My video camera records into .MTS files and splits them into 1GB bits.

I mostly use the camera to tape shows of my band.

I need a tool that will let me mark an area (i.e. the duration of a song) and export it into another file format so I can put it on Youtube. But it'll have to work well across split files since the camera might split in the middle of a tune. Ideally, I'd like to mark all the ranges that contain tunes and then either export them in a queue or similar.

It might also help to have a bit of other features, e.g. brightness/contrast or a bit of cropping, and it would be a bonus to be able to sync an external audio file (from a better audio recorder) into it all and edit it along with the video material (I've given up on this for the time being but might want to do it again some day).

I currently use LightWorks, but it is really cumbersome for what I need.

Ideally, I'd love a free tool, but if it's good for what I do I'll buy it.

I tried Openshot, but that only exports one video you compose out of multiple materials.
I tried VSDC, but it also was too cumbersome for what I need.

Hopefully, there's something out there for this.