When i play a MP4 video with AAC audio VLC says:
[00000375] main decoder error: no suitable decoder module for fourcc `mp4a'.
VLC probably does not support this sound or video format.
If i open the file with amarok i can hear the audio perfectly and in Windows with the same version of VLC and the same MP4s i have no problems.
my system is Fedora Core 6 x86_64 with linux kernel 2.6.19-1.2895.fc6
VLC version 0.86a