Passthrough Video and convert Audio

[Teoulis-69]

Hi, i'm trying to convert an audio stream in an mp4 (h264/avc) video file. The audio stream originaly is in mp3 format and i wish to convert it to AAC or AC3 format without re-encoding the video. I found an old thread in the forum about this question but it was back in 2005 and wasn't very helpfull. So i was wondering if there is a new way to do so.
Note 1 : I already tried SUPER � v2011.build.49 but the audio was with a lot of distortion.
Note 2 : I also tried DVDfab v8 video converter but it re-encodes the video.

[Baldrick]

avidemux, open mp4, under video change to copy, under audio change too aac or ac3, under format change to mp4, save as mp4.

xmedia recode, open mp4, under profile change to custom, under format change to mp4, under the video tab choose video copy, under the audio tab change too aac, add job, encode.

[Megalev]

Thanks for this now old, thorough advice.