Compress files in your browser

One compressor for photos, videos, music and documents

oCompress makes files smaller so they fit where they need to go: an email attachment, an upload form with a size limit, a messenger, a website, or simply a phone that is running out of storage. Drop a file on the box above and it is routed to the right engine automatically. Images, videos, audio files and office documents can be mixed in one go, and each file gets settings that make sense for its type.

All the work happens inside your browser. The compressors are our own code, built on open-source codecs such as MozJPEG, OxiPNG and SVGO for images and LAME and FLAC for audio, plus the video and audio encoders built into your browser, and they run on your processor. There is no upload, no queue on a server and no copy of your file anywhere but on your own device.

• Images: JPG, PNG, GIF, SVG, TIFF and WebP, with resizing, format conversion and a before/after comparison.
• Video: MP4, MOV, MKV and more, with a target size in megabytes or a quality preset.
• Audio: MP3, WAV, AAC, FLAC, M4A and AIFF, with bitrate, mono and sample-rate controls.
• Documents: PDF, Word, Excel and PowerPoint, with pictures recompressed and the text left untouched.

How much smaller will your file get?

That depends on what is inside it, and no honest tool can promise a fixed percentage. What we can tell you is where the room usually is:

• A lot of room: photos straight from a phone or camera, scanned PDFs, Word and PowerPoint files full of photos, uncompressed WAV and AIFF recordings, and videos recorded on a phone. These are stored generously because the device that made them had to work fast.
• Some room: PNG screenshots, GIF animations, web images saved without optimization, and MP3 or AAC files at high bitrates.
• Little room: files that have already been compressed hard, such as images and videos downloaded from social networks or messengers, text-only PDFs, low-bitrate MP3s and ZIP archives.

The tool shows the size before and after for every file. If the result would not be smaller than what you started with, you keep the original instead of getting a bigger copy.

Which settings to use where

The default preset is a sensible middle ground for every file type. When you have a specific destination, these starting points save you a few rounds of trial and error:

Many email services count the encoded size of attachments, which is about a third larger than the files on your disk, so leave some headroom below the official limit. Our page on file size limits lists the current numbers for Gmail, Outlook, WhatsApp, Telegram, Discord, Slack and others, with links to their help pages.

Lossy and lossless in one minute

Lossless compression stores exactly the same content in fewer bytes; you can always get the original back. PNG in Lossless mode, FLAC audio, ZIP packing and the Light preset for PDF and Office files are lossless. Lossy compression removes detail that people are unlikely to notice: JPEG and WebP photos, PNG in the default Smart mode, MP3 and AAC audio, H.264 video. It achieves much bigger savings, and the settings decide how much detail goes.

Two rules of thumb follow. Compress from the best copy you have, because every lossy step loses a little more. And keep your originals for anything you may want to edit, print or archive later; compressed copies are for sending and publishing. The how it works page explains both kinds of compression in more depth.

Your files stay on your device

Most online compressors upload your file to their server, process it there and let you download the result. That means your contract, your photos or your recording sit on someone else's computer, at least for a while. oCompress works differently: the page loads the compressor code into your browser, and the file is read, compressed and saved locally. You can check this yourself: once the page and the compressor for your file type have loaded, switch off Wi-Fi and compress another file of the same type with the same settings. It still works.

The site is free and financed by advertising, which is shown around the content and never inside the tool. There is no account, no watermark, and no limit on how many files you compress.

What a browser cannot do

Running everything locally has limits, and you should know them before you start a long job:

• Video compression and most audio conversions need WebCodecs, available in current Chrome, Edge and Opera, Firefox 130 or later and Safari 26 or later.
• Very large files, such as long 4K videos or posters scanned at high resolution, can exceed the memory a browser tab may use, especially on phones. On a computer the tool takes video and audio up to 4 GB, PDF and Office files up to 300 MB and images up to 200 MB or 100 megapixels; phones and tablets get lower limits for video, audio and documents (1 GB and 120 MB). A file that is too big gets a clear message.
• Some old formats have no decoder in browsers, notably WMA audio and AVI, WMV, FLV and MPG video, and the binary Office formats DOC, XLS and PPT cannot be rewritten safely. For these, the tool offers what is possible and explains the alternatives.

Common questions

Learn more

Answers to more questions are in the FAQ. If something does not work as expected, or a format you need is missing, tell us.