midi commands are forwarded to your system, you'd have to
capture them at a later point.

I'm not sure I follow you here. Would you please elaborate some more? How exactly do I 'capture them at a later point'?

The midi data is just (sort of) sent to the midi device of your operating
system, like the midi mapper/wavetable synth in windows. You'd need
a program that can intercept and record those messages, don't know
if something free exists.
As the midi data doesn't go through the regular sound emulation of
dosbox, midi music can't be recorded with the avi capturing of dosbox.

Ah I see. Thank you. I've switched to soundblaster for music and recording is fine.

It's just that midi can sound better depending on the game and the
capabilities of your os midi drivers/soundcard. But nice that switching
to soundblaster works for you 😀

dosbox captures midi as well with some combo.
doesn't work with all games perfectly yet though.

But it isn't added to avis, you'd have to render the midi file into .wav
and merge it with the existing sound.

yes that is correct.

Maybe the game can be configured do do FM synth instead of midi?

Hm guess that's what they're doing when switched to soundblaster
for music, but don't know.

Has anybody considered making use of the host OS recording sources "What U Hear" or "Midi Synth" for recording audio when capturing to video?

For example, if the game uses MIDI music, and the user starts recording video, have DOSBox automatically record the soundcard's MIDI synth output and mix it with the emulated digital sound for the final file. Granted this would add a bit to the CPU usage when recording video, but at least you'd keep the users happy and less time spent dealing with their complaints means more time for the devs to write code.