ffmpeg音频解码av_frame_alloc

av_frame_alloc函数用于为AVFrame结构体分配内存空间，AVFrame结构体用于存储解码后的音视频数据。在音频解码中，可以通过调用该函数为AVFrame结构体分配内存空间，然后将解码后的音频数据存储到该结构体中，最后再进行后续的处理操作。

具体使用方法如下：

AVFrame *frame = av_frame_alloc();
if (!frame) {
    // 内存分配失败处理
}

其中，AVFrame结构体的定义如下：

typedef struct AVFrame {
    /**
     * pointers to the data planes/channels.
     * This might be different from the first allocated byte
     */
    uint8_t *data[AV_NUM_DATA_POINTERS];
    /**
     * For video, size in bytes of each picture line.
     * For audio, size in bytes of each plane.
     */
    int linesize[AV_NUM_DATA_POINTERS];
    /**
     * pointers to the start of each picture line.
     * This is used for both video and audio.
     */
    uint8_t **extended_data;
    /**
     * width and height of the video frame
     */
    int width, height;
    /**
     * number of audio samples (per channel) described by this frame
     */
    int nb_samples;
    /**
     * format of the frame, -1 if unknown or unset
     * Values correspond to enum AVPixelFormat for video frames,
     * enum AVSampleFormat for audio)
     */
    int format;
    /**
     * 1 -> keyframe, 0-> not
     */
    int key_frame;
    /**
     * Picture type of the frame.
     */
    enum AVPictureType pict_type;
    /**
     * Quality (between 1 (good) and FF_LAMBDA_MAX (bad)).
     */
    int quality;
    /**
     * for AV_PIX_FMT_*_BE formats, linesize alignment
     */
    int64_t     best_effort_timestamp;
    /**
     * PTS copied from the AVPacket that was decoded to produce this frame.
     */
    int64_t     pkt_pts;
    /**
     * DTS copied from the AVPacket that triggered returning this frame.
     */
    int64_t     pkt_dts;
    /**
     * duration of the corresponding packet, expressed in
     * AVStream->time_base units, 0 if unknown.
     */
    int64_t     pkt_duration;
    uint64_t    metadata;
    int         decode_error_flags;
    /**
     * number of audio channels
     */
    int         channels;
    /**
     * size of the corresponding packet containing the compressed
     * frame. It is set to a negative value if unknown.
     */
    int         pkt_size;
    /**
     * data type
     */
    enum AVSampleFormat  sample_fmt;
    /**
     * presentation timestamp in timebase units
     * (time when frame should be shown to user)
     * If AV_NOPTS_VALUE then frame_rate = 1/time_base will be assumed.
     */
    int64_t     pts;
    /**
     * reordered PTS from the last AVPacket that has been input into the decoder
     */
    int64_t     best_effort_timestamp;
    /**
     * sample aspect ratio (0 if unknown)
     * - encoding: Set by user.
     * - decoding: Set by libavcodec.
     */
    AVRational  sample_aspect_ratio;
    /**
     * motion vector table, used for MPEG1/2/4 and H.263 decoding
     */
    struct AVPanScan *pan_scan;
    /**
     * macroblock decision mode
     */
    int         coded_picture_number;
    int         display_picture_number;
    /**
     * quality (between 1 (good) and FF_LAMBDA_MAX (bad))
     */
    int         quality;
    /**
     * buffer age (1->was last buffer and dint change, 2->..., ...)
     */
    int         age;
    /**
     * is this picture used as reference
     */
    int reference;
    /**
     * QP table
     */
    int8_t *qp_table_buf;
    /**
     * QP store stride
     */
    int     qp_table_linesize;
    /**
     * QP values for each macroblock
     */
    int8_t *qp_table;
    /**
     * For hwaccel-format frames, this should be a reference to the
     * AVHWFramesContext describing the frame.
     * For normal-format frames, this should be NULL.
     */
    AVBufferRef *hw_frames_ctx;
} AVFrame;

需要注意的是，AVFrame结构体中的成员变量很多，具体使用哪些成员变量取决于具体的应用场景和需求。