ffplay: calculate target clock dynamically, make code more readable

Since target clock is based on the current A-V delay, it is better calculate it
when we actually need it rather than when we put a picture in the picture
queue.

The patch also makes a code a bit more readable by renaming some delay
variables to duration, and converting compute_target_time to a delay
calculating function which does not modify the state. Factoring out the
iteration of the pictq to standalone function is also done in this patch.
Signed-off-by: Marton Balint <cus@passwd.hu>

ffplay.c

@@ -98,9 +98,9 @@ typedef struct PacketQueue {
 
 typedef struct VideoPicture {
     double pts;                                  ///<presentation time stamp for this picture
-    double target_clock;                         ///<av_gettime() time at which this should be displayed ideally
     double duration;                             ///<expected duration of the frame
     int64_t pos;                                 ///<byte position in file
+    int skip;
     SDL_Overlay *bmp;
     int width, height; /* source height & width */
     int allocated;
@@ -197,7 +197,7 @@ typedef struct VideoState {
 
     double frame_timer;
     double frame_last_pts;
-    double frame_last_delay;
+    double frame_last_duration;
     double video_clock;                          ///<pts of last decoded frame / predicted pts of next decoded frame
     int video_stream;
     AVStream *video_st;
@@ -1071,19 +1071,9 @@ static void stream_toggle_pause(VideoState *is)
     is->paused = !is->paused;
 }
 
-static double compute_target_time(double frame_current_pts, VideoState *is)
+static double compute_target_delay(double delay, VideoState *is)
 {
-    double delay, sync_threshold, diff;
-
-    /* compute nominal delay */
-    delay = frame_current_pts - is->frame_last_pts;
-    if (delay <= 0 || delay >= 10.0) {
-        /* if incorrect delay, use previous one */
-        delay = is->frame_last_delay;
-    } else {
-        is->frame_last_delay = delay;
-    }
-    is->frame_last_pts = frame_current_pts;
+    double sync_threshold, diff;
 
     /* update delay to follow master synchronisation source */
     if (((is->av_sync_type == AV_SYNC_AUDIO_MASTER && is->audio_st) ||
@@ -1103,12 +1093,22 @@ static double compute_target_time(double frame_current_pts, VideoState *is)
                 delay = 2 * delay;
         }
     }
-    is->frame_timer += delay;
 
-    av_dlog(NULL, "video: delay=%0.3f pts=%0.3f A-V=%f\n",
-            delay, frame_current_pts, -diff);
+    av_dlog(NULL, "video: delay=%0.3f A-V=%f\n",
+            delay, -diff);
 
-    return is->frame_timer;
+    return delay;
+}
+
+static void pictq_next_picture(VideoState *is) {
+    /* update queue size and signal for next picture */
+    if (++is->pictq_rindex == VIDEO_PICTURE_QUEUE_SIZE)
+        is->pictq_rindex = 0;
+
+    SDL_LockMutex(is->pictq_mutex);
+    is->pictq_size--;
+    SDL_CondSignal(is->pictq_cond);
+    SDL_UnlockMutex(is->pictq_mutex);
 }
 
 /* called to display each frame */
@@ -1125,34 +1125,45 @@ retry:
             //nothing to do, no picture to display in the que
         } else {
             double time= av_gettime()/1000000.0;
-            double next_target;
+            double last_duration, duration, delay;
             /* dequeue the picture */
             vp = &is->pictq[is->pictq_rindex];
 
