ZeroUtil

Video Compressor

Compress MP4, WebM and MOV videos with H.264 to make them smaller for sharing. Files auto-deleted after 15 minutes.

Maintained by

How to Compress a Video Online

  1. Drop your video file onto the upload area. MP4, WebM, MOV and MKV up to 500 MB are accepted.
  2. Pick a compression preset: higher quality (CRF 23, larger file), balanced (CRF 28, default), or smallest size (CRF 32, more visible artifacts).
  3. Press Compress. The file uploads to our EU servers, FFmpeg re-encodes it with H.264 + AAC, and you download the smaller MP4.
  4. Both the original and the result are auto-deleted within 15 minutes. We do not log, store or analyse the content.

How CRF affects file size

CRF (Constant Rate Factor) is the H.264 quality knob. Lower CRF means more bits per pixel, which means a larger file at higher visual quality. CRF 18 is "visually lossless", CRF 23 is the libx264 default for archival quality, CRF 28 cuts file size by roughly half compared to 23 with quality drop visible only on careful comparison, and CRF 32 is suitable for thumbnails or chat attachments where size matters more than detail.

The compressor uses the fast encoder preset, which is the sweet spot of speed vs efficiency. medium would be ~10 percent smaller for the same CRF but takes 2x longer; veryfast is faster but ~10 percent larger. Most users do not notice the difference for short clips, so we lock fast as the default.

When to compress before sharing

  • WhatsApp, Telegram, Discord and email attachments cap files between 25 and 200 MB depending on the channel - compressing a 4K phone clip down to ~30 MB is usually enough.
  • Embedding a demo into a Notion page, Slack thread or GitHub issue: smaller files load faster on mobile.
  • Saving disk space on a phone or laptop: a 30-second screen recording can drop from 80 MB to 10 MB with no visible change for most viewers.

Frequently Asked Questions

Does compression reduce video quality?

Yes - H.264 with CRF 28 is a lossy codec, meaning some detail is discarded. Most viewers do not notice the loss at typical playback sizes (phone, laptop) because the encoder is tuned to drop information humans are bad at perceiving (high-frequency detail in busy regions). For archival originals keep the source file; use the compressed version only for sharing or web embedding.

Why does the output use MP4 even if I uploaded WebM?

MP4 with H.264 + AAC has the broadest playback support across iOS, Android, browsers, social platforms, messaging apps and old hardware. WebM with VP9 is more efficient at the same quality but Safari iOS only added partial support recently and many editing apps still cannot import it. We pick MP4 to maximize "open and play" success.

How small will my video become?

It depends on the source. A high-bitrate phone clip (50-80 Mbps) typically shrinks 5-10x at CRF 28. An already-compressed YouTube download (1-3 Mbps) might shrink only 30-50 percent because most of the redundancy is already gone. Screen recordings with large flat regions compress dramatically.

Does this re-encode hurt video that has been compressed before?

Yes, slightly. Each lossy re-encode discards some detail. For best quality always start from the original capture. If you are compressing a YouTube download or a clip a friend re-uploaded, the result is a compression of an already-compressed source - the artifacts compound.

How long does compression take?

Roughly real-time on modern hardware: a 60-second clip takes around 60 seconds plus upload time. 4K and high-FPS clips take 2-3x longer. If the job exceeds 10 minutes the server kills it and returns an error.

What is the file size limit?

500 MB per upload in this browser tool. For larger files (2 hour movies, raw camera footage) use FFmpeg locally on your machine - the same command we run is `ffmpeg -i input -c:v libx264 -preset fast -crf 28 -c:a aac -b:a 128k output.mp4`.

Are my files private?

Files travel over HTTPS to api.zeroutil.com (EU server). FFmpeg processes them locally on the server, returns a signed download URL, and both input and output are auto-deleted after 15 minutes. We do not log file content, do not feed it to any model, and do not retain it beyond the deletion window.

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