Can't use Opus Encoder / Copy on MP4

[Osoa]

Trying to copy video and audio from MKV to MP4 using MP4 Muxer, however I get this error when doing so:

It then goes to this error:

Anyone know what to do? Here is the file info:

All help is appreciated.

[eumagga0x2a]

You haven't included the file info (or the broken attachment functionality in this forum prevented it from being shown), but the error message is crystal clear, isn't it? You must re-encode audio to a supported codec (e.g. to AAC by either "AAC (FDK)" or "AAC (lav)" encoder) rather than using copy mode for audio tracks.