FFMpeg HLS动态切换分辨率

• HLS支持多分辨率，在M3U8中会写明支持的分辨率，如下（随便找的一个例子）

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=375000,RESOLUTION=640x360
360_out.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=750000,RESOLUTION=854x480
480_out.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2000000,RESOLUTION=1280x720
720_out.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=3500000,RESOLUTION=1920x1080
1080_out.m3u8
           

• 切换不同的分辨率其实就是选择不同的

  AVProgram

  ，通过AVProgram的discard控制是否启用

typedef struct AVFormatContext {
    ...
    unsigned int nb_programs;
    AVProgram **programs;
    ...
}

typedef struct AVProgram {
    int            id;
    int            flags;
    enum AVDiscard discard;        ///< selects which program to discard and which to feed to the caller
    unsigned int   *stream_index;
    unsigned int   nb_stream_indexes;
    AVDictionary *metadata;

    int program_num;
    int pmt_pid;
    int pcr_pid;
    int pmt_version;
    int64_t start_time;
    int64_t end_time;

    int64_t pts_wrap_reference;    ///< reference dts for wrap detection
    int pts_wrap_behavior;         ///< behavior on wrap detection
} AVProgram;
           

• 切换之后使用

  av_seek_frame

  到特定的时间点
• 动态切换需要注意的就是要衔接好，像字节的西平视频就比较激进切换之后马上就用新的分辨率，爱奇艺就缓和一些等缓存播放完之后再衔接到新分辨率上