I can't think from the top of my head about what program you can use because *.avi is usually converted to *.wmv. This means that *.wmv is a format that compresses the *.avi to make the file size smaller, and you ususally lost video quality and audio as a result in most cases.
If you convert *.wmv to *.avi, you will still get the same video and audio quality from the *.wmv file only just a larger size, perhaps.
What are you trying to do exactly, maybe I can try and help.
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