How to trim MKV video files on Mac without converting them

The MKV compatibility problem on Mac

AVFoundation - Apple's native media framework - does not support MKV as a container. This means most Mac apps built on AVFoundation will either refuse to open an MKV file, show an error, or silently transcode it in the background before displaying the timeline. The transcoding adds time, uses CPU, and introduces a quality loss before you've even made your first cut.

Lossless Video Cutter solves this by bundling its own MKV muxer/demuxer. The app reads compressed packets directly from the MKV container and writes them to the output - no conversion step, no intermediate file.

Supported MKV codecs

Compressed packets are read from the MKV container and written to the output without re-encoding. The video and audio data in the output file are bit-for-bit identical to the source.

Step-by-step: trim an MKV file

1. Open your MKV file with ⌘O or drag it directly onto the app window.
2. Navigate to your in-point. Use the timeline scrubber or arrow keys for frame-by-frame navigation.
3. Set the in-point with I. The app snaps to the nearest keyframe and shows the actual cut boundary.
4. Set the out-point with O.
5. Export with ⌘E. Choose MKV as the output format to keep the original container.

Exporting MKV back to MKV vs MP4

If your source is MKV and your output is also MKV, the video track is copied losslessly - the container changes only in that it contains fewer packets (the trimmed segment). If you export to MP4 and your source codec is H.264 or HEVC, the export is still lossless.

One case where you should keep MKV as the output: if your source has DTS audio. DTS is not supported in MP4, so exporting to MP4 with a DTS audio track will either fail or require the audio track to be re-encoded. Keep the MKV container to preserve DTS pass-through.

Common MKV use cases