Question about RTD VFG7350,Compressed video capture,Mplayer,Cat

I use VFG7350 for capture compressed video and store mpeg files.
The cpu is Intel(R) Celeron(R) M processor 900MHz
The Operating System is Linux Fedora 9 kenerl 2.6.25 2.6.25-14.fc9.i686
I did not modify the board and the OS

firstly,
I use command "cat /dev/video2 > /home/test.mpeg" failed! There is an error:
cat: /dev/video2: Input/output error
and the file test.mpeg is zero bytes.

if i did not use the video2 (compressed ) I use " cat /dev/video0 > /home/testuncompress.avi"
the file testuncompress.avi is not zero Bytes , it is very big. but I use mplayer and can not play the file .

secondly,
I install mplayer.
I use command : "mplayer -dumpstream -dumfile /dev/video2 test.mpeg". the command immediately finished and the file is zero bytes.
if i use video0 , the file is nozero bytes. but can not be played by Mplayer.

infact the module such saa7134, saa7134_compress,saa6752,i2c and so on are all existed and can be displayed by command lsmod. And the driver saa7134, V4l2 and i2c are all right.

how to capture the compressed video???