ijkplayer源码---seekTo

我们要进行音视频文件的seek操作，又是怎么做的呢？

通过下面的流程图我们可以清晰的看到怎样进行的操作

 我们对

ffp_seek_to_l进行分析

int ffp_seek_to_l(FFPlayer *ffp, long msec)
{
    assert(ffp);
    VideoState *is = ffp->is;
    int64_t start_time = 0;
    //转换成要跳转的时间基和总时长的事件基   msec /1000 * AV_TIME_BASE  AV_TIME_BASE代表1秒
    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;

    //跳转的位置大于duration，暂停
    if (duration > 0 && seek_pos >= duration && ffp->enable_accurate_seek) {
        toggle_pause(ffp, 1);
        ffp_notify_msg1(ffp, FFP_MSG_COMPLETED);
        return 0;
    }

    //第一帧开始的事件，用AV_TIME_BASE作为单位
    start_time = is->ic->start_time;
    //跳转位置目前我们知道seek_pos是与第一帧的时间的偏移量，我们要计算一个绝对值
    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;
}

这个函数就是将跳转的时间，换成相对于第一帧图像的以时间基为单位的绝对值。‘

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);
    }
}

这个函数就是对seek相关的变量赋值

下面的函数式实际的seek操作函数

static int read_thread(void *arg)
{
        .....
         for (;;) {
        ......
             if (is->seek_req) {
            int64_t seek_target = is->seek_pos;
            int64_t seek_min    = is->seek_rel > 0 ? seek_target - is->seek_rel + 2: INT64_MIN;
            int64_t seek_max    = is->seek_rel < 0 ? seek_target - is->seek_rel - 2: INT64_MAX;
// FIXME the +-2 is due to rounding being not done in the correct direction in generation
//      of the seek_pos/seek_rel variables

            ffp_toggle_buffering(ffp, 1);
            ffp_notify_msg3(ffp, FFP_MSG_BUFFERING_UPDATE, 0, 0);
            av_log(NULL, AV_LOG_ERROR, "yuanxuzhen is->seek_flags=%d", is->seek_flags);
            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 {
                if (is->audio_stream >= 0) {
                    packet_queue_flush(&is->audioq);
                    packet_queue_put(&is->audioq, &flush_pkt);
                    // TODO: clear invaild audio data
                    // SDL_AoutFlushAudio(ffp->aout);
                }
                if (is->subtitle_stream >= 0) {
                    packet_queue_flush(&is->subtitleq);
                    packet_queue_put(&is->subtitleq, &flush_pkt);
                }
                if (is->video_stream >= 0) {
                    if (ffp->node_vdec) {
                        ffpipenode_flush(ffp->node_vdec);
                    }
                    packet_queue_flush(&is->videoq);
                    packet_queue_put(&is->videoq, &flush_pkt);
                }
                if (is->seek_flags & AVSEEK_FLAG_BYTE) {
                   set_clock(&is->extclk, NAN, 0);
                } else {
                   set_clock(&is->extclk, seek_target / (double)AV_TIME_BASE, 0);
                }

                is->latest_video_seek_load_serial = is->videoq.serial;
                is->latest_audio_seek_load_serial = is->audioq.serial;
                is->latest_seek_load_start_at = av_gettime();
            }
            ffp->dcc.current_high_water_mark_in_ms = ffp->dcc.first_high_water_mark_in_ms;
            is->seek_req = 0;
            is->queue_attachments_req = 1;
            is->eof = 0;
#ifdef FFP_MERGE
            if (is->paused)
                step_to_next_frame(is);
#endif
            completed = 0;
            SDL_LockMutex(ffp->is->play_mutex);
            if (ffp->auto_resume) {
                is->pause_req = 0;
                if (ffp->packet_buffering)
                    is->buffering_on = 1;
                ffp->auto_resume = 0;
                stream_update_pause_l(ffp);
            }
            if (is->pause_req)
                step_to_next_frame_l(ffp);
            SDL_UnlockMutex(ffp->is->play_mutex);

            if (ffp->enable_accurate_seek) {
                is->drop_aframe_count = 0;
                is->drop_vframe_count = 0;
                SDL_LockMutex(is->accurate_seek_mutex);
                if (is->video_stream >= 0) {
                    is->video_accurate_seek_req = 1;
                }
                if (is->audio_stream >= 0) {
                    is->audio_accurate_seek_req = 1;
                }
                SDL_CondSignal(is->audio_accurate_seek_cond);
                SDL_CondSignal(is->video_accurate_seek_cond);
                SDL_UnlockMutex(is->accurate_seek_mutex);
            }

            ffp_notify_msg3(ffp, FFP_MSG_SEEK_COMPLETE, (int)fftime_to_milliseconds(seek_target), ret);
            ffp_toggle_buffering(ffp, 1);
        }


        ......            

}
        .....
}

我们可以看到avformat_seek_file这样就对音视频进行了seek