Directshow capture graph captures only one image in .avi

[dvd_]

I've built a simple capture graph to capture video from a usb cap device.

The graph is: Cap filter -> AviMux -> File Writer

The problem is that the .avi file that is recorded displays only the first image being captured and not the whole video stream.
(played in windows media player)

I've tried to set the AVI compatibility index via the AviMux filter to both true and false, and it didn't help.

When I insert an encoder filter to the graph:
Cap filter -> Encoder -> AviMux -> File Writer
the video is recorded fine.

Any ideas?
For my specific task i need to be able to record without an encoder filter.

Thanks

[ChiDragon]

Possibly WMP doesn't have a proper filter to decode the uncompressed video. Try opening it in VirtualDub.