出自：http://blog.itpub.net/30168498/viewspace-1576794/
通过上一篇文章，我们用ffmpeg分离出一个多媒体容器中的音视频数据，但是很可能这些数据是不能被正确解码的。为什么呢？因为在解码这些数据之前，需要对解码器做一些配置，典型的就是目前流行的高清编码“黄金搭档”组合H264 + AAC的搭配。本文将讲述H264和AAC的关键解码配置参数的解析，如果没有这些配置信息，数据帧往往不完整，导致了解码器不能解码。
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H264的配置信息解析
前面我们知道，ffmpeg的avformat_find_stream_info函数可以取得音视频媒体多种，比如播放持续时间、音视频压缩格式、音轨信息、字幕信息、帧率、采样率等。在信息结果中有一项扩展数据描述（avcodec.h文件中）：
AVCodecContext定义如下：
/** * 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; #if FF_API_CODEC_NAME /** * @deprecated this field is not used for anything in libavcodec */ attribute_deprecated char codec_name[32]; #endif 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; #if FF_API_STREAM_CODEC_TAG /** * @deprecated this field is unused */ attribute_deprecated unsigned int stream_codec_tag; #endif void *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 problems 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. * This often, but not always is the inverse of the frame rate or field rate * for video. * - encoding: MUST be set by user. * - decoding: the use of this field for decoding is deprecated. * Use framerate instead. */ 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; /** * Codec delay. * * 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 field is unused (see initial_padding). * * 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: May be set by the user before opening the decoder if known e.g. * from the container. Some decoders will require the dimensions * to be set by the caller. During decoding, the decoder may * overwrite those values as required. */ int width, height; /** * Bitstream width / height, may be different from width/height e.g. when * the decoded frame is cropped before being output or lowres is enabled. * - encoding: unused * - decoding: May be set by the user before opening the decoder if known * e.g. from the container. During decoding, the decoder may * overwrite those values as required. */ int coded_width, coded_height; #if FF_API_ASPECT_EXTENDED #define FF_ASPECT_EXTENDED 15 #endif /** * 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. * @note The callback may be called again immediately if initialization for * the selected (hardware-accelerated) pixel format failed. * @warning Behavior is undefined if the callback returns a value not * in the fmt list of formats. * @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 1 int b_frame_strategy; /** * 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; #if FF_API_AFD /** * 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. * @deprecated Deprecated in favor of AVSideData */ attribute_deprecated 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 #endif /* FF_API_AFD */ /** * 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; /** * 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) #if FF_API_XVMC /** * XVideo Motion Acceleration * - encoding: forbidden * - decoding: set by decoder * @deprecated XvMC doesn't need it anymore. */ attribute_deprecated int xvmc_acceleration; #endif /* FF_API_XVMC */ /** * 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_MPV_OPT /** * @deprecated this field is unused */ attribute_deprecated int me_threshold; /** * @deprecated this field is unused */ attribute_deprecated int mb_threshold; #endif /** * precision of the intra DC coefficient - 8 * - encoding: Set by user. * - decoding: Set by libavcodec */ 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; #if FF_API_MPV_OPT /** * @deprecated use encoder private options instead */ attribute_deprecated float border_masking; #endif /** * 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; #if FF_API_UNUSED_MEMBERS /** * Multiplied by