Youtube only offer audio in either AAC (in a .m4a container) or Opus formats. Since lossy to lossy transcodes always cause some degradation due to the way perc

Youtube only offer audio in either AAC (in a .m4a container) or Opus formats. Since lossy to lossy transcodes always cause some degradation due to the way perceptual codecs discard data, it's always best to use them as-is without converting. AAC is widely compatible these days and is the broadcast industry (ITU / EBU) standard for distribution of end-user audio, the default recording format for most consumer and pro-sumer equipment, and also what Youtube's upload giudelines suggest. Therefore it's better just to get the `-f140 -x` for maximum compatibility, unless you know you can play the Opus audio and have reason to believe the upload was higher quality.