Trimming a long video in seconds with a lossless cut

Most of the time, when you want to cut a video, you aren't making a film. You've recorded a long stretch and you only want part of it. The first ten minutes of a school concert before anyone came on stage. A phone video that starts with your thumb over the lens. A recording of a TV programme with half an hour of something else on either side. For jobs like these, a full editor is overkill, and Cut by Zaweba is built for exactly this sort of thing.

The quickest way to save a cut in Cut by Zaweba is a lossless cut. It's fast, it doesn't touch the quality, and on most videos it's all you need.

What lossless actually means

A video file is made of packets of compressed picture and sound. Normally, when you trim a video in an editor, the editor decodes all of that, cuts it, and compresses it all over again on the way out. That takes time, often as long as the video itself or more, and each round of compression loses a little quality.

A lossless cut skips all of that. Cut copies the original packets you want to keep straight into the new file, without re-encoding anything. The picture and sound in the result are exactly what was in the original, bit for bit. And because there's no compression to do, it's quick: an hour-long file is done in seconds.

How to make one

Open your video and find the part you want. You can step through frame by frame, jump between keyframes, or type in a time. Mark the start with I and the end with O. The scrub bar shows what you're keeping and what you're cutting, so you can see at a glance whether you've got it right. Then save.

If you want to remove several bits, such as adverts from a long recording, you can mark more than one part to keep. Only the kept parts end up in the saved file.

The one catch

Lossless cuts have one limit, and it's worth understanding. Video is compressed using keyframes, which are complete pictures, with the frames in between stored as changes from them. A lossless cut can only start at a keyframe, because a frame between keyframes doesn't make sense on its own.

So when you mark a start point, a lossless cut may snap back to the nearest keyframe and keep a little extra at the beginning. Cut is upfront about this. The Cut tab explains in plain words how far a lossless cut will snap and how much extra it keeps. For most jobs, a second or so of extra footage at the start is nothing to worry about.

When to use it

Lossless cuts are ideal whenever speed and quality matter more than landing on the exact frame. Trimming a phone video before sending it. Cutting dead air out of a recording. Splitting a long file into chunks. Pulling one song out of a concert recording. In all of these, a second of extra footage either side is fine, and keeping the original quality is a bonus.

If you do need the exact frame, perhaps because you're cutting right on a word or on a scene change, Cut has a smart cut for that. It re-encodes only the few frames around each cut and copies the rest, so it's still quick. The Cut tab's explanation is what helps you choose: if the lossless snap is tiny, stick with lossless; if it's keeping something you don't want, switch to smart.

Gentle on any PC

Because a lossless cut does so little work, it runs well even on old or modest PCs. Cut by Zaweba was made with those machines in mind, and it switches on a lighter low-spec mode by itself when it notices one. But a lossless cut barely needs it. There's no encoding, so there's nothing for a slow processor to struggle with.

It opens most video you're likely to have, including MP4, MKV, MOV, AVI, WebM, WMV, MTS, M2TS, TS, FLV and more. If you've got a video that's too long and you just want the good bit, a lossless cut is almost always the place to start.