Consider replacing frame slider with input field

[niksirbi]

From @sfmig:

I like the slider option, but an alternative to avoid issues with steps may be to just show the user the total number of frames and let them pick one from 0 to the max number of frames. Maybe something like showing [ ] / 2500, where [ ] is an editable input text box, and by default [ ] is populated with the midpoint of the video. Then we can have buttons for +1, -1, +10, -10 in case that frame is not convenient to quickly switch but stay in the vicinity.

I think something like that would be definitely possible. The only downside is that extracting new arbitrary frames takes time (~2-4 sec). But perhaps users would realise that and avoid needlessly browsing through frames. In other words, the frame viewer is to be used for ROI definition, not as a video viewer.
That said, I like the idea of an input field and the +10 / -10 buttons.