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Crop Video

Drag a rectangle over the frame and keep only what is inside it. Runs entirely in your browser.

Why crops have to land on even pixels

H.264 does not store a colour value for every pixel. Human vision is far more sensitive to brightness than to colour, so the format keeps full-resolution brightness and one colour sample per 2×2 block — a trick called chroma subsampling that saves a great deal of space for no visible cost.

It does mean a frame has to divide evenly into those blocks. A crop 401 pixels wide, or one starting at x=17, cuts a colour block in half, and the encoder refuses the job rather than guessing. Tools that pass the selection straight through produce a failure that talks about pixel formats and says nothing about the rectangle you drew.

So the rectangle is rounded down to even numbers on every side before it reaches the encoder, silently. At most one row and one column go missing, which nobody can see, and the alternative is an error nobody can act on.

Aspect presets and the fraction trap

Your selection is held as fractions of the frame rather than pixels, so that it survives the video being displayed at whatever size fits your screen. That is the right way to store it and the wrong way to apply a ratio: a selection half as wide and half as tall as a 16:9 frame is not square, it is 16:9.

The presets convert into real pixels, apply the ratio there, and convert back. A 1:1 selection is a genuine square in the output file, which is what a social platform will measure it as.

Cropping never scales up

You get exactly the pixels inside your rectangle, at the resolution they already had. A tight crop of a 4K clip is still sharp; the same crop of a 480p one is not, because there was never any more detail there. No amount of processing invents it, and anything claiming otherwise is guessing at pixels.

Crop Video FAQ

Is my video uploaded?

No. The frame you drag over is played locally by your browser, and the crop itself runs through WebAssembly on your own machine. Nothing is sent anywhere.

Does cropping reduce quality?

The pixels you keep are re-encoded once, because removing part of the frame changes its dimensions and a video's frames are compressed relative to one another. At the default quality that single generation is not visible. What cropping does not do is scale anything up: you get exactly the pixels that were inside your rectangle, at their original resolution, which is why a small crop of a large video is sharper than the same crop of a small one.

Why did my crop come out a pixel or two smaller than I drew?

Because H.264 stores colour at half resolution — one colour sample for every 2×2 block of brightness — so a crop with an odd width, height or offset has no clean boundary to cut on. Encoders refuse it outright. Rather than showing you a codec error about your selection, the rectangle is quietly rounded down to even numbers. At most one row and one column of pixels are lost, which is invisible.

Do the aspect presets give exact ratios?

Yes, and it is less obvious than it sounds. Your selection is stored as a fraction of the frame, so a selection that is 'square' in those terms is only actually square on a square video — on a 16:9 clip it would come out as a wide rectangle. The presets convert into real pixels before applying the ratio, so 1:1 is a genuine square and 9:16 is a genuine vertical.

Can I crop and keep the audio?

Yes. Cropping only changes the picture; the sound is carried through. It is re-encoded to AAC because the output is an MP4, which cannot hold every audio format a source file might use.