ffplay: reimplement early frame drop

This patch reimplements early frame drop, it is now based on the current
difference between the master clock and the video clock, and the pts of the
current and the last displayed (or skipped) frame.  If the frame to be added to
the queue is late after decoding, then we drop it early because later we would
drop it anyway (unless it is the only frame in the picture queue).

The current approach has only one downside that I know of, it does not handle
well when the filters are changing significantly the pts of the frames, because
we compare pts values from filtered and unfiltered frames.

We also start using the pictq_mutex to ensure consistent video_current_pts,
video_current_pts_drift, frame_last_pts, frame_last_dropped_pts and
frame_last_dropped_pos values.

Signed-off-by: Marton Balint <cus@passwd.hu>

ffplay.c

@@ -197,6 +197,8 @@ typedef struct VideoState {
     double frame_timer;
     double frame_last_pts;
     double frame_last_duration;
+    double frame_last_dropped_pts;
+    int64_t frame_last_dropped_pos;
     double video_clock;                          ///<pts of last decoded frame / predicted pts of next decoded frame
     int video_stream;
     AVStream *video_st;
@@ -1102,20 +1104,35 @@ static void pictq_next_picture(VideoState *is) {
     SDL_UnlockMutex(is->pictq_mutex);
 }
 
+static void update_video_pts(VideoState *is, double pts, int64_t pos) {
+    double time = av_gettime() / 1000000.0;
+    /* update current video pts */
+    is->video_current_pts = pts;
+    is->video_current_pts_drift = is->video_current_pts - time;
+    is->video_current_pos = pos;
+    is->frame_last_pts = pts;
+}
+
 /* called to display each frame */
 static void video_refresh(void *opaque)
 {
     VideoState *is = opaque;
     VideoPicture *vp;
+    double time;
 
     SubPicture *sp, *sp2;
 
     if (is->video_st) {
 retry:
         if (is->pictq_size == 0) {
+            SDL_LockMutex(is->pictq_mutex);
+            if (is->frame_last_dropped_pts != AV_NOPTS_VALUE && is->frame_last_dropped_pts > is->frame_last_pts) {
+                update_video_pts(is, is->frame_last_dropped_pts, is->frame_last_dropped_pos);
+                is->frame_last_dropped_pts = AV_NOPTS_VALUE;
+            }
+            SDL_UnlockMutex(is->pictq_mutex);
             //nothing to do, no picture to display in the que
         } else {
-            double time= av_gettime()/1000000.0;
             double last_duration, duration, delay;
             /* dequeue the picture */
             vp = &is->pictq[is->pictq_rindex];
@@ -1133,17 +1150,16 @@ retry:
             }
             delay = compute_target_delay(is->frame_last_duration, is);
 
+            time= av_gettime()/1000000.0;
             if(time < is->frame_timer + delay)
                 return;
 
-            is->frame_last_pts = vp->pts;
             if (delay > 0)
                 is->frame_timer += delay * FFMAX(1, floor((time-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;
+            SDL_LockMutex(is->pictq_mutex);
+            update_video_pts(is, vp->pts, vp->pos);
+            SDL_UnlockMutex(is->pictq_mutex);
 
             if(is->pictq_size > 1) {
                  VideoPicture *nextvp= &is->pictq[(is->pictq_rindex+1)%VIDEO_PICTURE_QUEUE_SIZE];
@@ -1448,17 +1464,20 @@ static int get_video_frame(VideoState *is, AVFrame *frame, int64_t *pts, AVPacke
             SDL_CondWait(is->pictq_cond, is->pictq_mutex);
         }
         is->video_current_pos = -1;
-        SDL_UnlockMutex(is->pictq_mutex);
-
         is->frame_last_pts = AV_NOPTS_VALUE;
         is->frame_last_duration = 0;
         is->frame_timer = (double)av_gettime() / 1000000.0;
+        is->frame_last_dropped_pts = AV_NOPTS_VALUE;
+        SDL_UnlockMutex(is->pictq_mutex);
+
         return 0;
     }
 
     avcodec_decode_video2(is->video_st->codec, frame, &got_picture, pkt);
 
     if (got_picture) {
+        int ret = 1;
+
         if (decoder_reorder_pts == -1) {
             *pts = frame->best_effort_timestamp;
         } else if (decoder_reorder_pts) {
@@ -1471,8 +1490,25 @@ static int get_video_frame(VideoState *is, AVFrame *frame, int64_t *pts, AVPacke
             *pts = 0;
         }
 
-        return 1;
+        if (((is->av_sync_type == AV_SYNC_AUDIO_MASTER && is->audio_st) || is->av_sync_type == AV_SYNC_EXTERNAL_CLOCK) &&
+             (framedrop>0 || (framedrop && is->audio_st))) {
+            SDL_LockMutex(is->pictq_mutex);
+            if (is->frame_last_pts != AV_NOPTS_VALUE && *pts) {
+                double clockdiff = get_video_clock(is) - get_master_clock(is);
+                double dpts = av_q2d(is->video_st->time_base) * *pts;
+                double ptsdiff = dpts - is->frame_last_pts;
+                if (fabs(clockdiff) < AV_NOSYNC_THRESHOLD &&
+                     ptsdiff > 0 && ptsdiff < AV_NOSYNC_THRESHOLD &&
+                     clockdiff + ptsdiff < 0) { //TODO: Substract approxiamte time of filter
+                    is->frame_last_dropped_pos = pkt->pos;
+                    is->frame_last_dropped_pts = dpts;
+                    ret = 0;
+                }
+            }
+            SDL_UnlockMutex(is->pictq_mutex);
+        }
 
+        return ret;
     }
     return 0;
 }