DVD Ripper mp4 output file resolution by ripping dvd

[coolala]

This is more a question than an issue. When I have dvdfab ripped a DVD, by default the mp4 output file resolution is 856x480. Even though I change it to 854x480, the output file resolution would be automatically changed to 856x480. If I go into the edit, crop, it specifically says that width:854 and Height: 480. With the 2x480 pixels difference it isn't a big deal but I'm curious why this is designed in this? Thanks.

[coolala]

forget it... the resolution is set to be multiple of 8, right? Typically on Internet the resolution recommendation is 854x480 which triggered my curiosity.