MP4 file I create is silent in Quicktime, OK in VLC; unless remuxed. why?

[blueseth]

I'm working on MP4 muxing software that takes input from a hardware H.264 encoder and AAC-LC encoder. The file I produce plays OK in VLC, but audio is silent in Quicktime or when loading into Sony Vegas. If I "convert" the file through VLC to another .mp4, or use Handbrake to convert it, then audio works in Quicktime or Vegas from the resulting file.

Here is an example file I produced (8MB, 5 sec) which demonstrates the problem. http://www.filedropper.com/shortrdfrecwithaudio_1

I'm picking through mp4 box headers at the moment playing spot-the-difference but not coming up with much.
Any clues on debugging this, useful analysis utilities etc, would be welcome.

[bat999]

I'm picking through mp4 box headers at the moment

Hi
MP4Box isn't perfect.
m4a files muxed with MP4Box don't play on some iPods and some other hardware players.
Maybe Quicktime doesn't like MP4Box either.

Try muxing your h264/aac with a different muxer such as mp4creator to pin it down.

[blueseth]

I'm not using the "MP4Box" utility. This is my own from-scratch muxing software. Seems I'm getting something wrong with the formatting.