AVI or MKV with surround sound?

When I download movies in avi, divx or dvdrip or anything it dont play in surround sound. Is this because of the way it was uploaded? Or am I doing something wrong? Ifs its a avi file can i convert it back to dvd and get 5.1 sound? any help would be great. thanks
I have my computer sound going though my stereo. I know i have suround sound, I put a store bought dvd in my compurter and it sounded good.
Thanks
Answer #1
You will not be really able to convert, your system should play them through the speakers though if you set it. Also try and download movies with over 5 channels, not just normal stereo playback.
But i doubt you will be able to convert, to make it 5.1, but your speaker settings must be wrong as it should play if you set up your speakers on your computer right.
Answer #2
EDIT: Comment remove after analyzing my brain fart reply.
Answer #3
How are you supposed to put back what’s not there ?? No can do.
AVIs of around 700MB will normally be MP3 2 chan stereo sound..
Ones around 1400MB that mention AC3 sound will be 5.1..
Answer #4
Nel replied: How are you supposed to put back what's not there ??
Uhhh.. make it up as you go along?

Answer #5
thanks for the replys guys
Answer #6
ffshow can upmix stereo sources to Dolby Pro Logic 2. Use Winamp plugins and do lots of different types of audio manipulation including AC3 encoding if you use an multi channel AC3 decoder.
Answer #7
download movies that are AC3 encoded or DTS.