The audio doesn't match up with the video when using Convert AVI to MP4.
This problem could be caused by various causes:
The codecs you use are not working as they should, therefore an alternative is required. I recommend removing the old ones and then install Combined Community Codec Pack. I have used this package and it was working just fine.
The original file has the audio and video desynced. Try adjusting the FPS rate. Lower it if it's close to 30. This should fix the issue as well.