qscale for each frame and added to scene_change_score. * - encoding: Set by user. * - decoding: unused */ attribute_deprecated int scenechange_factor; #endif /** * * 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. */ /** * 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_deprecated 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. * * @deprecated custom freeing callbacks should be set from get_buffer2() */ attribute_deprecated 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. */ attribute_deprecated int (*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. * * 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. * * Some decoders do not support linesizes changing between frames. * * 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; #if FF_API_MPV_OPT /** * @deprecated use encoder private options instead */ attribute_deprecated float rc_qsquish; attribute_deprecated float rc_qmod_amp; attribute_deprecated int rc_qmod_freq; #endif /** * 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; #if FF_API_MPV_OPT /** * @deprecated use encoder private options instead */ attribute_deprecated const char *rc_eq; #endif /** * maximum bitrate * - encoding: Set by user. * - decoding: Set by libavcodec. */ int rc_max_rate; /** * minimum bitrate * - encoding: Set by user. * - decoding: unused */ int rc_min_rate; #if FF_API_MPV_OPT /** * @deprecated use encoder private options instead */ attribute_deprecated float rc_buffer_aggressivity; attribute_deprecated float rc_initial_cplx; #endif /** * 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 #if FF_API_UNUSED_MEMBERS #define FF_CODER_TYPE_DEFLATE 4 #endif /* FF_API_UNUSED_MEMBERS */ /** * coder type * - encoding: Set by user. * - decoding: unused */ int coder_type; /** * context model * - encoding: Set by user. * - decoding: unused */ int context_model; #if FF_API_MPV_OPT /** * @deprecated use encoder private options instead */ attribute_deprecated int lmin; /** * @deprecated use encoder private options instead */ attribute_deprecated int lmax; #endif /** * 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 #if FF_API_OLD_MSMPEG4 #define FF_BUG_OLD_MSMPEG4 2 #endif #define FF_BUG_XVID_ILACE 4 #define FF_BUG_UMP4 8 #define FF_BUG_NO_PADDING 16 #define FF_BUG_AMV 32 #if FF_API_AC_VLC #define FF_BUG_AC_VLC 0 ///< Will be removed, libavcodec can now handle these non-compliant files by default. #endif #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 #define FF_EC_FAVOR_INTER 256 /** * 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 #if FF_API_DEBUG_MV /** * @deprecated this option does nothing */ #define FF_DEBUG_MV 32 #endif #define FF_DEBUG_DCT_COEFF 0x00000040 #define FF_DEBUG_SKIP 0x00000080 #define FF_DEBUG_STARTCODE 0x00000100 #if FF_API_UNUSED_MEMBERS #define FF_DEBUG_PTS 0x00000200 #endif /* FF_API_UNUSED_MEMBERS */ #define FF_DEBUG_ER 0x00000400 #define FF_DEBUG_MMCO 0x00000800 #define FF_DEBUG_BUGS 0x00001000 #if FF_API_DEBUG_MV #define FF_DEBUG_VIS_QP 0x00002000 ///< only access through AVOptions from outside libavcodec #define FF_DEBUG_VIS_MB_TYPE 0x00004000 ///< only access through AVOptions from outside libavcodec #endif #define FF_DEBUG_BUFFERS 0x00008000 #define FF_DEBUG_THREADS 0x00010000 #define FF_DEBUG_NOMC 0x01000000 #if FF_API_DEBUG_MV /** * debug * Code outside libavcodec should access this field using AVOptions * - 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 #endif /** * Error recognition; may misdetect some more or less valid parts as errors. * - encoding: unused * - decoding: Set by user. */ int err_recognition; /** * Verify checksums embedded in the bitstream (could be of either encoded or * decoded data, depending on the codec) and