[SOLVED] MeGUI 'Unable to render the file'

[GG-Xtreme]

(Trying to keep separate issues in separate threads.)

I have a set of .mkv's with H.264 video and AC3 audio, and I wanted to re-encode the audio to AAC so I could play them on my Android phone. However, after much experimentation with remuxing, I've come to the conclusion that these files use VFR because I *cannot* get the video and audio to sync either by simply replacing the audio with MKVmergeGUI (syncs fine on computer, way out of sync on phone) or by putting the H.264 stream into a new container using any MP4Box settings (doesn't sync on either computer or phone, video length is wrong).

I assumed I could get around this using convertFPS in AviSynth through MeGUI, but it seems I can't even load the original .mkv's into MeGUI without "Direct Show Error: Unable to render the file. You probably don't have the correct filters installed". I've tried reinstalling AviSynth, MeGUI and ffdshow in different orders, and the files play fine in MPC using both the internal filters and ffdshow.

Can someone help me with this issue? Or possibly suggest another method of converting VFR to CFR?

Edit: BTW, I'm running Windows 7 Ultimate 64-bit. I'm using 64-bit ffdshow and AviSynth (as well as MPC).