Yup. MKV and avi are containers. MPEG on the other hand is a compression standard. Of course you may have various codecs further. I too am not clear about the. Question. You will find many video files that have 5.1 channel sound.
Hi
Yes you can convert .mkv files with AAC 5 channel audio to AC3 5.1 channel.
You can use popcorn audio converter to do that.
It works great.
PM me in case you need more information.
Even I am not sure about the question, but if AAC 5.1 to AC3 5.1 is what the OP wants I can vouch for popcorn, which I have used for the same purpose. following thread has my tiny DIY guide on how to use popcorn and convert AAC to AC3 5.1 .....
It is a graphic front end to ffmpeg. It is the first video converter that doesn't seem to require knowledge of paramaters that the occasional video dabbler such as myself might find utterly incomprehensible. Basically, you tell it want you want to do with the resultant video, and it sets the ffmpeg command line appropriately and runs it.
For anyone who may not understand the various abbreviations in a thread such as this, it is well worth a look. Those who do speak the language will find that it can be fine-tuned too.
I only discovered it last week, and have used it but once, but, especiaally considering the input file format (avhcd) was entirely new to me, it was my most painless experience of video conversion yet.