Cutting and retiming video looks like it should be simple, and the reason it is not comes down to a handful of facts about how codecs store frames. These guides explain those facts well enough that you can predict what a tool will do to your file before you press the button.
A video file is not a sequence of pictures. It is a container wrapping a compressed stream in which most frames are not whole images at all — they are descriptions of how the picture changed since the frame before. Only occasional keyframes stand on their own.
Almost everything that feels arbitrary about video editing follows from that. It is why a "lossless" cut lands somewhere near, rather than exactly on, the second you asked for. It is why changing speed can never be lossless, because the timing lives inside the compressed stream. It is why removing a section from the middle is a fundamentally harder operation than shortening the ends, and why so many tools only offer the easy one.
The recurring trade is between exactness and generation loss: you can have the cut exactly where you want it, or you can have the original bytes untouched, and no tool can give you both at once. Every guide below is an application of that.
Want to apply it now? Cut a section out of a video, speed part of one up or slow part of one down — nothing is uploaded.
QuickTime Player trims a video on a Mac and can split out a middle section. Plus a free browser editor and FFmpeg for the cuts QuickTime cannot make.
Read this before installing iMovie for one cut — QuickTime already does more than most people know, and this is where it stops.
iPhone Photos and Google Photos can't speed up an ordinary clip. Speed up a video on your phone in Safari or Chrome: free, no app, no watermark, pitch-correct audio.
Read this if you went looking for a speed control in Photos or Google Photos and found trim handles instead.
A video that won't play is usually a codec your player can't decode, like HEVC — not a broken file. Find the codec, then convert to H.264 MP4 to fix it.
Read this when a file refuses to open, to work out whether it is the codec, the container, the audio track or a genuinely broken download.
Google Photos only trims the ends and Samsung Gallery's split depends on your One UI. To cut the middle out of a video on Android, use Chrome: no app, no upload.
Read this if Google Photos or Samsung Gallery will only move the ends in, and you want the middle gone without a Play Store subscription.
Cut a video on Windows 10 or 11: Photos trims the ends, a free browser editor cuts the middle with no install, and FFmpeg (one winget command) does it losslessly.
Read this to sort out Photos, Clipchamp, a browser tab and FFmpeg on Windows, and pick the one that fits the cut you need.
Remove audio from a video losslessly with ffmpeg -i in.mp4 -c:v copy -an out.mp4, or mute it free in the browser. Dropping vs silencing the audio track.
Read this for the one-line lossless command, and to know exactly when the browser route copies the video and when it re-encodes it.
To make a timelapse from a video, speed it up 8× to 16× and drop the audio. Steps for a free browser tool, the FFmpeg command, and which speed to pick.
Read this before speeding a recording past 8×, so you pick the factor by how fast the subject moves rather than by the runtime you want.
Use MP4 (H.264 + AAC) when a video has to play everywhere. How MP4, MOV, MKV and WebM differ, what codecs each holds, and where each one plays.
Read this when an export dropdown asks you to choose a container and you want the honest compatibility picture rather than a guess.
A MOV often becomes an MP4 losslessly with ffmpeg -i in.mov -c copy out.mp4, a remux, not a re-encode. When it fails (HEVC, ProRes, PCM) and what to do instead.
Read this before converting a MOV, to find out whether a two-second lossless remux will do or the codecs inside force a re-encode.
Trim the ends in the Gallery app; to cut the middle, use a free editor that runs in Chrome. No Play Store, no Linux, no upload — fine on school devices.
Read this if the Play Store and Linux are locked down and the Gallery app only trims the ends.
Photos only trims the ends. To cut a section out of the middle of an iPhone video, open a free browser editor in Safari and mark it — no app, no upload.
Read this if the Photos app will not remove the bit in the middle — which it will not, by design.
Check whether an online video editor uploads your file in 90 seconds: watch the Network tab in DevTools while it works, then repeat the edit offline.
Read this to check any tool's privacy claim yourself, in about ninety seconds, with the browser you already have.
ffmpeg -ss 1:30 -i in.mp4 -t 45 -c copy out.mp4 trims losslessly. Why -ss goes before -i, -t vs -to, keyframe snapping, and cutting the middle of a video.
Read this when you have FFmpeg installed and want the genuinely lossless version, with the exact flag order that makes it work.
To speed up part of a video, mark that section and set a speed; the rest plays normally. Do it free in a browser or in FFmpeg, with pitch-correct audio.
Read this when you want one stretch of a recording accelerated and the rest left alone — the case most editors handle badly.
Upload tools cap file size to save bandwidth. A browser editor has no cap, only a memory limit: ~1–2 GB on a desktop. How to trim large videos within it.
Read this when the file is measured in gigabytes and you want to know what will actually complete.
A trim is lossless if the video is stream-copied, not re-encoded — but then it can only cut at keyframes. How to trim losslessly, and the trade-off.
Read this first. Everything else about cutting assumes the stream-copy versus re-encode distinction it explains.
Slowed-down video looks choppy because no new frames are made: 30 fps at 0.25× is 7.5 frames a second. How slow you can go, and how to shoot it smooth.
Read this before you slow anything below half speed, so the frame-rate arithmetic is not a surprise.