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;

enum AVMediaType codec_type; 编解码器的类型 
const struct AVCodec *codec; 编解码器,初始化后不可更改
enum AVCodecID codec_id; 编解码器的id
int64_t 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
AVRational time_base; 根据该参数可以将pts转化为实践
int width, height; 每一帧的宽和高
int gop_size; 一组图片的数量，编码时用户设置，解码时不使用
enum AVPixelFormat pix_fmt; 像素格式，编码时用户设置，解码时可由用户指定，但是在分析数据会被覆盖用户的设置
int refs; 参考帧的数量
enum AVColorSpace colorspace; YUV色彩空间类型
enum AVColorRange color_range; MPEG JPEG YUV范围
int sample_rate; 采样率 仅音频
int channels; 声道数（音频）
enum AVSampleFormat sample_fmt; //采样格式
int frame_size; 每个音频帧中每个声道的采样数量
int profile;配置类型
int level;级别