Unsupported audio codec error when remuxing mkv to mp4 (2.7.5)

[eumagga0x2a]

Avidemux doesn't support soft subtitles, it can only hardcode them using the libass-based video filter. If you need to mux a subtitle track into mp4, it makes more sense to use ffmpeg.

[gekemo]

In that case I should probably mux individually since the files all have different sub files then. Hardcoding is fine actually, because for whatever reason my bluray player doesn't recognise the sub files.
Thank you for all your help!