Everything is extremely fast because it does an almost direct data copy, fueled by the awesome FFmpeg which does all the grunt work.

Or you can add a music or subtitle track to your video without needing to encode. It lets you quickly extract the good parts from your videos and discard many gigabytes of data without doing a slow re-encode and thereby losing quality. The main feature is lossless trimming and cutting of video and audio files, which is great for saving space by rough-cutting your large video files taken from a video camera, GoPro, drone, etc. LosslessCut aims to be the ultimate cross platform FFmpeg GUI for extremely fast and lossless operations on video, audio, subtitle and other related media files. Update automatically or install from the portable app store in the Platform. And it's open source and completely free. It's packaged in Format for easy use from any portable device and integration with the Platform. Lossless Cut is a lossless video and audio cutter to trim media files without re-encoding. A new version of Lossless Cut Portable has been released.

Lossless cut github