EAC3 in MP4 is less common; some versions of MX Player fail to detect EAC3 in MP4 even with custom codec. Remux to MKV:
The “EAC3 audio format not supported in MX Player” error stems from a combination of Dolby licensing requirements and MX Player’s deliberate exclusion of a built-in EAC3 software decoder. This paper has demonstrated that the issue is not a bug but a design choice based on cost and legal constraints. The most practical solution is the installation of a custom FFmpeg codec, which restores EAC3 playback via software decoding. For users unwilling to modify their player, switching to VLC or transcoding the audio track provides viable alternatives. As audio technology evolves toward object-based and immersive formats, media players must adopt modular, licensable decoder frameworks to maintain compatibility without compromising legal compliance. eac3 audio format not supported in mx player