Timing Postproc keyframe snapping should use ms instead of frames

[nielsm]

Specifying the snap distances for keyframe snapping in the Timing Postprocessor in frames rather than milliseconds might not be a good idea, especially if considering the case of VFR.
The need for keyframe snapping is to minimise the visual problem of subs blinking on/off close to a scene change, but "close" should be defined in playback time, which can vary a lot depending on the frame rate of the video. With VFR video the frames around different scene changes can have varying lengths, meaning the snapping will be visually uneven.

[TheFluff]

I will take a look at doing this, but it'll have to wait until after the strings thaw/feature thaw.

[FichteFoll]

What about using both, frames and time, to specify the snapping range? I can imagine cases when just resnapping to keyframes that are 1 or max 2 frames async would be useful. Furthermore, this does not involve new code since snapping to frames is already possible.

[tophf]

It would be a indeed an extremely useful feature!
Time-Shift has this capability like forever.

[Plorkyeran]

Done in r6311.