Compress a video (lower bit rate)
Re-encodes a video at a lower bit rate (kbps) to make the file smaller. You can set the maximum height, the audio bit rate and the output format, and the quality becomes lower.
How to use it
- Drag your .mp4 .m4v .webm .mkv .mov files onto the area above, or press "Choose files".
- If options are shown, set them as you like. They appear below the file list.
- Press "Convert". The conversion runs on your device, shows its progress and can be cancelled at any time.
- Press "Download" next to a result. With several results, "Download all as ZIP" gets them in one go.
- The first time, the page downloads the conversion program (about 0.2 MB). It is kept on your device, so later visits do not download it again. Your files are not sent during this step either.
The formats involved
MP4 .mp4 .m4v
MP4 is a container format that holds video, audio and subtitles in one file. The compression used for the video and audio inside can differ from file to file.
WebM .webm
WebM is a video container format made for the web. The compression used for the video and audio inside can differ from file to file.
MKV .mkv
MKV is the Matroska container format that holds video, audio and subtitles in one file. The compression used for the video and audio inside can differ from file to file.
MOV .mov
MOV is the video container format of Apple QuickTime. The compression used for the video and audio inside can differ from file to file.
What changes in this conversion
- The video is re-encoded, so quality can drop. Large files can take a long time and need a lot of memory.
Limits and things to watch for
- On a phone, large files can be slow or fail because of memory limits.
- This is a heavy conversion and can take a while. Progress is shown and you can cancel.
- The file size that can be processed depends on your device. The limit for your device is shown in the drop area, and files above it are refused with a message.
- Writes the Ogg, WebM and MP4 containers around the encoded audio.
- The video and audio codecs that can be used differ from browser to browser. A codec that your browser does not support cannot be converted.
- The resulting video is built in memory, so a very long video can fail by running out of memory.
- Opus encoding needs the browser's AudioEncoder; there is no fallback.
FAQ
Is my file uploaded to a server?
No. Conversion happens only inside this browser, and file names, contents and results are not sent to our servers. Some converters download their conversion program (code) the first time you use them; your files are not sent then either. See the privacy page for details.
Can I convert many files at once?
Yes. Select several files and they are processed one after another; save the results one by one or all at once as a ZIP. How much can be handled at once depends on your device memory and is shown on the page.
Licences and the software used
This converter loads an MPL-2.0-licensed library as unmodified files. The source code is available from the link on the open-source licences page.
Programs this converter downloads and uses: mediabunny 1.62.1 (MPL-2.0) · Open-source licenses
Sources and check date
- Mediabunny 1.62.1: conversion.d.ts (type documentation shipped in the package)
ConversionOptions (video/audio: codec, forceTranscode, rotate, crop, allowRotationMetadata, discard; trim; copy mode/boundaryPolicy), DiscardedTrack reasons · 2026-11-10 - WebCodecs (W3C) - AudioEncoder / AudioDecoder
AudioEncoder and AudioDecoder are [SecureContext] interfaces (Window and DedicatedWorker) · 2026-11-10 - WebCodecs Codec Registry (W3C)
Audio codec strings: mp3, mp4a.*, opus, vorbis (each registration is a separate note) · 2026-11-10
Date we opened the original documents ourselves: 2026-11-10. Specifications can change, so read the original again before anything important.