MMA can only play files that are natively supported by your device. MMW can Auto-Convert unsupported files to a format that your device does support.

With video files this can get tricky as the extension may be supported, but the video or audio part may not.

what device and version of mma are you using? I play mp4 on my Samsung G8

mmAndroid syncs a video playlist I have from mmWin
But, mmA doesn't play them, they just seem frozen
The *.mp4 files play fine from the DIR on VLC

Any ideas?
Thanks