print an error message on mismatch. * If AV_EF_EXPLODE is also set, a mismatching checksum will result in the * decoder returning an error. */ #define AV_EF_CRCCHECK (1<<0) #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_IGNORE_ERR (1<<15) ///< ignore errors and continue #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 compliances 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 * - 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 #if FF_API_UNUSED_MEMBERS #define FF_DCT_INT 2 #endif /* FF_API_UNUSED_MEMBERS */ #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 #if FF_API_ARCH_SH4 #define FF_IDCT_SH4 9 #endif #define FF_IDCT_SIMPLEARM 10 #if FF_API_UNUSED_MEMBERS #define FF_IDCT_IPP 13 #endif /* FF_API_UNUSED_MEMBERS */ #define FF_IDCT_XVID 14 #if FF_API_IDCT_XVIDMMX #define FF_IDCT_XVIDMMX 14 #endif /* FF_API_IDCT_XVIDMMX */ #define FF_IDCT_SIMPLEARMV5TE 16 #define FF_IDCT_SIMPLEARMV6 17 #if FF_API_ARCH_SPARC #define FF_IDCT_SIMPLEVIS 18 #endif #define FF_IDCT_FAAN 20 #define FF_IDCT_SIMPLENEON 22 #if FF_API_ARCH_ALPHA #define FF_IDCT_SIMPLEALPHA 23 #endif #define FF_IDCT_SIMPLEAUTO 128 /** * 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: unused */ 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); #if FF_API_THREAD_OPAQUE /** * @deprecated this field should not be used from outside of lavc */ attribute_deprecated void *thread_opaque; #endif /** * noise vs. sse weight for the nsse comparison 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_DTS_EXPRESS 70 #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 #define FF_PROFILE_HEVC_MAIN 1 #define FF_PROFILE_HEVC_MAIN_10 2 #define FF_PROFILE_HEVC_MAIN_STILL_PICTURE 3 #define FF_PROFILE_HEVC_REXT 4 #define FF_PROFILE_VP9_0 0 #define FF_PROFILE_VP9_1 1 #define FF_PROFILE_VP9_2 2 #define FF_PROFILE_VP9_3 3 /** * 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; #if FF_API_ERROR_RATE /** * @deprecated use the 'error_rate' private AVOption of the mpegvideo * encoders */ attribute_deprecated int error_rate; #endif #if FF_API_CODEC_PKT /** * @deprecated this field is not supposed to be accessed from outside lavc */ attribute_deprecated AVPacket *pkt; #endif /** * 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; /** * Encoding only. Allow encoders to output packets that do not contain any * encoded data, only side data. * * Some encoders need to output such packets, e.g. to update some stream * parameters at the end of encoding. * * All callers are strongly recommended to set this option to 1 and update * their code to deal with such packets, since this behaviour may become * always enabled in the future (then this option will be deprecated and * later removed). To avoid ABI issues when this happens, the callers should * use AVOptions to set this field. */ int side_data_only_packets; /** * Audio only. The number of "priming" samples (padding) inserted by the * encoder at the beginning of the audio. I.e. this number of leading * decoded samples must be discarded by the caller to get the original audio * without leading padding. * * - decoding: unused * - encoding: Set by libavcodec. The timestamps on the output packets are * adjusted by the encoder so that they always refer to the * first sample of the data actually contained in the packet, * including any added padding. E.g. if the timebase is * 1/samplerate and the timestamp of the first input sample is * 0, the timestamp of the first output packet will be * -initial_padding. */ int initial_padding; /** * - decoding: For codecs that store a framerate value in the compressed * bitstream, the decoder may export it here. { 0, 1} when * unknown. * - encoding: unused */ AVRational framerate; /** * Nominal