Wishlist: Navigate between keyframes only

[pjotrek-b]

When analyzing lossy-encoded material, I often find it handy to have the possibility to navigate on keyframes (I-frames) only.

This would also make it easier and more comfortable to analyze I-P-B frames (as requested in #94), since you jump to a keyframe and then navigate left/right from there. I use it like this in VirtualDub all the time.

The keyboard shortcut for this in VirtualDub is:

Shft+Left: Prev keyframe Shft+Right: Next keyframe