-            if(time < vp->target_clock)
+            if (vp->skip) {
+                pictq_next_picture(is);
+                goto retry;
+            }
+
+            /* compute nominal last_duration */
+            last_duration = vp->pts - is->frame_last_pts;
+            if (last_duration > 0 && last_duration < 10.0) {
+                /* if duration of the last frame was sane, update last_duration in video state */
+                is->frame_last_duration = last_duration;
+            }
+            delay = compute_target_delay(is->frame_last_duration, is);
+
+            if(time < is->frame_timer + delay)
                 return;
+
+            is->frame_last_pts = vp->pts;
+            is->frame_timer += delay;
+
             /* update current video pts */
             is->video_current_pts = vp->pts;
             is->video_current_pts_drift = is->video_current_pts - time;
             is->video_current_pos = vp->pos;
-            if(is->pictq_size > 1){
-                VideoPicture *nextvp= &is->pictq[(is->pictq_rindex+1)%VIDEO_PICTURE_QUEUE_SIZE];
-                assert(nextvp->target_clock >= vp->target_clock);
-                next_target= nextvp->target_clock;
-            }else{
-                next_target= vp->target_clock + vp->duration;
+
+            if(is->pictq_size > 1) {
+                 VideoPicture *nextvp= &is->pictq[(is->pictq_rindex+1)%VIDEO_PICTURE_QUEUE_SIZE];
+                 duration = nextvp->pts - vp->pts; // More accurate this way, 1/time_base is often not reflecting FPS
+            } else {
+                 duration = vp->duration;
             }
-            if((framedrop>0 || (framedrop && is->audio_st)) && time > next_target){
+
+            if((framedrop>0 || (framedrop && is->audio_st)) && time > is->frame_timer + duration){
                 is->skip_frames *= 1.0 + FRAME_SKIP_FACTOR;
                 if(is->pictq_size > 1){
-                    /* update queue size and signal for next picture */
-                    if (++is->pictq_rindex == VIDEO_PICTURE_QUEUE_SIZE)
-                        is->pictq_rindex = 0;
-
-                    SDL_LockMutex(is->pictq_mutex);
-                    is->pictq_size--;
-                    SDL_CondSignal(is->pictq_cond);
-                    SDL_UnlockMutex(is->pictq_mutex);
+                    pictq_next_picture(is);
                     goto retry;
                 }
             }
@@ -1205,14 +1216,7 @@ retry:
             if (!display_disable)
                 video_display(is);
 
-            /* update queue size and signal for next picture */
-            if (++is->pictq_rindex == VIDEO_PICTURE_QUEUE_SIZE)
-                is->pictq_rindex = 0;
-
-            SDL_LockMutex(is->pictq_mutex);
-            is->pictq_size--;
-            SDL_CondSignal(is->pictq_cond);
-            SDL_UnlockMutex(is->pictq_mutex);
+            pictq_next_picture(is);
         }
     } else if (is->audio_st) {
         /* draw the next audio frame */
@@ -1425,13 +1429,12 @@ static int queue_picture(VideoState *is, AVFrame *src_frame, double pts1, int64_
 
         vp->pts = pts;
         vp->pos = pos;
+        vp->skip = 0;
 
         /* now we can update the picture count */
         if (++is->pictq_windex == VIDEO_PICTURE_QUEUE_SIZE)
             is->pictq_windex = 0;
         SDL_LockMutex(is->pictq_mutex);
-        vp->target_clock= compute_target_time(vp->pts, is);
-
         is->pictq_size++;
         SDL_UnlockMutex(is->pictq_mutex);
     }
@@ -1451,7 +1454,7 @@ static int get_video_frame(VideoState *is, AVFrame *frame, int64_t *pts, AVPacke
         SDL_LockMutex(is->pictq_mutex);
         //Make sure there are no long delay timers (ideally we should just flush the que but thats harder)
         for (i = 0; i < VIDEO_PICTURE_QUEUE_SIZE; i++) {
-            is->pictq[i].target_clock= 0;
+            is->pictq[i].skip = 1;
         }
         while (is->pictq_size && !is->videoq.abort_request) {
             SDL_CondWait(is->pictq_cond, is->pictq_mutex);
@@ -1460,7 +1463,7 @@ static int get_video_frame(VideoState *is, AVFrame *frame, int64_t *pts, AVPacke
         SDL_UnlockMutex(is->pictq_mutex);
 
         is->frame_last_pts = AV_NOPTS_VALUE;
-        is->frame_last_delay = 0;
+        is->frame_last_duration = 0;
         is->frame_timer = (double)av_gettime() / 1000000.0;
         is->skip_frames = 1;
         is->skip_frames_index = 0;