Add Avisynth support to FFMPEG

I am working on a few pipelines where I’m inevitably rendering a video twice due to ffmpeg 7.1 in Video AI not including the --enable-avisynth flag. I would love to be able to feed the avs conversions directly into this build.

I have tried a few different techniques to try and pipe between two ffmpeg versions, but they don’t handshake nicely in any way.

Can we have this considered in a future update?

https://www.ffmpeg.org/general.html#AviSynth