FFMPeg代码分析：AVCodecContext结构体
2024-04-21 18:55:12
在调用avformat_open_input打开文件后，下一步调用av_find_stream_info函数从文件中读取音视频流的信息，而后AVFormatContext的结构体将会将这些信息保存在其中。在找到AVFormatContext的视频stream后，获取其codec保存到指向AVCodecContext的指针：
// Find the first video stream
for(i=0; i<pFormatCtx->nb_streams; i++)
{ if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO && videoStream<0){ videoStream=i; }
}
if(videoStream==-1) return -1; // Didn't find a video stream // Get a pointer to the codec context for the video stream pCodecCtx=pFormatCtx->streams[videoStream]->codec;
编解码器上下文AVCodecContext的定义如下：
typedef struct AVCodecContext {const AVClass *av_class;//当前结构体的“基类”int log_level_offset;enum AVMediaType codec_type; //媒体类型，主要有AVMEDIA_TYPE_VIDEO视频、AVMEDIA_TYPE_AUDIO音频、AVMEDIA_TYPE_SUBTITLE字幕等const struct AVCodec *codec;//编解码器结构体char codec_name[32];enum AVCodecID codec_id; //枚举变量，标识编解码器的id，例如AV_CODEC_ID_MPEG2VIDEO、AV_CODEC_ID_H264、AV_CODEC_ID_HEVC等unsigned int codec_tag;unsigned int stream_codec_tag;void *priv_data;struct AVCodecInternal *internal;void *opaque;int bit_rate;//平均码率，解码时由libavcodec设定int bit_rate_tolerance;int global_quality;int compression_level;
#define FF_COMPRESSION_DEFAULT -1int flags;int flags2;uint8_t *extradata;//保存编解码器的附加信息，如参数集合等int extradata_size;AVRational time_base;//用于时间转换的参数int ticks_per_frame;int delay;int width, height;//视频的分辨率int coded_width, coded_height;#define FF_ASPECT_EXTENDED 15int gop_size;//编码时图像组的长度；enum AVPixelFormat pix_fmt;//图像像素的格式，例如AV_PIX_FMT_YUV420P、AV_PIX_FMT_YUYV422、AV_PIX_FMT_RGB24等int me_method;//编码所采用的运动搜索算法void (*draw_horiz_band)(struct AVCodecContext *s, const AVFrame *src, int offset[AV_NUM_DATA_POINTERS],int y, int type, int height);enum AVPixelFormat (*get_format)(struct AVCodecContext *s, const enum AVPixelFormat * fmt);int max_b_frames;//最大b帧数float b_quant_factor;/** obsolete FIXME remove */int rc_strategy;
#define FF_RC_STRATEGY_XVID 1int b_frame_strategy;float b_quant_offset;int has_b_frames;int mpeg_quant;float i_quant_factor;float i_quant_offset;float lumi_masking;float temporal_cplx_masking;float spatial_cplx_masking;float p_masking;float dark_masking;int slice_count;//条带数目int prediction_method;
#define FF_PRED_LEFT 0
#define FF_PRED_PLANE 1
#define FF_PRED_MEDIAN 2int *slice_offset;AVRational sample_aspect_ratio;int me_cmp;int me_sub_cmp;int mb_cmp;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 256int dia_size;int last_predictor_count;int pre_me;int me_pre_cmp;int pre_dia_size;int me_subpel_quality;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 15int me_range;int intra_quant_bias;
#define FF_DEFAULT_QUANT_BIAS 999999int inter_quant_bias;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)int xvmc_acceleration;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;/*** 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. *//*** Number of samples per channel in an audio frame.** - encoding: set by libavcodec in avcodec_open2(). Each submitted frame* except the last must contain exactly frame_size samples per channel.* May be 0 when the codec has CODEC_CAP_VARIABLE_FRAME_SIZE set, then the* frame size is not restricted.* - decoding: may be set by some decoders to indicate constant frame size*/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.*/attribute_deprecated 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;#if FF_API_GET_BUFFER/*** 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. In some rare cases,* a decoder may need to call get_buffer() more than once in a single* call to avcodec_decode_audio4(). In that case, when get_buffer() is* called again after it has already been called once, the previously* acquired buffer is assumed to be released at that time and may not be* reused by the decoder.** 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.** @deprecated use get_buffer2()*/attribute_deprecatedint (*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.** @deprecated custom freeing callbacks should be set from get_buffer2()*/attribute_deprecatedvoid (*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.*/attribute_deprecatedint (*reget_buffer)(struct AVCodecContext *c, AVFrame *pic);
