We should also at least consider not only supporting rendering pattern channels into separate buffers, but also rendering individual instruments into separate buffers. (suggested by Bombe on IRC)

Wanted to add that this feature would be very much welcomed and would add additional value to the base library. A lot of us old school users are visualization nerds, especially when it comes to mod files :)

This would be very welcome. My particular use-case is I would like to use libopenmpt to render mods in realtime and be able to mix the channels separately in a live setting. What I would ultimately like is to integrate libopenmpt and Pure Data https://puredata.info so that libopenmpt renders the audio into X channels and then these come into Pure Data for further processing and manipulation. Both audio and event data could be brought in.

I would also want this, to show visualizations in my player, BZR Player 2.

From https://forum.openmpt.org/index.php?topic=7251:
In addition to forcing a somewhat slower rendering path (because we currently render and mix a channel at the same time, if no plugins are involved, using separate buffers will significantly increase cache pressure and hurt older systems), the most difficult thing is designing the API, for the reasons outlined in the issue: channels can be grouped and routed through plugins, so the waveform per channel will not be what is finally be heard from that channel, and the waveform per-plugin might contain multiple channels. It's also difficult to design the API somewhat future prove regarding even more complex audio routing graphs which might get added sometime.