I’m working on a special purpose plugin that needs up to 64 input channels on the bus it’s inserted in.
In the constructor, I just add one sidechain input and in setPrefereedBussArrangement() I refuse only channel sets larger than 64 channels and otherwise return the value of AudioProcessor::setPreferredBussArrangement().
When I periodically check, getMainBusMaxInputChannels() returns the following values when testing in Reaper:
There were some speaker enums missing in the VST3 wrapper which REAPER tries to use when the channel count is high. I’ve added all the missing enums (and a fallback if REAPER sends us any speaker enums which aren’t defined in the VST3 SDK yet) with commit #643bbdc.
However, even with the above commit, I cannot get more than 24 channels. But debugging the VST3, I see that reaper never even tries to request anything more than 24 channels. It seems to me to be a limitation of REAPER using VST3. Are you sure you have seen other VST3s which support 64 channels in REAPER?
I am absolutely not sure that I have seen this working anywhere.
The plugin will run in a version of Nuendo that has been patched by a third party (not Steinberg themselves) to allow for those channel numbers so it’s a bit hard to test but we’ll definitely give it a go with your fix.