FFMPEG结构体分析：AVCodecContext(二)
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* 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 second
int 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;
/**
* ratecontro