The video frames captured by VIN port are not the same

Our processor is DRA74X, with 3.02.00.03 SDK version.

I'm using vin4b port to capture BT656(NTSC-M) 8-bit video signal from adv7182a subdevice. The video source keep providing the same pattern(color bar). I use below command to capture the video, 

yavta -c1 -fUYVY -Fvout_720x480_UYVY.yuv -s720x480 /dev/video1 

here are my questions,

1. The size of the video frame i captured is 691200, which mean the resolution is 1440 x 480, but the video source provide 720 x 480, and my captured command also specify the size is 720 x 480, why the system generate video frame with 691200 size?

2.Each time the valid data size is different(valid data mean it is the YUV data of color bar, otherwise, the data is 0x00). Sometimes the valid data size is 349920(which mean, 720 x 486), sometimes is 365760(which mean, 720 x 508), sometimes i even got a full size of valid data(which mean i got 691200 valid data, 720 x 960), why?

Regards,

Shawn