MPlayerX frame skip keyboard shortcut

While playing a video in MPlayerX the right and left arrows skip ahead and back 10s respectively. When paused, the right arrow goes ahead 1 frame but the left arrow still goes back 10s.

How do I skip only 1 frame back? Is there some way to assign the left-arrow-while-paused to do this?

Could the "Extra options" in the "advanced" section of the preferences be useful here? is there any documentation on how to use this?

Thanks