The files need to be made using a small list of codecs, both for audio and video. Use mediainfo program to see all of a files specifics.
For audio stick with AAC for stereo or AC3 for multitrack (or stereo).
For video stick with h.264.
There are more, but I find that sticking with these couple, easy to remember, codecs works well.
"I might be moving to Montana soon..."
FZ