How to grab fast/low quality frames

[Tengyyy]

I'm building a local video player and I'm currently trying to create the feature similar to youtube where it shows little preview frames when hovering on the seekbar/slider at the bottom of the screen. However its currently very heavy on the cpu and lags noticeably with higher resolution videos. Is there a way to grab lower quality frames or decrease the resolution or bitrate to make the feature more efficient? (I already tried setVideoOption("preset", "ultrafast"), but it didn't have any noticeable impact.)

[saudet]

A feature like that is probably only decoding key frames, and not using a precise seeking function, so don't try to use that.