What do you mean by AC3 files? Are they just the audio part separated from video DVDs or something else? What is the file extension and container type and how the files are made?
You're right, they are the audio portion of DVD-Videos. The file extension is actually "ac3". They are pretty simple to make using any of the standard DVD rippers to demux the streams.
This results in a single 5.1 "ac3" file that plays back in my old WinAmp 2.8 install with the AC3 plug-in. If I send the bitstream directly to my SPDIF output, my receiver correctly interprets the file as "Dolby Digital 5.1".
I have been able to play AC3 and DTS videos with MC a long time. I have used AC3Filter for audio decoding or direct digital pass-through to a separate DD/DTS decoder. If the AC3 files are audio only the solution could be to put them in AVI containers.
I've never successfully used MC to playback video material, be they AVIs or DVDs (either ripped or on the disc). Of course, I've been satisfied with my other tools to deal with video, so I haven't put much effort into making MC work for me.
However, you propose an interesting work-around. How would I go about transforming my audio-only AC3 file into an AVI?
Best,
brad