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.