rdk 4.0 demo_vdec_vdis set pal in DM 8148

hi,everyone

I am studing the rdk demo vdec_vdis , I would like to change video display fomat  form ntsc(default) to pal .

I changed the code in demo_vdec_vdis.c

from 

vdisParams.deviceParams[VDIS_DEV_SD].resolution     = VSYS_STD_NTSC; 

to 

vdisParams.deviceParams[VDIS_DEV_SD].resolution     = VSYS_STD_PAL; 

 there is a grey slice in the bottom of the video.

what's the problem ?

I need help...