How to Trim or Cut an MP4 Without Losing Quality

Most clips contain a few seconds you do not want: a fumbled start, a long tail after the action ends. Trimming those off makes the video shorter, smaller and better to watch. How you trim determines whether you keep the original quality, and whether the cut lands exactly where you pointed. This guide covers the built-in tools on common devices, the command-line method for full control, and the one concept (keyframes) that explains almost every surprise.

Understanding keyframes

Video compression does not store every frame as a full picture. It stores a complete frame (a keyframe) every so often, typically every one to five seconds, and in between stores only what has changed. To play from any point, a player has to start at the nearest earlier keyframe.

That has two consequences for trimming:

• Lossless trimming (copying the data without re-encoding) can only begin on a keyframe. If you ask for a start time of 12.0 seconds and the nearest keyframe is at 10.8, the file may start at 10.8, or begin with a short stretch of frozen or black frames.
• Frame-accurate trimming requires re-encoding the first part of the clip so a new keyframe can be placed exactly where you cut. That is slower and recompresses the video a little.

For most casual clips, a lossless cut that is off by a second is fine. For anything where the exact frame matters, re-encode.

On iPhone and iPad

1. Open the video in Photos and tap Edit.
2. Drag the handles at the ends of the timeline strip to choose the start and end.
3. Tap Done, then choose Save Video to replace the original, or Save Video as New Clip to keep both.

Saving as a new clip keeps your original untouched, which is the safer choice.

On Mac

1. Open the file in QuickTime Player.
2. Choose Edit > Trim (or press Cmd+T).
3. Drag the yellow handles to select the part to keep, then click Trim.
4. Choose File > Save or File > Export As to write the result to a new file.

On Windows

Windows 11 includes Clipchamp, a free video editor that can trim by dragging the clip edges on its timeline and exporting to MP4. The built-in Photos app has also offered trimming in some versions. Menus change between Windows updates, so if you do not see these options, use LosslessCut or ffmpeg below.

LosslessCut: a free graphical tool for lossless cuts

LosslessCut is a free, open-source app that cuts video and audio without re-encoding. You open a file, set in and out points on a timeline, and export. It shows you where the keyframes are, which makes the keyframe behaviour above easy to understand in practice. It is a good choice for long recordings, where re-encoding would take a long time.

ffmpeg: full control

Lossless cut (fast, keyframe-limited)

This keeps 13 seconds starting at 12 seconds into the file, with no re-encoding:

ffmpeg -ss 12 -i input.mp4 -t 13 -c copy -avoid_negative_ts make_zero output.mp4

Putting -ss before -i makes ffmpeg jump straight to the point, and -t sets how long to keep. The cut starts at a keyframe near the time you asked for.

Frame-accurate cut (re-encodes)

ffmpeg -ss 12 -i input.mp4 -t 13 -c:v libx264 -crf 18 -preset medium -c:a aac -b:a 160k output.mp4

A -crf of 18 is visually very close to the original. Raise it if you also want a smaller file; see how to compress a video to fit a size limit.

Remove a section from the middle

Cut the file into two parts around the section you want to remove, then join them. Write the parts' file names to a text file, one per line in the form file 'part1.mp4', and run:

ffmpeg -f concat -safe 0 -i list.txt -c copy joined.mp4

Joining with -c copy only works when both parts share the same codec settings, which they will if they came from the same original.

Which method should you choose?

Good habits

• Always keep the original. Trim into a new file. Storage is cheap; the original recording is not replaceable.
• Add a little padding. Start half a second before the action and end half a second after, so the clip does not feel clipped.
• Check the result. Play the trimmed file from start to end, with sound, before deleting anything.
• Name the file clearly. Include the date and what the clip shows, for example 2026-10-19-bug-repro-trimmed.mp4.

Trimming clips you saved from Streamable

If you downloaded your own clip with our Streamable downloader, you have a standard MP4 that any method above can trim. Remember that only videos you own or have permission to use should be edited and re-shared; see copyright and permission basics.

Quick answers