONE = -1,AV_SAMPLE_FMT_U8, ///< unsigned 8 bitsAV_SAMPLE_FMT_S16, ///< signed 16 bitsAV_SAMPLE_FMT_S32, ///< signed 32 bitsAV_SAMPLE_FMT_FLT, ///< floatAV_SAMPLE_FMT_DBL, ///< doubleAV_SAMPLE_FMT_U8P, ///< unsigned 8 bits, planarAV_SAMPLE_FMT_S16P, ///< signed 16 bits, planarAV_SAMPLE_FMT_S32P, ///< signed 32 bits, planarAV_SAMPLE_FMT_FLTP, ///< float, planarAV_SAMPLE_FMT_DBLP, ///< double, planarAV_SAMPLE_FMT_NB ///< Number of sample formats. DO NOT USE if linking dynamically
};3.profile
在FFMPEG中型有以下几种，可以看出AAC，MPEG2，H.264，VC-1，MPEG4都有型的概念。
#define FF_PROFILE_UNKNOWN -99
#define FF_PROFILE_RESERVED -100#define FF_PROFILE_AAC_MAIN 0
#define FF_PROFILE_AAC_LOW 1
#define FF_PROFILE_AAC_SSR 2
#define FF_PROFILE_AAC_LTP 3
#define FF_PROFILE_AAC_HE 4
#define FF_PROFILE_AAC_HE_V2 28
#define FF_PROFILE_AAC_LD 22
#define FF_PROFILE_AAC_ELD 38#define FF_PROFILE_DTS 20
#define FF_PROFILE_DTS_ES 30
#define FF_PROFILE_DTS_96_24 40
#define FF_PROFILE_DTS_HD_HRA 50
#define FF_PROFILE_DTS_HD_MA 60#define FF_PROFILE_MPEG2_422 0
#define FF_PROFILE_MPEG2_HIGH 1
#define FF_PROFILE_MPEG2_SS 2
#define FF_PROFILE_MPEG2_SNR_SCALABLE 3
#define FF_PROFILE_MPEG2_MAIN 4
#define FF_PROFILE_MPEG2_SIMPLE 5#define FF_PROFILE_H264_CONSTRAINED (1<<9) // 8+1; constraint_set1_flag
#define FF_PROFILE_H264_INTRA (1<<11) // 8+3; constraint_set3_flag#define FF_PROFILE_H264_BASELINE 66
#define FF_PROFILE_H264_CONSTRAINED_BASELINE (66|FF_PROFILE_H264_CONSTRAINED)
#define FF_PROFILE_H264_MAIN 77
#define FF_PROFILE_H264_EXTENDED 88
#define FF_PROFILE_H264_HIGH 100
#define FF_PROFILE_H264_HIGH_10 110
#define FF_PROFILE_H264_HIGH_10_INTRA (110|FF_PROFILE_H264_INTRA)
#define FF_PROFILE_H264_HIGH_422 122
#define FF_PROFILE_H264_HIGH_422_INTRA (122|FF_PROFILE_H264_INTRA)
#define FF_PROFILE_H264_HIGH_444 144
#define FF_PROFILE_H264_HIGH_444_PREDICTIVE 244
#define FF_PROFILE_H264_HIGH_444_INTRA (244|FF_PROFILE_H264_INTRA)
#define FF_PROFILE_H264_CAVLC_444 44#define FF_PROFILE_VC1_SIMPLE 0
#define FF_PROFILE_VC1_MAIN 1
#define FF_PROFILE_VC1_COMPLEX 2
#define FF_PROFILE_VC1_ADVANCED 3#define FF_PROFILE_MPEG4_SIMPLE 0
#define FF_PROFILE_MPEG4_SIMPLE_SCALABLE 1
#define FF_PROFILE_MPEG4_CORE 2
#define FF_PROFILE_MPEG4_MAIN 3
#define FF_PROFILE_MPEG4_N_BIT 4
#define FF_PROFILE_MPEG4_SCALABLE_TEXTURE 5
#define FF_PROFILE_MPEG4_SIMPLE_FACE_ANIMATION 6
#define FF_PROFILE_MPEG4_BASIC_ANIMATED_TEXTURE 7
#define FF_PROFILE_MPEG4_HYBRID 8
#define FF_PROFILE_MPEG4_ADVANCED_REAL_TIME 9
#define FF_PROFILE_MPEG4_CORE_SCALABLE 10
#define FF_PROFILE_MPEG4_ADVANCED_CODING 11
#define FF_PROFILE_MPEG4_ADVANCED_CORE 12
#define FF_PROFILE_MPEG4_ADVANCED_SCALABLE_TEXTURE 13
#define FF_PROFILE_MPEG4_SIMPLE_STUDIO 14
#define FF_PROFILE_MPEG4_ADVANCED_SIMPLE 15FFMPEG结构体分析：AVCodecContext相关推荐
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