The advice did not help.
I went to control center, added as repositories "Tainted updates (distrib 3)" and "Tainted 32bit updates (distrib 6)," and added about as many of the other repositories as the system would allow, searched for the term mp4, and installed every repository program whose name remotely suggested it had anything to do with audio. Then I updated everything.
Then I went looking for anything that included the letters mpeg, which is what my error message on the Video player program said it was missing so it could not play the audio portion on a *.mp4. Then I installed all of those programs and updated them too.
I also installed a new vlc from tainted.
All told, about an hour and a half, and about 1.5 gigabytes downloaded and about 1 full gigabyte of hard drive space newly occupied. I rebooted a couple of times along the way.
Then still nothing. Stone silence on my downloaded videos.
When I tried playing an *.mp4 downloaded youtube video using "Videos," the from-the-box player, the error message I get is I am missing an MPEG-AA4 decoder plug-in, which I was then prompted to search for. A long, long first search ended in a hang. Then a long, long second search (I wish I knew where it was searching) yielded no message or sound, just a blank spot where an error message probably should have been, a gray box but without a message, so I assume it was a different kind of crash. When I subsequently tried an *.flv on Video, I again got no sound and the blank box but no prompt for a search.
I later rebooted, retried my *.mp4, and searched again.
Could not find plug-in in any configured software source.
Then I tried my *.flv, and got no error message or sound.
The error message from the new tainted VLC for both the *.mp4 and the *.flv videos was,
No suitable decoder module: VLC does not support the audio or video format "mp4a". Unfortunately there is no way for you to fix this.
With Dragon Player, no error message or sound with either *.mp4 or *.flv.
I know my audio card works because I can hear streaming youtubes just fine, and I have plenty of system sounds.
Please advise if I am doing something wrong, or if I need a different player, or if Mageia simply doesn't have the capacity to play audio on stored files.
Thanks.