Compress Video

Compressing is the one video operation here that is always a re-encode. Changing containers can copy the existing track untouched; making a file smaller cannot, because the size is a property of how the video was encoded in the first place.

There are no settings to tune: every video is re-encoded as H.264 at a constant-quality level (CRF 28), with AAC audio at 128 kbps, in an MP4. Resolution and frame rate are kept as they are. Because the encoder aims for a level of quality rather than a size, the saving depends on the footage: a talking head or a screen recording shrinks a lot, handheld or fast-moving footage much less, and a phone video already recorded in HEVC may barely shrink at all.

Check the size of the result before you send it, and keep the original if it did not get smaller — compressing the output again costs quality and saves little. Compression runs in your browser through FFmpeg compiled to WebAssembly, so home video — the most personal thing most people convert — is never uploaded.

Best for

• Shrinking a video to fit an email or messaging size limit
• Reducing a clip for a school or work upload portal
• Saving storage or bandwidth on a long recording

What settings the compressor uses

There are no sliders: every video goes through the same recipe. The picture is re-encoded as H.264 with a constant-quality setting (CRF 28) and the "veryfast" encoder preset, the sound is re-encoded as AAC at 128 kbps, and the result is saved as an MP4. The resolution and frame rate are left exactly as they were — a 4K clip comes out 4K, and 60 fps stays 60 fps.

CRF means the encoder aims for a consistent level of visual quality rather than a fixed file size, so how much smaller the file gets depends on the footage. A static talking-head video or a slide recording compresses a great deal. Handheld footage, water, foliage, confetti and fast sport have more changing detail in every frame and come out comparatively larger. That is also why the tool cannot promise a size up front.

When the compressed file isn't smaller

Nothing compares the result with the original before you download it, so look at the size yourself. A video that was already efficiently encoded may barely shrink, or even grow. The usual cases are phone videos recorded in HEVC (H.265), which is a more efficient codec than H.264, clips downloaded from streaming or social platforms that have already been squeezed, and low-bitrate screen recordings.

If that happens, keep the original. Running the compressed MP4 through again applies another lossy encode at the same setting, which costs quality each time while saving little. Shorter is the reliable way to get smaller: send only the part of the recording you actually need.

Why it is slower than a desktop app

The encoder is FFmpeg compiled to WebAssembly, and this site uses its single-threaded build. The multi-threaded build would need special cross-origin isolation headers on every page; the single-threaded one works in every modern browser without them, at the cost of using one processor core. Expect a long video to take a while, and longer on a phone than on a laptop.

The encoding runs in a background worker, so the page stays responsive and shows a percentage as it goes. Keep the tab open and in the foreground — browsers, especially on phones, slow down or suspend tabs you switch away from, and a locked screen can pause the job.

File size limits and device memory

The limit is 500 MB per video, one video at a time. Within that, memory is the real constraint: the whole video is read into the browser's memory, and the compressed copy is built there too before you download it. A long 4K recording near the limit is comfortable on a desktop with plenty of RAM but can exhaust a phone, which typically shows up as the tab reloading itself. For very large files, a desktop browser is the safer place to run it.

Which videos it accepts, and what comes out

The file picker accepts any video type, and FFmpeg reads all the common containers — MP4, MOV, MKV, WebM and AVI among them. The output is always an MP4 with H.264 video and AAC audio, a combination that plays on practically every phone, browser, TV and editor.

The download keeps your file's name with an .mp4 extension. If you started from an MP4, that is the same name as the original, so your browser may add a number to it — check which file you are sending before you delete anything.

The first run, and working offline

The first time you use any video or audio tool here, the FFmpeg engine (about 30 MB) downloads before the conversion starts. The site's offline cache keeps it, so later conversions start quickly and work without a connection. Only the engine is downloaded; your video is never part of that request.

What to do when compression fails

"File too large" means the video is over 500 MB. "FFmpeg produced an empty file — the input may be corrupt or an unsupported variant" means FFmpeg could not make an output from this file: the recording may have been cut off (a phone that ran out of storage mid-recording, an unfinished download), or it uses an unusual codec. Check that it plays from start to finish in a normal player.

If the very first run stops before any progress appears, the engine probably could not download — reconnect and try again; a failed load is retried rather than remembered. Cancel does not interrupt a video that is already encoding, so to stop one, reload the page.

What this tool does

How to convert Video → Compressed Video

Frequently asked questions

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