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 trims the ends and can split a section out of the middle. Where that runs out, why iMovie is overkill for one cut, and what the browser does instead.
Read this before installing iMovie for one cut — QuickTime already does more than most people know, and this is where it stops.
Neither Photos app can speed up an ordinary clip. What the exceptions are, what iMovie and the app stores cost, and how to do it in the phone's browser.
Read this if you went looking for a speed control in Photos or Google Photos and found trim handles instead.
A file that will not open is usually a codec your player cannot decode, not a broken video. How to tell which, and the conversion that fixes most of them.
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 and Samsung Gallery trim the ends of a clip. Why the middle is the case they dodge, and how to remove it in Chrome on the phone itself.
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.
Photos trims the ends, Clipchamp ships with Windows 11, and a browser or FFmpeg does the rest. What each can do, and which to use for a cut in the middle.
Read this to sort out Photos, Clipchamp, a browser tab and FFmpeg on Windows, and pick the one that fits the cut you need.
Dropping the audio stream versus silencing it, the one-line FFmpeg command that does it without touching the video, and what the browser route trades.
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.
A timelapse from an existing recording is an 8× to 16× speed-up with the audio dropped. The frame arithmetic, the FFmpeg command, and the browser route.
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.
Containers are not codecs. What each of the four can carry, where each one plays, and why this editor exports MP4 by default and WebM more slowly.
Read this when an export dropdown asks you to choose a container and you want the honest compatibility picture rather than a guess.
MOV and MP4 share a file structure, so a lossless remux is often possible. Where it breaks — HEVC, ProRes, PCM — and what a browser converter does 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.
Chromebooks have no real video editor. What the Gallery app can and cannot do, why Linux and Android apps are often locked down, and what to use instead.
Read this if the Play Store and Linux are locked down and the Gallery app only trims the ends.
The iPhone Photos app can only trim the start and end of a clip. Here is why, and how to remove a section from the middle without installing anything.
Read this if the Photos app will not remove the bit in the middle — which it will not, by design.
Every browser tool claims to be private. You can verify the claim in about ninety seconds with the tools already in your browser. Here is exactly how.
Read this to check any tool's privacy claim yourself, in about ninety seconds, with the browser you already have.
The exact -ss, -t and -c copy commands for a lossless trim, why the flag order matters, and how to cut a section out of the middle with the concat demuxer.
Read this when you have FFmpeg installed and want the genuinely lossless version, with the exact flag order that makes it work.
Most editors apply one speed to the whole clip. What a per-section speed change actually does to frames and audio, and how to do it in a browser or in FFmpeg.
Read this when you want one stretch of a recording accelerated and the rest left alone — the case most editors handle badly.
Server-based tools cap file size because your upload costs them money. A browser tool's ceiling is the WebAssembly heap; here is how to work within it.
Read this when the file is measured in gigabytes and you want to know what will actually complete.
Trimming only loses quality if the video gets re-encoded. Here is when that happens, when it does not, and the trade you are making either way.
Read this first. Everything else about cutting assumes the stream-copy versus re-encode distinction it explains.
Slowing footage down creates no new frames — it holds the existing ones longer. The frame-rate arithmetic, and why real slow motion has to be shot, not made.
Read this before you slow anything below half speed, so the frame-rate arithmetic is not a surprise.