Video Compressor

What Is Video Compression?

Video compression reduces the amount of data needed to store or transmit a video by removing information that is either redundant or imperceptible to the human eye. Most compressed videos use a codec — a compression algorithm — to encode the raw frames efficiently. H.264 (AVC) is the most widely supported codec and produces small files that play on virtually every device and platform.

Two key settings control how aggressively a video is compressed:

• Bitrate is the amount of data used per second of video. A higher bitrate means more data, better quality, and a larger file. A lower bitrate saves space but may introduce visible artifacts, especially in fast-moving scenes.
• CRF (Constant Rate Factor) is a quality-based encoding mode. Instead of targeting a fixed bitrate, the encoder adjusts the bitrate dynamically to maintain a consistent perceived quality level. Lower CRF values produce higher quality and larger files; higher values produce smaller files with more compression. Values between 18 and 28 cover the practical range from near-lossless to noticeably compressed.

When Should You Compress a Video?

Compression is useful in many everyday situations:

• Email attachments. Most email providers cap attachments at 25 MB. Compressing a recording or clip can bring it well under that limit without requiring a file-sharing service.
• Social media uploads. Platforms like Instagram, Twitter, and WhatsApp re-encode videos on their servers. Starting with a smaller file speeds up the upload and gives you more control over the final quality.
• Web embedding. Videos served directly on websites benefit from smaller file sizes — they load faster and consume less bandwidth for your visitors.
• Device storage. Footage from modern smartphones and cameras can be several gigabytes per minute. Compressing archived clips frees up significant storage space.
• Sharing via messaging apps. Apps like Telegram, Signal, and iMessage have file size limits. Compressed videos send faster and stay within those limits.

Quality vs. File Size Tradeoffs

Compression always involves a tradeoff between visual quality and file size. The right balance depends on how the video will be used:

• For archiving footage you may re-edit later, use a low CRF (18–22) or the High Quality preset to retain as much detail as possible.
• For sharing on messaging apps or via email, the Balanced preset (CRF around 28) typically cuts file size by 50–70% with quality that looks fine on a phone screen.
• When you need to hit a specific file size — for example, a platform upload limit — use Target Size mode, which calculates the bitrate automatically to meet your goal.
• Lowering the resolution is one of the most effective ways to reduce file size. A 1080p video downscaled to 720p can be 60% smaller, and the quality difference is often barely noticeable on small screens.

How This Tool Works

This tool runs FFmpeg compiled to WebAssembly (FFmpeg WASM) entirely inside your browser tab. When you load a video and choose compression settings, FFmpeg re-encodes the file locally on your device using the H.264 codec. No data is sent to any server at any point.

The compression runs in a background worker thread so the browser remains responsive. A progress bar tracks the encoding in real time. Once complete, the compressed file is ready to download immediately.

Your Video Never Leaves Your Device

Because all processing happens in the browser, your video is never uploaded to a server. There is no account required, no storage on third-party infrastructure, and no risk of your footage being accessed by anyone else. This makes the tool safe to use for confidential recordings, sensitive personal videos, or any content you prefer to keep private.

Supported Formats

The tool accepts the most common video formats: MP4, WebM, and MOV. These cover video from smartphones, cameras, screen recorders, and most editing software.

The output is always an MP4 file encoded with H.264. MP4 is supported by every major platform, browser, device, and video editor, so your compressed video is ready to use immediately without any further conversion.

Frequently Asked Questions

Does compression reduce the video quality?

Yes, but the reduction is adjustable. Unlike trimming, compression re-encodes the video, so some quality loss is inherent. At the High Quality preset, the difference from the original is minimal and often imperceptible. At aggressive settings, you may see soft edges or blocking artifacts in fast-motion scenes. Preview the output and increase quality if needed.

Is there a maximum file size?

There is no hard limit enforced by the tool. The video is read directly from disk rather than loaded into memory all at once, so large files can be processed. The main practical constraint is your browser's available memory for holding intermediate encoding data. Most modern devices handle files up to several gigabytes without issues.

Does it work on mobile?

Yes. The tool works in mobile browsers that support WebAssembly, which includes Safari on iOS 15+ and Chrome on Android. Keep in mind that encoding on a phone CPU is slower than on a desktop, so large or high-resolution videos may take a few minutes to process.

What happens to my video after I close the tab?

It is discarded entirely. All video data exists only in your browser's memory for the duration of the session. Nothing is persisted to a server or saved locally after the tab is closed. Make sure to download the compressed file before navigating away.

What does CRF mean and what value should I use?

CRF stands for Constant Rate Factor. It is a quality-based encoding mode where lower numbers mean higher quality and larger files, and higher numbers mean more compression and smaller files. A CRF of 23 is the H.264 default and a good starting point for most uses. Values of 18–22 are considered visually lossless. Values of 28–32 produce noticeably smaller files suitable for messaging apps and web sharing where some quality loss is acceptable.

How does Target Size mode work?

Target Size mode lets you specify the maximum output file size in megabytes. The tool calculates the required average bitrate from the video duration and your target, then encodes at that bitrate. The actual output size will be close to but may not exactly match the target due to how audio and container overhead are accounted for.

Related Tools

You might also find these tools useful:

• Trim Video — Cut a video to a specific segment by dragging start and end handles on a visual timeline, without re-encoding.
• Screen Recorder — Record your screen directly in the browser and save the recording as a video file.