Merge audio from one file with video from another file

Hello,

I have an HD movie with bad sound in one file.
And I have a low-res movie with good sound in another file.

Id like to merge these two, using the HD video and good sound, into one file.

One file is .MKV (video codec h264) and the other is .AVI (video codec MPEG4 MP50).

I tried Virtualdub but it doesnt support .MKV files.

Any help is really appreciated. Thanks.

Edit: I was able to extract the good sound from the .AVI file in .WAV format.
Now I need to replace the bad sound in the .MKV file with the .WAV file...

 

MKVMergeGui (part of MKVToolnix).

Load/drag the mkv file in and deselect the audio.
Load/drag the wav in and 'Start Muxing' to merge.
(optionally, drag the AVI in instead of the wav and deselect it's video)
http://www.videohelp.com/tools/MKVtoolnix

 

Thanks very much.

Audio ended up half a second early than the video, but I'll figure out how to sync it.

 

Highlight video, then select tab for 'Format specific options' then insert a value in the box labeled 'Delay(in ms)'

FYI if you playback the video in 'Media Player Classic', you can adjust the delay using the + or - keys and the value will be displayed.
You can insert that value in the box.

 

Thanks again.