VST- Multi in/out plugs (IOChanged)

Hi, What is the correct way for a VST plugin to notify Reaper it would like to change it's input/output configuration. From looking in the VST 2.4 docs, I understand I should - Call "IOChanged": [returns FALSE] - Host can not accept input/output changes. - Do not do anything, Exit. [returns TRUE] - Change the number of inputs/outputs in the AEffect structure. - Call "IOChanged" again to notify the host that something has changed. However from what I can tell, Reaper always returns false to IOChanged. If a plugin goes ahead and changes the input/output count regardless, Reaper also seems to accept it. kind regards, Shannon (Developer of Poise Percussion Sampler. )

Reaper tries to be pretty flexible about things like this. It actually ignores the IOChanged call, but checks the plugin's AEffect::numInputs and numOutputs on every buffer block. So as far as Reaper is concerned, as long as you're not changing some storage in the middle of processing samples, you should be fine just changing the AEffect.

"You can almost always get the host name with audioMasterGetVendorString or audioMasterGetProductString. " Thanks. Reaper is good here, but some hosts aren't so much. I'll have a go at adding a work-around if Reaper is detected as the host. I'm guessing your not a Reaper developer Schwa?

You guess wrong!

hehe.. Fair enough. :) Well if your not disclosing any trade secrets I'm still curious why Reaper ignores the "IOChanged"? I'm still a bit of a novice when it comes to the VST spec. (I've started writing some VST hosting code but it's still at a very alpha stage).

Because VST is so poorly specified, we try to implement as little as possible of it and just react dynamically to any changes. Any time you make an assumption about what plugins expect it seems to break half of them. Having said that, it looks like we can just always return 1 from audioMasterIOChanged. But if that breaks somebody else's plugin, we're sending them to your house.

Ok cool, that sounds like fair reasoning. "Having said that, it looks like we can just always return 1 from audioMasterIOChanged. But if that breaks somebody else's plugin, we're sending them to your house." Hehe. :) Thanks for your help Schwa.

In my code to change the number of outputs, I've added a check to see if Reaper is the host (audioMasterGetProductString), if so my function goes ahead ignoring the "IOChanged" result. It seems to work so far. Thanks.