2 Suggestions - configurable offset and forwards+backwards mode

[whydna]

Would be awesome to be able to configure offset until the video starts playing (i.e allow video to get into view first, and then start playing).

Also, would be cool to have a forwards+backwards/pingpong mode so the video plays forwards, and as you continue scrolling it plays backwards returning to the original position as it leaves the screen.

[gegray]

I have something similar working, will get the fork up soon but I've made lots of changes.