Improve h264 in avi hack to also handle duration = number of frames * 2 because maybe field based stuff does this or whatever

Author: myrsloik

src/videosource.cpp

@@ -1101,6 +1101,10 @@ bool BestVideoSource::IndexTrack(const ProgressFunction &Progress) {
             // It's CFR so we know every frame duration is 1 unit
             for (size_t i = 0; i < TrackIndex.Frames.size(); i++)
                 TrackIndex.Frames[i].PTS = i;
+        } else if (VP.Duration == TrackIndex.Frames.size() * 2) {
+            // It's with 99.99% certainty CFR so we almost know every frame duration is 2 units
+            for (size_t i = 0; i < TrackIndex.Frames.size(); i++)
+                TrackIndex.Frames[i].PTS = i * 2;
         }
     }