mild decoder adjustment

app/decoder/ffmpeg/ffmpegdecoder.cpp

@@ -211,13 +211,14 @@ FramePtr FFmpegDecoder::Retrieve(const rational &timecode, const rational &lengt
   // Set up seeking loop
   int64_t seek_ts = target_ts;
   int64_t second_ts = qRound(rational(avstream_->time_base).flipped().toDouble());
+  bool got_frame = false;
   bool last_backtrack = false;
 
   // FFmpeg frame retrieve loop
   while (ret >= 0 && frame_->pts != target_ts) {
 
     // If the frame timestamp is too large, we need to seek back a little
-    if (frame_->pts > target_ts || frame_->pts == AV_NOPTS_VALUE) {
+    if (got_frame && (frame_->pts > target_ts || frame_->pts == AV_NOPTS_VALUE)) {
       // If we already tried seeking to 0 though, there's nothing we can do so we error here
       if (last_backtrack) {
         Error(tr("FFmpeg failed to seek to the correct location"));
@@ -238,6 +239,7 @@ FramePtr FFmpegDecoder::Retrieve(const rational &timecode, const rational &lengt
     }
 
     ret = GetFrame();
+    got_frame = true;
   }
 
   // Handle any errors received during the frame retrieve process