Adding MP3 to Video

[atkinson40]

I have a Tai Chi MP4 video in the format where it will play on my Kindle Fire 7.  I have an audio  narration of the moves in MP3 format that is time synched to the movie that I play on my MP3 player/headphones as I'm doing the moves.  I'd like to also add the MP3 to the MP4, but in doing so they become out of synch, somehow the audio lags the video. 

What should my output settings be in Avidemux?  I would like to keep the kindle format and just add the MP3.

Thanks Kevin

[zakk]

use mp4v2 or mp4 container. if this doesn't work, try to re-encode the sound.