{audio,video}decoder: Forward SEGMENT_DONE events immediately and drain decoders

Otherwise we're going to wait with draining until the next data comes, which
is a bit suboptimal and might take a long time... or maybe never happens.

gst-libs/gst/audio/gstaudiodecoder.c

@@ -2156,6 +2156,18 @@ gst_audio_decoder_sink_eventfunc (GstAudioDecoder * dec, GstEvent * event)
       ret = gst_audio_decoder_push_event (dec, event);
       break;
 
+    case GST_EVENT_SEGMENT_DONE:
+      GST_AUDIO_DECODER_STREAM_LOCK (dec);
+      gst_audio_decoder_drain (dec);
+      GST_AUDIO_DECODER_STREAM_UNLOCK (dec);
+
+      /* Forward SEGMENT_DONE because no buffer or serialized event might come after
+       * SEGMENT_DONE and nothing could trigger another _finish_frame() call. */
+      if (dec->priv->pending_events)
+        send_pending_events (dec);
+      ret = gst_audio_decoder_push_event (dec, event);
+      break;
+
     case GST_EVENT_EOS:
       GST_AUDIO_DECODER_STREAM_LOCK (dec);
       gst_audio_decoder_drain (dec);

gst-libs/gst/video/gstvideodecoder.c

@@ -1071,6 +1071,25 @@ gst_video_decoder_sink_event_default (GstVideoDecoder * decoder,
       event = NULL;
       break;
     }
+    case GST_EVENT_SEGMENT_DONE:
+    {
+      GstFlowReturn flow_ret = GST_FLOW_OK;
+
+      flow_ret = gst_video_decoder_drain_out (decoder, TRUE);
+      ret = (flow_ret == GST_FLOW_OK);
+
+      /* Forward SEGMENT_DONE immediately. This is required
+       * because no buffer or serialized event might come
+       * after SEGMENT_DONE and nothing could trigger another
+       * _finish_frame() call.
+       *
+       * The subclass can override this behaviour by overriding
+       * the ::sink_event() vfunc and not chaining up to the
+       * parent class' ::sink_event() until a later time.
+       */
+      forward_immediate = TRUE;
+      break;
+    }
     case GST_EVENT_EOS:
     {
       GstFlowReturn flow_ret = GST_FLOW_OK;