fixed crash if no audio devices were found

panels/viewer.cpp

@@ -98,8 +98,9 @@ void Viewer::reset_all_audio() {
 }
 
 void Viewer::assert_audio_device() {
-    if (audio_output->format().sampleRate() != seq->audio_frequency
-            || audio_output->format().channelCount() != av_get_channel_layout_nb_channels(seq->audio_layout)) {
+    if (is_audio_device_set() &&
+    		(audio_output->format().sampleRate() != seq->audio_frequency
+    			|| audio_output->format().channelCount() != av_get_channel_layout_nb_channels(seq->audio_layout))) {
 		closeActiveClips(seq, true);
 		init_audio(seq);
     }

playback/audio.cpp

@@ -36,6 +36,10 @@ double audio_ibuffer_timecode = 0;
 
 AudioSenderThread* audio_thread = NULL;
 
+bool is_audio_device_set() {
+	return audio_device_set;
+}
+
 void init_audio(Sequence* s) {
 	stop_audio();
 
@@ -59,14 +63,18 @@ void init_audio(Sequence* s) {
 
 		// connect
 		audio_io_device = audio_output->start();
-		audio_device_set = true;
+		if (audio_io_device == NULL) {
+			dout << "[WARNING] Received NULL audio device. No compatible audio output was found.";
+		} else {
+			audio_device_set = true;
 
-		// start sender thread
-        audio_thread = new AudioSenderThread();
-        QObject::connect(audio_output, SIGNAL(notify()), audio_thread, SLOT(notifyReceiver()));
-        audio_thread->start(QThread::TimeCriticalPriority);
+			// start sender thread
+			audio_thread = new AudioSenderThread();
+			QObject::connect(audio_output, SIGNAL(notify()), audio_thread, SLOT(notifyReceiver()));
+			audio_thread->start(QThread::TimeCriticalPriority);
 
-		clear_audio_ibuffer();
+			clear_audio_ibuffer();
+		}		
     }
 }
 

playback/audio.h

@@ -43,6 +43,8 @@ extern double audio_ibuffer_timecode;
 extern bool audio_scrub;
 void clear_audio_ibuffer();
 
+bool is_audio_device_set();
+
 void init_audio(Sequence *s);
 void stop_audio();
 int get_buffer_offset_from_frame(double framerate, long frame);

ui/viewerwidget.cpp

@@ -399,7 +399,7 @@ GLuint ViewerWidget::compose_sequence(QVector<Clip*>& nests, bool render_audio)
 				case MEDIA_TYPE_FOOTAGE:
 				{
 					Media* m = static_cast<Media*>(c->media);
-                    if (!m->invalid) {
+                    if (!m->invalid && !(c->track >= 0 && !is_audio_device_set())) {
                         if (m->ready) {
                             MediaStream* ms = m->get_stream_from_file_index(c->track < 0, c->media_stream);
                             if (ms != NULL && is_clip_active(c, playhead)) {