cccombiner: don't drop buffers on video timestamp discontinuities

If we receive video buffers with non-perfect timestamps, the
caption buffers' timestamps might fall in the interval between
the end of one video buffer and the start of the next one.

Make our criteria for dropping that the caption buffer has
a timestamp older than the end of the previous video buffer,
not older than the start of the new one, unless of course
this is the first video buffer.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1207>

diff --git a/ext/closedcaption/gstcccombiner.c b/ext/closedcaption/gstcccombiner.c
index a8adb78..fbcf865 100644 (file)
--- a/ext/closedcaption/gstcccombiner.c
+++ b/ext/closedcaption/gstcccombiner.c
@@ -175,8 +175,17 @@ gst_cc_combiner_collect_captions (GstCCCombiner * self, gboolean timeout)
     if (caption_time >= self->current_video_running_time_end) {
       gst_buffer_unref (caption_buf);
       break;
+    } else if (GST_CLOCK_TIME_IS_VALID (self->previous_video_running_time_end)) {
+      if (caption_time < self->previous_video_running_time_end) {
+        GST_WARNING_OBJECT (self,
+            "Caption buffer before end of last video frame, dropping");
+
+        gst_aggregator_pad_drop_buffer (caption_pad);
+        gst_buffer_unref (caption_buf);
+        continue;
+      }
     } else if (caption_time < self->current_video_running_time) {
-      GST_DEBUG_OBJECT (self,
+      GST_WARNING_OBJECT (self,
           "Caption buffer before current video frame, dropping");
 
       gst_aggregator_pad_drop_buffer (caption_pad);
@@ -359,6 +368,8 @@ gst_cc_combiner_aggregate (GstAggregator * aggregator, gboolean timeout)
     flow_ret = GST_FLOW_OK;
   } else {
     gst_buffer_replace (&self->current_video_buffer, NULL);
+    self->previous_video_running_time_end =
+        self->current_video_running_time_end;
     self->current_video_running_time = self->current_video_running_time_end =
         GST_CLOCK_TIME_NONE;
   }
@@ -419,7 +430,7 @@ gst_cc_combiner_stop (GstAggregator * aggregator)
 
   self->video_fps_n = self->video_fps_d = 0;
   self->current_video_running_time = self->current_video_running_time_end =
-      GST_CLOCK_TIME_NONE;
+      self->previous_video_running_time_end = GST_CLOCK_TIME_NONE;
   gst_buffer_replace (&self->current_video_buffer, NULL);
 
   g_array_set_size (self->current_frame_captions, 0);
@@ -436,7 +447,7 @@ gst_cc_combiner_flush (GstAggregator * aggregator)
       GST_AGGREGATOR_PAD (GST_AGGREGATOR_SRC_PAD (aggregator));
 
   self->current_video_running_time = self->current_video_running_time_end =
-      GST_CLOCK_TIME_NONE;
+      self->previous_video_running_time_end = GST_CLOCK_TIME_NONE;
   gst_buffer_replace (&self->current_video_buffer, NULL);
 
   g_array_set_size (self->current_frame_captions, 0);
@@ -630,7 +641,7 @@ gst_cc_combiner_init (GstCCCombiner * self)
       (GDestroyNotify) caption_data_clear);
 
   self->current_video_running_time = self->current_video_running_time_end =
-      GST_CLOCK_TIME_NONE;
+      self->previous_video_running_time_end = GST_CLOCK_TIME_NONE;
 
   self->current_caption_type = GST_VIDEO_CAPTION_TYPE_UNKNOWN;
 }

diff --git a/ext/closedcaption/gstcccombiner.h b/ext/closedcaption/gstcccombiner.h
index df3dff0..93f3d85 100644 (file)
--- a/ext/closedcaption/gstcccombiner.h
+++ b/ext/closedcaption/gstcccombiner.h
@@ -45,6 +45,7 @@ struct _GstCCCombiner
   GstAggregator parent;
 
   gint video_fps_n, video_fps_d;
+  GstClockTime previous_video_running_time_end;
   GstClockTime current_video_running_time;
   GstClockTime current_video_running_time_end;
   GstBuffer *current_video_buffer;