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AVSream中我们可以使用codec得到AVCodecContext指针，该结构体代表了AVStream中持有的codec相关的上下文，包含了众多编解码器需要的参数信息。一个AVStream对应一个AVCodecContext指针。但是，如果你使用较高的FFmpeg版本就应该发现，codec成员已经不受支持，也就是在AVStream中该成员已经被废弃，而且，AVCodecContext由于太过复杂，FFmpeg的维护者也开始逐渐拆分这个结构体的功能，准备废弃AVCodecContext。目前，官方推荐使用AVCodecParameters这个结构体来替代它。  其中，我们常用到的成员有： ```cpp //(1)编解码器类型，音频/视频/字幕 enum AVMediaType codec_type; //其中，codec_type定义如下： enum AVMediaType { AVMEDIA_TYPE_UNKNOWN = -1, ///< Usually treated as AVMEDIA_TYPE_DATA AVMEDIA_TYPE_VIDEO, AVMEDIA_TYPE_AUDIO, AVMEDIA_TYPE_DATA, ///< Opaque data information usually continuous AVMEDIA_TYPE_SUBTITLE, AVMEDIA_TYPE_ATTACHMENT, ///< Opaque data information usually sparse AVMEDIA_TYPE_NB }; //(2)像素格式(YUV420等)/音频采样格式 int format; //(3)编解码器的id //使用函数avcodec_get_name(codec_id)可以获得视频/音频编码格式 enum AVCodecID codec_id; //(4)平均码率/比特率 int64_t bit_rate; //(5)视频宽度/高度 int width; int height; //(6) 音频通道数 int sample_rate; //(7)音频帧率 int frame_size; ``` 对于AVCodecParameters结构体，其定义如下： ```cpp /** * 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; /** * The number of bits per sample in the codedwords. * * This is basically the bitrate per sample. It is mandatory for a bunch of * formats to actually decode them. It's the number of bits for one sample in * the actual coded bitstream. * * This could be for example 4 for ADPCM * For PCM formats this matches bits_per_raw_sample * Can be 0 */ int bits_per_coded_sample; /** * This is the number of valid bits in each output sample. If the * sample format has more bits, the least significant bits are additional * padding bits, which are always 0. Use right shifts to reduce the sample * to its actual size. For example, audio formats with 24 bit samples will * have bits_per_raw_sample set to 24, and format set to AV_SAMPLE_FMT_S32. * To get the original sample use "(int32_t)sample >> 8"." * * For ADPCM this might be 12 or 16 or similar * Can be 0 */ int bits_per_raw_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; ``` Last modification：June 15th, 2021 at 06:05 pm © 允许规范转载