Filewhisk

Trim a video, and know what is still in the file

Drop a video here

or click to choose — MP4, MOV, M4V, WebM, MKV

Set a start and an end, then choose how to cut. Keep quality copies the video without re-encoding it, which is fast and loses nothing — but a video can only be cut that way at a keyframe, so the file quietly keeps a second or two before your start and tells players to skip it. This one tells you exactly how many seconds are hidden in the file and lets you start on the keyframe instead, or cut exactly by re-encoding the part you keep. Nothing is uploaded.

How to trim a video

  1. Drop an MP4, MOV, M4V, WebM or MKV into the box above. The line under it shows the length, picture size and how often the file has keyframes.
  2. Set Start and End. Type seconds (65.5) or minutes and seconds (1:05.5), or pause the preview where you want and press Use current time.
  3. Choose Keep quality or Cut exactly, and read the plan line under the choice. It says where the file will really begin.
  4. Press Trim video, play the result on the page, and download it.

Why a lossless cut cannot start just anywhere

Compressed video does not store every frame as a picture. Every so often there is a keyframe, a complete image; the frames after it only record what changed. That is why video files are small, and it is also why you cannot cut the stream at an arbitrary frame without re-encoding: a frame that says “move this bit slightly left” is meaningless once the picture it refers to has been cut away.

So a trimmer that does not re-encode has two choices when your start falls between keyframes. It can move your start to a keyframe, or it can copy from the keyframe before your start and write a small instruction into the file (an edit list) telling players to begin at the time you asked for. The second is the usual approach, and browsers and most players follow the instruction. What it does not do is remove the footage in between.

What we measured

Our test clip is 12 seconds of 1080p video at 30 fps with a keyframe every 2 seconds (at 0, 2, 4, 6, 8 and 10 s) and AAC sound. We asked for 5.30 s to 9.00 s and read the output with an MP4 parser written separately from this page:

Keep qualityKeep quality, start on keyframeCut exactly
Video data in the file starts at4.00 s4.00 s5.30 s
Players open it at5.30 s4.00 s5.30 s
Footage before your start still in the file1.30 s (39 frames)nonenone
Frames re-encoded00all

The 1.30 seconds are skipped by browsers and most players (we checked Chrome), which is why this kind of trim looks perfect. But a video editor, a frame-extraction tool or anyone reading the file directly can see them. For a clip where the cut-away part is simply boring, that does not matter. For a clip where it must not be seen — a face, a name, a screen — it matters a great deal, and a trimmer should say so. This page names the exact number of hidden seconds before you cut, offers to start on the keyframe so nothing is hidden, and offers the frame-exact route when the start has to stay where it is.

Which one to choose

  • Keep quality when you are only tidying a clip: it is instant and nothing is lost.
  • Start on the keyframe when a slightly earlier start is fine and you want nothing hidden: still instant, still lossless.
  • Cut exactly when the first frame has to be precisely right, or the part you are removing must really be gone. It re-encodes the part you keep at about the original bitrate, which takes longer and softens detail a little.

The end of the clip works the same way in all three: the file stops at the end you set. After each trim the page lists what came out — the kept range, the new length and size, how many frames were copied unchanged, and how much is hidden before the start — so you can check before you download.

Everything runs in your browser. The video is not uploaded, there is no size limit, and there is no account.

Frequently asked questions

How do I trim a video?

Drop the video in, then set the start and end - type the times, or pause the video where you want and press Use current time. Choose Keep quality or Cut exactly, read the one-line plan under it, and press Trim video. You can play the result on the page before downloading it.

Can I trim a video without losing quality?

Yes: Keep quality copies the compressed frames into the new file without re-encoding them, and the page compares them with the original byte for byte to show that none changed. The catch is where the cut can start. Compressed video is made of keyframes, which are complete pictures, and frames in between that only describe changes. A copy has to begin on a keyframe, because the frames after it make no sense without it.

What is hidden in the file after a lossless trim?

If your start is not on a keyframe, the video data starts at the keyframe before it, and a note in the file tells players to begin at your start time; browsers and most players follow it. In our test clip, with a keyframe every 2 seconds, a trim from 5.30 s kept video from 4.00 s: 1.30 s that normal playback skips but that is still in the file. Video editors and frame extractors can show it. If that part must not be seen, use Start on the keyframe, which makes the cut clean, or Cut exactly.

What does Cut exactly do differently?

It decodes the part you keep and encodes it again as H.264 at about the original bitrate. The new file starts and ends on the exact frames you chose and contains nothing else. It takes longer and, like any re-encode, loses a little detail.

How far apart are keyframes?

It depends on what made the video. Phones and cameras commonly put one every one or two seconds; screen recordings and some exported files can go much longer. The page shows the average gap for your file as soon as it is read, and the plan line names the keyframe your cut will start from.

Which formats work?

MP4, MOV and M4V; WebM and MKV where your browser can read them. A lossless trim keeps the original format family: MP4-family files come out as MP4 and WebM stays WebM. Cut exactly always produces an H.264 MP4.

Is my video uploaded?

No. The file is read and cut by your browser. Nothing is sent anywhere, there is no file size limit, and no account. A lossless trim takes well under a second for a short clip because nothing is decoded.

Can I also make the result smaller?

Trimming removes length, which is often the best way to get under a size limit. If it is still too big, take the trimmed file to Compress video, and use Mute video if you also want the sound gone.

Video to Frames Decoded frame by frame, so the count is exact. Mute Video Every frame checked against the original. Video to GIF Set the size limit and let the tool find the settings. Compress Video Measured after encoding, not estimated before. Extract Audio from Video Copied out of the file, not converted.