A few times now, when I have processed Blu-rays from old films where the audio track is mono, in the resulting output mp4 file, I get audio in only the left channel. I haven't figured out how to get audio on both channels. I have tried selecting different audio tracks. The current film I am working on is Bob Dylan: Don't Look Back (1967), Criterion version. Here are some screen captures: https://photos.app.goo.gl/GrVAYv7mM5UCgQJh7 Thanks.