Newbie to Qubes from years of Mint. New installation of QubesOS 4.0.3 and still in confusion mode. When in either the “Work” or a disposable VM and using Thunderbird, I cannot play mp4’s. Most other audio files play fine through firefox. But for mp4’s the video portion will play, but there is no audio. Error message pops up stating, that MPEG-4 AAC decoders not installed and I’m prompted to install them via the repos. Clicking to install the codecs seems to successfully add them to the already-present other two codecs, but still no audio on mp4’s afterward. Next attempt at playing any mp4 by opening them with “Videos (default)” results in the error message “Unable to Play File MP4 decoder is required to play the file, but is not installed”. Online searches have not resulted in a solution so far. How do I proceed from here please. Many thanks.