viewer: improved frame queuing

app/codec/ffmpeg/ffmpegdecoder.cpp

@@ -145,6 +145,10 @@ bool FFmpegDecoder::OpenInternal()
 TexturePtr FFmpegDecoder::RetrieveVideoInternal(Renderer *renderer, const rational &timecode, const RetrieveVideoParams &params, const QAtomicInt *cancelled)
 {
   if (AVFramePtr f = RetrieveFrame(timecode, cancelled)) {
+    if (cancelled && *cancelled) {
+      return nullptr;
+    }
+
     if (InitScaler(f.get(), params)) {
       VideoParams vp(instance_.avstream()->codecpar->width,
                      instance_.avstream()->codecpar->height,
@@ -790,6 +794,10 @@ AVFramePtr FFmpegDecoder::RetrieveFrame(const rational& time, const QAtomicInt *
     // Pull from the decoder
     ret = instance_.GetFrame(working_packet_, filtered.get());
 
+    if (cancelled && *cancelled) {
+      break;
+    }
+
     // Handle any errors that aren't EOF (EOF is handled later on)
     if (ret < 0 && ret != AVERROR_EOF) {
       qCritical() << "Failed to retrieve frame:" << ret;