如何进行分析FFmpegffplay

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代码堆栈回溯

  ffplayd.exe!video_image_display(VideoState * is) 行 1036 C
  ffplayd.exe!video_display(VideoState * is) 行 1371 C
  ffplayd.exe!video_refresh(void * opaque, double * remaining_time) 行 1690 C
  ffplayd.exe!refresh_loop_wait_event(VideoState * is, SDL_Event * event) 行 3229 C
  ffplayd.exe!event_loop(VideoState * cur_stream) 行 3269 C
  ffplayd.exe!main(int argc, char * * argv) 行 3768 C

调用 SDL_RenderCopyEx(renderer, is->vid_texture, NULL, &rect, 0, NULL, vp->flip_v ? SDL_FLIP_VERTICAL : 0)实现界面的渲染
渲染的时机非常重要

1）refresh_loop_wait_event函数剖析

static void refresh_loop_wait_event(VideoState *is, SDL_Event *event) {
    double remaining_time = 0.0;
   //调用该函数搜集输入设备的事件（例如键盘输入，鼠标移动），然后存放在事件队列中，等待SDL_PeepEvents获取事件
    SDL_PumpEvents();
  //SDL_GETEVENT操作指定的SDL_PeepEvents会读取事件队列中的事件消息，并且是将读取的事件移除出队列
  //while循环!说明了只要事件队列有消息，优先执行队列中的事件，然后才进行视频的渲染
    while (!SDL_PeepEvents(event, 1, SDL_GETEVENT, SDL_FIRSTEVENT, SDL_LASTEVENT)) {
        if (!cursor_hidden && av_gettime_relative() - cursor_last_shown > CURSOR_HIDE_DELAY) {
            SDL_ShowCursor(0);
            cursor_hidden = 1;
        }
        if (remaining_time > 0.0)
            av_usleep((int64_t)(remaining_time * 1000000.0));
        remaining_time = REFRESH_RATE;
        if (is->show_mode != SHOW_MODE_NONE && (!is->paused || is->force_refresh))
            video_refresh(is, &remaining_time);
        //重新搜索输入设备的事件，如果屏蔽掉该函数的调用，将会导致键盘的输入无法进行事件队列，导致键盘输入无效，例如尝试按下q停止视频播放
        SDL_PumpEvents();
    }
}

static void video_refresh(void *opaque, double *remaining_time)
{
    VideoState *is = opaque;
    double time;

    Frame *sp, *sp2;

    if (!is->paused && get_master_sync_type(is) == AV_SYNC_EXTERNAL_CLOCK && is->realtime)
        check_external_clock_speed(is);

   //如果不是音频数据，也就是字幕或者声音显示或者播放
    if (!display_disable && is->show_mode != SHOW_MODE_VIDEO && is->audio_st) {
        time = av_gettime_relative() / 1000000.0;
        if (is->force_refresh || is->last_vis_time + rdftspeed < time) {
            video_display(is);
            is->last_vis_time = time;
        }
        *remaining_time = FFMIN(*remaining_time, is->last_vis_time + rdftspeed - time);
    }

    if (is->video_st) {
retry:
        if (frame_queue_nb_remaining(&is->pictq) == 0) {
            // nothing to do, no picture to display in the queue
        } else {
            double last_duration, duration, delay;
            Frame *vp, *lastvp;

            /* dequeue the picture */
            lastvp = frame_queue_peek_last(&is->pictq);
            vp = frame_queue_peek(&is->pictq);

            if (vp->serial != is->videoq.serial) {
                frame_queue_next(&is->pictq);
                goto retry;
            }

            if (lastvp->serial != vp->serial)
                is->frame_timer = av_gettime_relative() / 1000000.0;

            if (is->paused)
                goto display;

            /* compute nominal last_duration */
            last_duration = vp_duration(is, lastvp, vp);
            delay = compute_target_delay(last_duration, is);

            time= av_gettime_relative()/1000000.0;
            if (time < is->frame_timer + delay) {
                *remaining_time = FFMIN(is->frame_timer + delay - time, *remaining_time);
                goto display;
            }

            is->frame_timer += delay;
            if (delay > 0 && time - is->frame_timer > AV_SYNC_THRESHOLD_MAX)
                is->frame_timer = time;

