No 7.1 return from winamp plugin in ffdshow since klMega 11.1

Up till & including version 11.00 of the Kazaalite Mega codec pack, I was able to use two plugins for Winamp in ffdshow to upmix sound from 2.0 or 5.1 channels to 7.1 audio. Within ffdshow, I did first have to use the mixer filter before the Winamp filter to set the number of output channels to 7.1, so the additionally returned channels from the winamp plugin would be accepted by ffdshow and made audible. In versions 11.10 and 11.20 of the Mega codec pack, the side and rear speakers no longer get any signal when using the 5.1 to 7.1. upmix plugin. (Mysteriously, the other upmix plugin 2.0 to 7.1 does still render sound over all 7.1 speakers. So there is some difference between them, method of channel numbering maybe.) The Kl Mega codec pack 11.10 and 11.20 versions appear to use the same ffdshow try-out (4533, but with later dates, the one from February 11 2015 still worked trouble-free).

When I first discovered the problem, I had initially hoped to solve it by installing an older version of ffdshow prior to installing a newer codec pack, but during installation of the pack the installer insists any old versions of ffdshow be removed.

I understand it might be hard for anyone else who doesn't have the same winamp plugin to exactly duplicate my set up, but has anything changed this spring in ffdshow audio that might cause problems accepting 7.1 winamp output? I'm not willing to give up on 5.1 to 7.1 upmixing, since it sounds really great. Which as things stand, would mean that I couldn't update my codecs.

LAV Audio Decoder now uses the side channels by default instead of the rear channels. It seems that your Winamp plugins don't support that layout. You can use the "swap channels" filter in ffdshow to swap the side channels back to the rear.

Alternatively, you could create two presets (one for 2.0 input and one for 5.1) and then create a custom mixing matrix. Then you don't need to use any plugins, and you can specify exactly how mixing should be performed. Only complex thing is to figure out the correct mixing coefficients. For example for 2.0 > 7.1, you take 0.7071 of left and right for the center. 0.5 of left and right for the back/side channels.

Ah, yes thank you! Indeed, LAV proved to be the rascal. I'm rescued.

What I love about the winamp plugin, is that a VST bridge exists for Winamp which allows you to use all kinds of professional sound processing plugins in the VST (Steinberg) format. For that reason, it would be great if the winamp plugin would also work in the 64 bit version of ffdshow, but in 64bit I just get 5.1 channels when I try to use the 7.1 upmix plugin and the side speakers remain silent.

Perhaps the winamp plugin is entirely ignored in 64bit ffdshow because winamp and plugins are 32bit? I noticed that when I tick the 'allow multichannel audio processing' box in the winamp filter of 64bit ffdshow, then close the filter gui and open it again, the box is no longer ticked.

64bit version requires 64bit plugins.