8、ffplay字幕解碼及渲染源碼分析

ffplay字幕解碼及渲染源碼分析

字幕解碼邏輯

static int subtitle_thread(void *arg)
{
    VideoState *is = arg;
    Frame *sp;
    int got_subtitle;
    double pts;

    for (;;) {
        if (!(sp = frame_queue_peek_writable(&is->subpq)))//FrameQueue中獲取一個可用的Frame節點
            return 0;

        if ((got_subtitle = decoder_decode_frame(&is->subdec, NULL, &sp->sub)) < 0)
            break;

        pts = 0;

        if (got_subtitle && sp->sub.format == 0) {
            if (sp->sub.pts != AV_NOPTS_VALUE)
                pts = sp->sub.pts / (double)AV_TIME_BASE;//pts轉換爲秒
            sp->pts = pts;
            sp->serial = is->subdec.pkt_serial;
            sp->width = is->subdec.avctx->width;
            sp->height = is->subdec.avctx->height;
            sp->uploaded = 0;

            /* now we can update the picture count */
            frame_queue_push(&is->subpq);
        } else if (got_subtitle) {
            avsubtitle_free(&sp->sub);
        }
    }
    return 0;
}

字幕渲染邏輯

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);

    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))))
                        {
                            /*
                            該部分去除過時的字幕數據幀,滿足以下條件之一進入該段代碼塊:
                            1、PacketQueue flush序列號改變
                            2、當前的字幕幀的結束顯示的pts小於當前視頻的pts
                            3、下一幀開始時間小於視頻的pts
                            */

                            if (sp->uploaded) {
                                /*
                                前面有字幕顯示，清除之前顯示的字幕
                                */
                                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)
                                        {
                                            /*
                                           由於texture像素格式爲SDL_PIXELFORMAT_ARGB8888，每一個像素佔4字節,
                                           因此每一行的數據大小爲sub_rect->w*4等價於sub_rect->w左移2位
                                            */
                                            memset(pixels, 0, sub_rect->w << 2);
                                        }
                                        SDL_UnlockTexture(is->sub_texture);
                                    }
                                }
                            }
                            frame_queue_next(&is->subpq);//移除一幀數據
                        } 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;
}

static void video_image_display(VideoState *is)
{
    Frame *vp;
    Frame *sp = NULL;
    SDL_Rect rect;
	

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

            if (vp->pts >= sp->pts + ((float) sp->sub.start_display_time / 1000)) {
                //視頻pts大於了字幕顯示的pts，進入代碼塊
                if (!sp->uploaded) {
                    uint8_t* pixels[4];
                    int pitch[4];
                    int i;
                    if (!sp->width || !sp->height) {
                        sp->width = vp->width;
                        sp->height = vp->height;
                    }
                    //有透明度，設置SDL_BLENDMODE_BLEND
                    if (realloc_texture(&is->sub_texture, SDL_PIXELFORMAT_ARGB8888, sp->width, sp->height, SDL_BLENDMODE_BLEND, 1) < 0)
                        return;

                    for (i = 0; i < sp->sub.num_rects; i++) {
                        AVSubtitleRect *sub_rect = sp->sub.rects[i];

                        sub_rect->x = av_clip(sub_rect->x, 0, sp->width );
                        sub_rect->y = av_clip(sub_rect->y, 0, sp->height);
                        sub_rect->w = av_clip(sub_rect->w, 0, sp->width  - sub_rect->x);
                        sub_rect->h = av_clip(sub_rect->h, 0, sp->height - sub_rect->y);

                        is->sub_convert_ctx = sws_getCachedContext(is->sub_convert_ctx,
                            sub_rect->w, sub_rect->h, AV_PIX_FMT_PAL8,
                            sub_rect->w, sub_rect->h, AV_PIX_FMT_BGRA,
                            0, NULL, NULL, NULL);
                        if (!is->sub_convert_ctx) {
                            av_log(NULL, AV_LOG_FATAL, "Cannot initialize the conversion context\n");
                            return;
                        }
                        if (!SDL_LockTexture(is->sub_texture, (SDL_Rect *)sub_rect, (void **)pixels, pitch)) {
                            sws_scale(is->sub_convert_ctx, (const uint8_t * const *)sub_rect->data, sub_rect->linesize,
                                      0, sub_rect->h, pixels, pitch);
                            SDL_UnlockTexture(is->sub_texture);
                        }
                    }
                    sp->uploaded = 1;
                }
            } else { 
                   sp = NULL;
            }
        }
    }

    calculate_display_rect(&rect, is->xleft, is->ytop, is->width, is->height, vp->width, vp->height, vp->sar);
  
    略視頻渲邏輯...
  
    if (sp) {
#if USE_ONEPASS_SUBTITLE_RENDER
        SDL_RenderCopy(renderer, is->sub_texture, NULL, &rect);
#else
        int i;
        double xratio = (double)rect.w / (double)sp->width;
        double yratio = (double)rect.h / (double)sp->height;
        for (i = 0; i < sp->sub.num_rects; i++) {
            SDL_Rect *sub_rect = (SDL_Rect*)sp->sub.rects[i];
            SDL_Rect target = {.x = rect.x + sub_rect->x * xratio,
                               .y = rect.y + sub_rect->y * yratio,
                               .w = sub_rect->w * xratio,
                               .h = sub_rect->h * yratio};
            SDL_RenderCopy(renderer, is->sub_texture, sub_rect, &target);
        }
#endif
    }
}