ADV7481 output image is stretched

hi,

The adv7481 is used to convert HDMI IN data to CSI data. there is a issue about the HDMI in with size 720x576 from DV device, the output image after ADV7481 is stretched, for example, the cricle in the scene is outputed to be a oval. 

I cannot find such function that adv7481 could do the streched things, but actually it really does, and we also checked the DV device, it's okay if we connect the DV to PC displayer or some other HDMI IN supported devices.

so, how to make the shape okay as original?