If audio is not supported on some of your MP4 (.mp4) files, it's probably because the soundtrack is encoded in DTS. However, the specifications of the mp4 (container) protocol do not support DTS audio encoding. Even if in practice, it is possible to force the integration of a DTS track in an MP4 container, the audio will not be able to work on all the players respecting the MP4 protocol to the letter as is the case in hardware decoding. with Zappiti players because in hardware decoding, the DTS license imposes these restrictions.To solve this problem, there are solutions:
1. You can play this type of files using VLC (My Apps / Aptoide TV / VLC).
2. You can convert this kind of file to MKV using MKVToolNix software.