avformat_seek_file及其flag含义

我们从ijk中seek的处理流程来看ffmpeg的这个问题

int ffp_seek_to_l(FFPlayer *ffp, long msec)
{
    assert(ffp);
    VideoState *is = ffp->is;
    int64_t start_time = 0;
    int64_t seek_pos = milliseconds_to_fftime(msec);
    int64_t duration = milliseconds_to_fftime(ffp_get_duration_l(ffp));

    if (!is)
        return EIJK_NULL_IS_PTR;
	//add by hxk
	if(ffp->loopStart != 0 && ffp->loopEnd != INT_MAX){
		//use setLooping
        setLooping,     
	} else {
	    //not use setLooping
		resetLoopStartAndEnd(ffp);
	}
	//add end

    if (duration > 0 && seek_pos >= duration && ffp->enable_accurate_seek) {
        toggle_pause(ffp, 1);
        ffp_notify_msg1(ffp, FFP_MSG_COMPLETED);
        return 0;
    }

    start_time = is->ic->start_time;
    if (start_time > 0 && start_time != AV_NOPTS_VALUE)
        seek_pos += start_time;

    // FIXME: 9 seek by bytes
    // FIXME: 9 seek out of range
    // FIXME: 9 seekable
    av_log(ffp, AV_LOG_DEBUG, "stream_seek %"PRId64"(%d) + %"PRId64", \n", seek_pos, (int)msec, start_time);
    stream_seek(is, seek_pos, 0, 0);
    return 0;
}

看一下stream_Seek/ff_ffplay.c函数，可以看到ijk中没有处理seek_flags

/* seek in the stream */
static void stream_seek(VideoState *is, int64_t pos, int64_t rel, int seek_by_bytes)
{
    if (!is->seek_req) {
        is->seek_pos = pos;
        is->seek_rel = rel;
        is->seek_flags &= ~AVSEEK_FLAG_BYTE;
        if (seek_by_bytes)
            is->seek_flags |= AVSEEK_FLAG_BYTE;
        is->seek_req = 1;
        SDL_CondSignal(is->continue_read_thread);
    }
}

在read_thread/ff_ffplay.c中会获取这个flag来使用 avformat_seek_file函数跳转位置。

ffp_toggle_buffering(ffp, 1);//hxk:Open the buffer and start playing.
            ffp_notify_msg3(ffp, FFP_MSG_BUFFERING_UPDATE, 0, 0);
            /**跳转到逼近ts时间点，并且在seek_min和seek_max范围之内,这里的flag是0*/
            ret = avformat_seek_file(is->ic, -1, seek_min, seek_target, seek_max, is->seek_flags);
            if (ret < 0) {
                av_log(NULL, AV_LOG_ERROR,
                       "%s: error while seeking\n", is->ic->filename);
            } else {

那么ffmpeg中flag可以设置哪些呢？

flag值:

#deflagfine AVSEEK_FLAG_BACKWARD    1 ///< seek backward
#define AVSEEK_FLAG_BYTE                     2 ///< seeking based on position in bytes
#define AVSEEK_FLAG_ANY                       4 ///< seek to any frame, even non-keyframes
#define AVSEEK_FLAG_FRAME                  8 ///< seeking based on frame number

AVSEEK_FLAG_BACKWARD//是seek到请求的timestamp之前最近的关键帧

AVSEEK_FLAG_BYTE //    是基于字节位置的查找 

AVSEEK_FLAG_ANY  //是可以seek到任意帧，注意不一定是关键帧，因此使用时可能会导致花屏    

AVSEEK_FLAG_FRAME//是基于帧数量快进          

上面的几个flag目前我都没使用过。