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/** * This struct describes the properties of an encoded stream. * * sizeof(AVCodecParameters) is not a part of the public ABI, this struct must * be allocated with avcodec_parameters_alloc() and freed with * avcodec_parameters_free(). */typedef struct AVCodecParameters { /** * General type of the encoded data. */ enum AVMediaType codec_type; /** * Specific type of the encoded data (the codec used). */ enum AVCodecID codec_id; /** * Additional information about the codec (corresponds to the AVI FOURCC). */ uint32_t codec_tag; /** * Extra binary data needed for initializing the decoder, codec-dependent. * * Must be allocated with av_malloc() and will be freed by * avcodec_parameters_free(). The allocated size of extradata must be at * least extradata_size + AV_INPUT_BUFFER_PADDING_SIZE, with the padding * bytes zeroed. */ uint8_t *extradata; /** * Size of the extradata content in bytes. */ int extradata_size; /** * - video: the pixel format, the value corresponds to enum AVPixelFormat. * - audio: the sample format, the value corresponds to enum AVSampleFormat. */ int format; /** * The average bitrate of the encoded data (in bits per second). */ int64_t bit_rate; int bits_per_coded_sample; /** * Codec-specific bitstream restrictions that the stream conforms to. */ int profile; int level; /** * Video only. The dimensions of the video frame in pixels. */ int width; int height; /** * Video only. The aspect ratio (width / height) which a single pixel * should have when displayed. * * When the aspect ratio is unknown / undefined, the numerator should be * set to 0 (the denominator may have any value). */ AVRational sample_aspect_ratio; /** * Video only. The order of the fields in interlaced video. */ enum AVFieldOrder field_order; /** * Video only. Additional colorspace characteristics. */ enum AVColorRange color_range; enum AVColorPrimaries color_primaries; enum AVColorTransferCharacteristic color_trc; enum AVColorSpace color_space; enum AVChromaLocation chroma_location; /** * Video only. Number of delayed frames. */ int video_delay; /** * Audio only. The channel layout bitmask. May be 0 if the channel layout is * unknown or unspecified, otherwise the number of bits set must be equal to * the channels field. */ uint64_t channel_layout; /** * Audio only. The number of audio channels. */ int channels; /** * Audio only. The number of audio samples per second. */ int sample_rate; /** * Audio only. The number of bytes per coded audio frame, required by some * formats. * * Corresponds to nBlockAlign in WAVEFORMATEX. */ int block_align; /** * Audio only. Audio frame size, if known. Required by some formats to be static. */ int frame_size; /** * Audio only. The amount of padding (in samples) 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. */ int initial_padding; /** * Audio only. The amount of padding (in samples) appended by the encoder to * the end of the audio. I.e. this number of decoded samples must be * discarded by the caller from the end of the stream to get the original * audio without any trailing padding. */ int trailing_padding; /** * Audio only. Number of samples to skip after a discontinuity. */ int seek_preroll;} AVCodecParameters; 乍眼一看，AVCodecParameters与AVCodecContext里的参数有很多相同的，但是没有函数。看来伟大的极客们，是想把一些编解码器的参数从AVCodecContext分离出来，因为AVCodecContext这个结构体实在是太大了。 enum AVMediaType codec_type：编解码器的类型（视频，音频...） enum AVCodecID codec_id：标示特定的编解码器 int format：像素格式/采样数据格式 int bit_rate：平均比特率 uint8_t *extradata; int extradata_size：针对特定编码器包含的附加信息（例如对于H.264解码器来说，存储SPS，PPS等） int width, height：如果是视频的话，代表宽和高 int refs：运动估计参考帧的个数（H.264的话会有多帧，MPEG2这类的一般就没有了） int sample_rate：采样率（音频） uint64_t channel_layout：声道格式 int channels：声道数（音频） int profile：型（H.264里面就有，其他编码标准应该也有） int level：级（和profile差不太多）
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