#endif/*** This callback is called at the beginning of each frame to get data* buffer(s) for it. There may be one contiguous buffer for all the data or* there may be a buffer per each data plane or anything in between. What* this means is, you may set however many entries in buf[] you feel necessary.* Each buffer must be reference-counted using the AVBuffer API (see description* of buf[] below).** The following fields will be set in the frame before this callback is* called:* - format* - width, height (video only)* - sample_rate, channel_layout, nb_samples (audio only)* Their values may differ from the corresponding values in* AVCodecContext. This callback must use the frame values, not the codec* context values, to calculate the required buffer size.** This callback must fill the following fields in the frame:* - data[]* - linesize[]* - extended_data:* * if the data is planar audio with more than 8 channels, then this* callback must allocate and fill extended_data to contain all pointers* to all data planes. data[] must hold as many pointers as it can.* extended_data must be allocated with av_malloc() and will be freed in* av_frame_unref().* * otherwise exended_data must point to data* - buf[] must contain one or more pointers to AVBufferRef structures. Each of* the frame's data and extended_data pointers must be contained in these. That* is, one AVBufferRef for each allocated chunk of memory, not necessarily one* AVBufferRef per data[] entry. See: av_buffer_create(), av_buffer_alloc(),* and av_buffer_ref().* - extended_buf and nb_extended_buf must be allocated with av_malloc() by* this callback and filled with the extra buffers if there are more* buffers than buf[] can hold. extended_buf will be freed in* av_frame_unref().** If CODEC_CAP_DR1 is not set then get_buffer2() must call* avcodec_default_get_buffer2() instead of providing buffers allocated by* some other means.** Each data plane must be aligned to the maximum required by the target* CPU.** @see avcodec_default_get_buffer2()** Video:** If AV_GET_BUFFER_FLAG_REF is set in flags then the frame may be reused* (read and/or written to if it is writable) later by libavcodec.** If CODEC_FLAG_EMU_EDGE is not set in s->flags, the buffer must contain an* edge of the size returned by avcodec_get_edge_width() on all sides.** 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,* this callback may be called from a different thread, but not from more* than one at once. Does not need to be reentrant.** @see avcodec_align_dimensions2()** Audio:** Decoders request a buffer of a particular size by setting* AVFrame.nb_samples prior to calling get_buffer2(). The decoder may,* however, utilize only part of the buffer by setting AVFrame.nb_samples* to a smaller value in the output frame.** As a convenience, av_samples_get_buffer_size() and* av_samples_fill_arrays() in libavutil may be used by custom get_buffer2()* 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_buffer2)(struct AVCodecContext *s, AVFrame *frame, int flags);/*** If non-zero, the decoded audio and video frames returned from* avcodec_decode_video2() and avcodec_decode_audio4() are reference-counted* and are valid indefinitely. The caller must free them with* av_frame_unref() when they are not needed anymore.* Otherwise, the decoded frames must not be freed by the caller and are* only valid until the next decode call.** - encoding: unused* - decoding: set by the caller before avcodec_open2().*/int refcounted_frames;/* - 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) ///< verify embedded CRCs
#define AV_EF_BITSTREAM (1<<1) ///< detect bitstream specification deviations
#define AV_EF_BUFFER (1<<2) ///< detect improper bitstream length
#define AV_EF_EXPLODE (1<<3) ///< abort decoding on minor error detection#define AV_EF_CAREFUL (1<<16) ///< consider things that violate the spec, are fast to calculate and have not been seen in the wild as errors