unaccelerated pixel format, see AV_PIX_FMT_xxx. * - encoding: unused. * - decoding: Set by libavcodec before calling get_format() */ enum AVPixelFormat sw_pix_fmt; /** * 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 far int64_t pts_correction_num_faulty_dts; /// Number of incorrect DTS values so far int64_t pts_correction_last_pts; /// PTS of the last frame int64_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; #if !FF_API_DEBUG_MV /** * debug motion vectors * Code outside libavcodec should access this field using AVOptions * - 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 #endif /** * custom intra quantization matrix * Code outside libavcodec should access this field using av_codec_g/set_chroma_intra_matrix() * - encoding: Set by user, can be NULL. * - decoding: unused. */ uint16_t *chroma_intra_matrix; /** * dump format separator. * can be ", " or " " or anything else * Code outside libavcodec should access this field using AVOptions * (NO direct access). * - encoding: Set by user. * - decoding: Set by user. */ uint8_t *dump_separator; /** * ',' separated list of allowed decoders. * If NULL then all are allowed * - encoding: unused * - decoding: set by user through AVOPtions (NO direct access) */ char *codec_whitelist; } AVCodecContext;
如果视频流是H264，这个extradate里面就包含了H264的配置信息，这个扩展数据有如下定义：
详细解释可以参考“ISO-14496-15 AVC file format”文档。里面最重要的就是NAL长度和SPS，PPS数据和对应的长度信息。对该数据的解析在ffmpeg里面有现成的函数：ff_h264_decode_extradata，在我的项目里面是自己写的扩展数据解析。
-
AAC的配置信息解析及设置
如果音频数据是AAC流，在解码时需要ADTS(Audio Data Transport Stream)头部，不管是容器封装还是流媒体，没有这个，一般都是不能播放的。很多朋友在做AAC流播放时遇到播不出声音，很可能就是这个原因导致。
ADTS所需的数据仍然是放在上面的扩展数据extradata中，我们需要先解码这个扩展数据，然后再从解码后的数据信息里面重新封装成ADTS头信息，加到每一帧AAC数据之前再送解码器，这样就可以正常解码了。
extradate数据定义如下：
详细信息及说明请参考“ISO-IEC-14496-3 (Audio)”的AudioSpecificConfig部分。里面最重要的部分有采样频率、通道配置和音频对象类型，这几个一般都是AAC解码器需要的配置参数。
这个数据在ffmpeg中也有相应的解码函数：avpriv_aac_parse_header。在我的项目中，我没有使用这个函数，而是自己实现的
typedef struct { int write_adts; int objecttype; int sample_rate_index; int channel_conf; }ADTSContext;
int aac_decode_extradata(ADTSContext *adts, unsigned char *pbuf, int bufsize) { int aot, aotext, samfreindex; int i, channelconfig; unsigned char *p = pbuf; if (!adts || !pbuf || bufsize<2) { return -1; } aot = (p[0]>>3)&0x1f; if (aot == 31) { aotext = (p[0]<<3 | (p[1]>>5)) & 0x3f; aot = 32 + aotext; samfreindex = (p[1]>>1) & 0x0f; if (samfreindex == 0x0f) { channelconfig = ((p[4]<<3) | (p[5]>>5)) & 0x0f; } else { channelconfig = ((p[1]<<3)|(p[2]>>5)) & 0x0f; } } else { samfreindex = ((p[0]<<1)|p[1]>>7) & 0x0f; if (samfreindex == 0x0f) { channelconfig = (p[4]>>3) & 0x0f; } else { channelconfig = (p[1]>>3) & 0x0f; } } #ifdef AOT_PROFILE_CTRL if (aot < 2) aot = 2; #endif adts->objecttype = aot-1; adts->sample_rate_index = samfreindex; adts->channel_conf = channelconfig; adts->write_adts = 1; return 0; }
上面的pbuf就是extradata。
接下来，再用ADTSContext数据编码为ADTS头信息插入每一个AAC帧前面：
int aac_set_adts_head(ADTSContext *acfg, unsigned char *buf, int size) { unsigned char byte; if (size < ADTS_HEADER_SIZE) { return -1; } buf[0] = 0xff; buf[1] = 0xf1; byte = 0; byte |= (acfg->objecttype & 0x03) << 6; byte |= (acfg->sample_rate_index & 0x0f) << 2; byte |= (acfg->channel_conf & 0x07) >> 2; buf[2] = byte; byte = 0; byte |= (acfg->channel_conf & 0x07) << 6; byte |= (ADTS_HEADER_SIZE + size) >> 11; buf[3] = byte; byte = 0; byte |= (ADTS_HEADER_SIZE + size) >> 3; buf[4] = byte; byte = 0; byte |= ((ADTS_HEADER_SIZE + size) & 0x7) << 5; byte |= (0x7ff >> 6) & 0x1f; buf[5] = byte; byte = 0; byte |= (0x7ff & 0x3f) << 2; buf[6] = byte; return 0; }
这个头部是固定的7字节长度，所以可提前空出这7个字节供ADTS占用。
通过以上对H264和AAC的扩展数据处理，播放各种“黄金搭档”的多媒体文件、流媒体、视频点播等都应该没有问题了。
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经过验证，上述方法结合ffmpeg是可以完成解码aac的。