What does HackerNews think of lossless-cut?
The swiss army knife of lossless video/audio editing
Try this: https://github.com/mifi/lossless-cut
I am using the binary on macOS. The UI is a bit idiosyncratic but it works quite well and is ideal to cut a video down to the essential parts without loss of quality.
My startup is using ffmpeg filters to create video courses so the GUI is aimed towards that use case rather than being flexible: https://blog.modernlearner.org/product-update-split-content-...
The results aren't bad: https://www.youtube.com/watch?v=L-NjLrwTyxs
Great results depend on fine-tuning of the ffmpeg filters and having great quality video to work with.
The ffmpeg filter mini-language is easy to work with when you're targeting a particular use-case.
If you strictly only need to trim/cut, Lossless-Cut (https://github.com/mifi/lossless-cut) may also be an option (and faster).