Timestamp audio emissions from butler and hence discard very late

audio in FilmViewer.  This should help with the case where lots
of video frames are rapidly discarded when they are late but the
corresponding audio is not, hence audio buffers get overfilled.

2 files changed, 19 insertions, 1 deletions

diff --git a/src/wx/film_viewer.cc b/src/wx/film_viewer.cc
index ef28018e9..ce34b06b7 100644
--- a/src/wx/film_viewer.cc
+++ b/src/wx/film_viewer.cc
@@ -882,6 +882,16 @@ FilmViewer::config_changed (Config::Property p)
 }
 
 DCPTime
+FilmViewer::uncorrected_time () const
+{
+	if (_audio.isStreamRunning ()) {
+		return DCPTime::from_seconds (const_cast<RtAudio*>(&_audio)->getStreamTime());
+	}
+
+	return _video_position;
+}
+
+DCPTime
 FilmViewer::time () const
 {
 	if (_audio.isStreamRunning ()) {
@@ -895,7 +905,14 @@ FilmViewer::time () const
 int
 FilmViewer::audio_callback (void* out_p, unsigned int frames)
 {
-	_butler->get_audio (reinterpret_cast<float*> (out_p), frames);
+	while (true) {
+		optional<DCPTime> t = _butler->get_audio (reinterpret_cast<float*> (out_p), frames);
+		if (!t || DCPTime(uncorrected_time() - *t) < one_video_frame()) {
+			/* There was an underrun or this audio is on time; carry on */
+			break;
+		}
+		/* The audio we just got was (very) late; drop it and get some more. */
+	}
 
         boost::mutex::scoped_lock lm (_latency_history_mutex, boost::try_to_lock);
         if (lm) {
diff --git a/src/wx/film_viewer.h b/src/wx/film_viewer.h
index e4449fa2f..a41500ace 100644
--- a/src/wx/film_viewer.h
+++ b/src/wx/film_viewer.h
@@ -114,6 +114,7 @@ private:
 	void recreate_butler ();
 	void config_changed (Config::Property);
 	DCPTime time () const;
+	DCPTime uncorrected_time () const;
 	Frame average_latency () const;
 	DCPTime one_video_frame () const;