Modify `--single` for 5.3 so MP4 output works just like MKV.
Modify `--single` for 5.3 so MP4 output works just like MKV.

buscarini/video-transcoding-scripts,pefoley2/video-transcoding-scripts,donmelton/video-transcoding-scripts,kaychaks/video-transcoding-scripts,ferrouswheel/video-transcoding-scripts