#define AV_EF_COMPLIANT (1<<17) ///< consider all spec non compliancies as errors
#define AV_EF_AGGRESSIVE (1<<18) ///< consider things that a sane encoder should not do as an error/*** 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_ARM 7
#define FF_IDCT_ALTIVEC 8
#define FF_IDCT_SH4 9
#define FF_IDCT_SIMPLEARM 10
#define FF_IDCT_IPP 13
#define FF_IDCT_XVIDMMX 14
#define FF_IDCT_SIMPLEARMV5TE 16
#define FF_IDCT_SIMPLEARMV6 17
#define FF_IDCT_SIMPLEVIS 18
#define FF_IDCT_FAAN 20
#define FF_IDCT_SIMPLENEON 22
#define FF_IDCT_SIMPLEALPHA 23/*** 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;#if FF_API_LOWRES/*** low resolution decoding, 1-> 1/2 size, 2->1/4 size* - encoding: unused* - decoding: Set by user.* Code outside libavcodec should access this field using:* av_codec_{get,set}_lowres(avctx)*/int lowres;
#endif/*** 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_MPEG2_AAC_LOW 128
#define FF_PROFILE_MPEG2_AAC_HE 131#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#define FF_PROFILE_JPEG2000_CSTREAM_RESTRICTION_0 0
#define FF_PROFILE_JPEG2000_CSTREAM_RESTRICTION_1 1
#define FF_PROFILE_JPEG2000_CSTREAM_NO_RESTRICTION 2
#define FF_PROFILE_JPEG2000_DCINEMA_2K 3
#define FF_PROFILE_JPEG2000_DCINEMA_4K 4/*** level* - encoding: Set by user.* - decoding: Set by libavcodec.*/int level;
#define FF_LEVEL_UNKNOWN -99/*** Skip loop filtering for selected frames.* - encoding: unused* - decoding: Set by user.*/enum AVDiscard skip_loop_filter;/*** Skip IDCT/dequantization for selected frames.* - encoding: unused* - decoding: Set by user.*/enum AVDiscard skip_idct;/*** Skip decoding for selected frames.* - 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:* av_codec_{get,set}_pkt_timebase(avctx)* - encoding unused.* - decoding set by user.*/AVRational pkt_timebase;/*** AVCodecDescriptor* Code outside libavcodec should access this field using:* av_codec_{get,set}_codec_descriptor(avctx)* - encoding: unused.* - decoding: set by libavcodec.*/const AVCodecDescriptor *codec_descriptor;#if !FF_API_LOWRES/*** low resolution decoding, 1-> 1/2 size, 2->1/4 size* - encoding: unused* - decoding: Set by user.* Code outside libavcodec should access this field using:* av_codec_{get,set}_lowres(avctx)*/int lowres;
#endif/*** 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/*** Character encoding of the input subtitles file.* - decoding: set by user* - encoding: unused*/char *sub_charenc;/*** Subtitles character encoding mode. Formats or codecs might be adjusting* this setting (if they are doing the conversion themselves for instance).* - decoding: set by libavcodec* - encoding: unused*/int sub_charenc_mode;
#define FF_SUB_CHARENC_MODE_DO_NOTHING -1 ///< do nothing (demuxer outputs a stream supposed to be already in UTF-8, or the codec is bitmap for instance)
#define FF_SUB_CHARENC_MODE_AUTOMATIC 0 ///< libavcodec will select the mode itself
#define FF_SUB_CHARENC_MODE_PRE_DECODER 1 ///< the AVPacket data needs to be recoded to UTF-8 before being fed to the decoder, requires iconv/*** Skip processing alpha if supported by codec.* Note that if the format uses pre-multiplied alpha (common with VP6,* and recommended due to better video quality/compression)* the image will look as if alpha-blended onto a black background.* However for formats that do not use pre-multiplied alpha* there might be serious artefacts (though e.g. libswscale currently* assumes pre-multiplied alpha anyway).* Code outside libavcodec should access this field using AVOptions** - decoding: set by user* - encoding: unused*/int skip_alpha;/*** Number of samples to skip after a discontinuity* - decoding: unused* - encoding: set by libavcodec*/int seek_preroll;
} AVCodecContext;这个结构体的内容极其庞大繁杂，但是看过其成员后便明白，它保存了编码视频时所用到的各种参数，包括编码格式即所用的编码器、编码过程中的参数等。其中很多都是编码标准算法中的相应的设置，比如GOP的大小，参考帧的数目，运动搜索范围的选择等等。具体技术细节比较复杂，需要学习的还要参考相应的编解码标准。
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