            SDL_LockMutex(is->pictq.mutex);
            if (!isnan(vp->pts))
                update_video_pts(is, vp->pts, vp->pos, vp->serial);
            SDL_UnlockMutex(is->pictq.mutex);

            if (frame_queue_nb_remaining(&is->pictq) > 1) {
                Frame *nextvp = frame_queue_peek_next(&is->pictq);
                duration = vp_duration(is, vp, nextvp);
                if(!is->step && (framedrop>0 || (framedrop && get_master_sync_type(is) != AV_SYNC_VIDEO_MASTER)) && time > is->frame_timer + duration){
                    is->frame_drops_late++;
                    frame_queue_next(&is->pictq);
                    goto retry;
                }
            }

            if (is->subtitle_st) {
                    while (frame_queue_nb_remaining(&is->subpq) > 0) {
                        sp = frame_queue_peek(&is->subpq);

                        if (frame_queue_nb_remaining(&is->subpq) > 1)
                            sp2 = frame_queue_peek_next(&is->subpq);
                        else
                            sp2 = NULL;

                        if (sp->serial != is->subtitleq.serial
                                || (is->vidclk.pts > (sp->pts + ((float) sp->sub.end_display_time / 1000)))
                                || (sp2 && is->vidclk.pts > (sp2->pts + ((float) sp2->sub.start_display_time / 1000))))
                        {
                            if (sp->uploaded) {
                                int i;
                                for (i = 0; i < sp->sub.num_rects; i++) {
                                    AVSubtitleRect *sub_rect = sp->sub.rects[i];
                                    uint8_t *pixels;
                                    int pitch, j;

                                    if (!SDL_LockTexture(is->sub_texture, (SDL_Rect *)sub_rect, (void **)&pixels, &pitch)) {
                                        for (j = 0; j < sub_rect->h; j++, pixels += pitch)
                                            memset(pixels, 0, sub_rect->w << 2);
                                        SDL_UnlockTexture(is->sub_texture);
                                    }
                                }
                            }
                            frame_queue_next(&is->subpq);
                        } else {
                            break;
                        }
                    }
            }

            frame_queue_next(&is->pictq);
            is->force_refresh = 1;

            if (is->step && !is->paused)
                stream_toggle_pause(is);
        }
display:
        /* display picture */
        if (!display_disable && is->force_refresh && is->show_mode == SHOW_MODE_VIDEO && is->pictq.rindex_shown)
            video_display(is);
    }
    is->force_refresh = 0;
    if (show_status) {
        static int64_t last_time;
        int64_t cur_time;
        int aqsize, vqsize, sqsize;
        double av_diff;

        cur_time = av_gettime_relative();
        if (!last_time || (cur_time - last_time) >= 30000) {
            aqsize = 0;
            vqsize = 0;
            sqsize = 0;
            if (is->audio_st)
                aqsize = is->audioq.size;
            if (is->video_st)
                vqsize = is->videoq.size;
            if (is->subtitle_st)
                sqsize = is->subtitleq.size;
            av_diff = 0;
            if (is->audio_st && is->video_st)
                av_diff = get_clock(&is->audclk) - get_clock(&is->vidclk);
            else if (is->video_st)
                av_diff = get_master_clock(is) - get_clock(&is->vidclk);
            else if (is->audio_st)
                av_diff = get_master_clock(is) - get_clock(&is->audclk);
            av_log(NULL, AV_LOG_INFO,
                   "%7.2f %s:%7.3f fd=%4d aq=%5dKB vq=%5dKB sq=%5dB f=%"PRId64"/%"PRId64"   \r",
                   get_master_clock(is),
                   (is->audio_st && is->video_st) ? "A-V" : (is->video_st ? "M-V" : (is->audio_st ? "M-A" : "   ")),
                   av_diff,
                   is->frame_drops_early + is->frame_drops_late,
                   aqsize / 1024,
                   vqsize / 1024,
                   sqsize,
                   is->video_st ? is->viddec.avctx->pts_correction_num_faulty_dts : 0,
                   is->video_st ? is->viddec.avctx->pts_correction_num_faulty_pts : 0);
            fflush(stdout);
            last_time = cur_time;
        }
    }
}

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