Avisynth problem with VirtualDub

I used DirectShowSource as the script to open mp4 with AAC audio. VirtualDub can open it and show that both video and audio stream exist. My problems are:
- VirtualDub freezes when it tries to play the clip.
- The output clip has video but no audio.

If I work with an avi file with mp3 track, DirectShowSource works as expected.

Any ideas?