videocompression Blog

How to Cut Video Without Losing Quality

2026-10-29

How to Cut Video Without Losing Quality

Want to trim the first 30 seconds off a video? The trap most people fall into: they open it in an editor, cut, and export — which re-encodes the entire file and permanently degrades quality. There's a better way: cut *without re-encoding at all*.

The trick: stream copy

Video files are containers holding compressed streams. With ffmpeg you can slice out a section and copy those streams bit-for-bit, no decoding, no re-encoding, zero quality loss — and it's nearly instant:

ffmpeg -ss 00:00:30 -i input.mp4 -t 00:01:00 -c copy output.mp4

This takes 1 minute starting at 0:30. -c copy means "don't touch the codec data." The output is mathematically identical in quality to the source segment.

Cut from a point to the end:

ffmpeg -ss 00:01:15 -i input.mp4 -c copy output.mp4

The keyframe catch (read this)

There's one wrinkle. Video is stored as keyframes (full pictures) plus delta frames (changes). A lossless cut can only *start* cleanly on a keyframe. If your cut point isn't on one, ffmpeg starts at the nearest keyframe before it — so your cut may begin a second or two early, or the first frames may freeze briefly.

Practical fixes:

• Put -ss before -i (as above): fast seeking, snaps to keyframe. Best for rough cuts.
• Put -ss after -i with -c copy: more accurate seeking, but slower and the start may still glitch until the next keyframe.
• Frame-accurate + lossless is impossible in one step — precision requires re-encoding at least a few frames.

When you need frame accuracy

If the cut must land on an exact frame, re-encode — but do it smartly:

ffmpeg -ss 00:00:30.500 -i input.mp4 -t 00:01:00 -c:v libx264 -crf 18 -c:a copy output.mp4

CRF 18 is visually lossless, so the damage is negligible. Or use a smart tool that re-encodes only the few frames around the cut point and copies the rest.

Easiest free tools (no command line)

• LosslessCut (free, open source) — drag, cut, export. Uses ffmpeg under the hood, visual timeline, handles the keyframe logic for you. The best option for most people.
• Avidemux (free, open source) — set markers, choose "Copy" for video and audio, save. Old interface, rock solid.
• Shutter Encoder — also wraps ffmpeg with a friendlier UI.

What NOT to do

Don't "cut" by importing into Premiere/DaVinci/CapCut and exporting with default settings for a simple trim — you'll wait through a full re-encode and lose a generation of quality for nothing. Save the editor for actual editing.

Bottom line

For simple trims, never re-encode: ffmpeg -c copy or LosslessCut gives you a perfect, instant, zero-loss cut. Reserve re-encoding for when you also want to *compress* — and for that, our free online video compressor handles MP4 and WebM right in your browser.