AVFrame

AVFrame 是 FFmpeg 中表示视频或音频帧的结构体，它包含了一帧的所有信息，如像素数据、采样数据、时间戳、宽高等等。在 FFmpeg 中，解码后的数据一般都会被存储在 AVFrame 中，然后再进行后续的处理。

AVFrame 的定义如下：

typedef struct AVFrame {
    /**
     * Pointer to the picture/channel planes.
     * This might be different from the first allocated byte
     */
    uint8_t *data[AV_NUM_DATA_POINTERS];

    /**
     * Size, in bytes, of the data for each plane.
     */
    int linesize[AV_NUM_DATA_POINTERS];

    /**
     * pointers to the samples in uint8_t **
     * planar audio only
     */
    uint8_t **extended_data;

    /**
     * Width and height of the video frame
     */
    int width, height;

    /**
     * Format of the video frame
     */
    enum AVPixelFormat format;

    /**
     * Sample rate of the audio frame
     */
    int sample_rate;

    /**
     * Number of audio samples (per channel) described by this frame
     */
    int nb_samples;

    /**
     * Channel layout of the audio frame
     */
    uint64_t channel_layout;

    /**
     * Presentation timestamp in timebase units (time when frame should be shown to user).
     */
    int64_t pts;

    /**
     * PTS copied from the AVPacket that was decoded to produce this frame
     */
    int64_t pkt_pts;

    /**
     * Duration of this frame in timebase units (0 if unknown or undefined).
     */
    int64_t duration;

    /**
     * Flags indicating which frame properties are present
     */
    int flags;

    /**
     * A Boolean value indicating whether the frame is a key frame (1) or not (0).
     */
    int key_frame;

    /**
     * A pointer to the next frame in the linked list.
     */
    struct AVFrame *next;

    /**
     * The number of elements in the extended_data array.
     */
    int8_t *extended_data_size;

    /**
     * Metadata for the frame.
     */
    AVDictionary *metadata;
} AVFrame;

AVFrame 中最重要的是 data 和 linesize 这两个成员，它们表示每个像素或采样数据的地址和大小，可以通过它们来访问帧中的数据。同时，AVFrame 中还包含了一些其他的信息，如帧的宽高、格式、时间戳等等。