Investigate feasibility for back/forward

[maxcurzi]

Ideally, pressing left/right would jump few (say... 5) seconds backward/ahead.

This feature is not trivial because this is not a traditional media player. The video iterator used by opencv probably allows seeking, as well as the audio player (in theory). Due to the independence of A/V streams, a loss of sync is very possible (and not desirable of course)

Investigate if jumping ahead/backward is doable without a major rearchitecture