Fix the display of storyboards and videos when the segment is long

[jbilcke-hf]

Context

In one picture: the storyboard is cropped, and the video is stretched.. both should be considered like a bug.

Solution

If we look at legacy video editors they tend to solve this issue that way, by repeating the frames:

[jbilcke-hf]

made some improvements, still this improved version is improvable.