fixing audio sync without changing the video/audio quality of mp4 video

[aruwin]

Hello!
I want to fix an audio sync problem of an mp4 video without losing its quality. I tried using avidemux but after fixing it I couldn't play the video. I also tried with virtualdubmod but that software doesn't load anything else besides avi files. Anyone knows how to fix this? Or perhaps a better freeware?

[hech54]

If it opens in AviDemux, it can be fixed(synced) and output to the same exact file with no quality loss.
COPY
COPY
MP4

[poisondeathray]

If it's just a shift ie. a constant + or - ms delay - other options are mymp4boxgui, yamb (both GUI's for mp4 box)

[aruwin]

If it opens in AviDemux, it can be fixed(synced) and output to the same exact file with no quality loss.
COPY
COPY
MP4

Thanks! It worked when I changed the output to MP4