feat: cross-fade jump cuts

[WofWca]

This is a pretty big one, sounds hard to implement.

You might have watched some videos that use this effect. It's where there is a jump cut, but not a regular one when one clip is immediately replaced by another one, but where you can hear the very ending of the first sentence and the very start of the next one (like 0.2 seconds) at the same time. This is sort of like setting "margin" to a negative value.

I believe with this effect we can save some more time, or improve clarity of audio.

[t9999clint]

I would like a very similar feature actually, just not for audio.
When skipping segments it would look a lot better to have a 3-5 frame video crossfade between the segments that are being stitched together. This makes the video a lot less jarring when watching people moving around. I used to do this a lot manually when editing videos for people. It makes a big difference and would be pretty neat to have a extension kinda do this automatically for the twitch VODs I like to watch.
I have no idea if that's even possible to implement. Maybe even a quick and dirty method of grabbing the first frame of the next segment and just overlay it at increasing opacity over the video feed right before it skips to the next segment.

On the audio side...
A cross fade thing I would like would be for the audio to fade to silence right before the jump and then fade back in to normal volume right after. This would also be super nice for the non skipping, fast forward mode. When there's background music it starts to sound super weird when it's fast forwarded and is kinda distracting.
This in theory should be pretty simple to implement. (I'm not really a programmer, so I might just be talking out my ass here)