How to trim a video without losing quality on Mac

Why re-encoding hurts quality

Modern video codecs like H.264 and HEVC are lossy by design - they throw away information that the human eye is unlikely to notice in order to store video at manageable file sizes. Every time you decode and re-encode, that lossy process runs again on data that was already compressed. Artefacts compound: blocking, ringing, colour banding, and detail smearing that weren't visible in the original creep into the picture.

Even encoding at a very high bitrate doesn't fully recover what was lost in a previous compression pass - you're working from degraded data. The only way to avoid this cycle entirely is to never decode in the first place.

How lossless trimming works

When you set an in point and an out point, Lossless Video Cutter identifies the keyframes nearest to your cut positions. Keyframes are the self-contained reference frames that the codec uses as anchors - every other frame in between is stored as a delta relative to the nearest keyframe. Because the delta frames can't stand alone, cuts must align to keyframe boundaries.

Once the keyframe boundaries are determined, the app uses AVFoundation to read the compressed sample buffers - the raw packets - and writes them directly into the output container. No pixel decoding, no colour conversion, no encoder pipeline. The video data in the output file is bit-for-bit identical to the corresponding data in the source.

Supported formats

Lossless Video Cutter works with all the formats you're likely to encounter on a Mac:

Step-by-step

1. Open your video with ⌘O or drag it onto the app window.
2. Set the in point by scrubbing to the start of the section you want to keep, then pressing I.
3. Set the out point by scrubbing to the end of the section and pressing O.
4. Preview the selection using the play button or spacebar to confirm the cut feels right.
5. Export with ⌘E. The output file is ready in seconds - no re-encode wait.

The keyframe caveat

Because lossless trimming requires cuts at keyframe boundaries, the actual cut position may shift slightly from where you placed your in or out point - typically by a fraction of a second. The app snaps to the nearest keyframe automatically and shows you the precise cut frame in the preview so there are no surprises.

For most content this is imperceptible. Camera footage typically has keyframes every half second or so; screencasts and static content can have them even more frequently. If you're working with highly compressed material that has keyframes only every few seconds, you can set a slightly earlier in point to give the snap more room. The preview always reflects the actual cut, not your raw cursor position.