Large videos can exceed email and messaging limits or take a long time to transfer. The video compressor runs FFmpeg through WebAssembly, so your video is processed locally in your browser without being uploaded to a server.
How to compress a video
- Open Video Compression and click Select File.
- Choose an Output Format; the default is mp4.
- Adjust Quality; the default is 75.
- Check Forecast, the estimated output size, then click Start.
5. When processing finishes, click Download. Use Stop to cancel during conversion.
The first conversion requires the FFmpeg core to load. Further conversions on the same page reuse the loaded engine.
How the quality setting works
File size is approximately bitrate × duration. The tool:
- Reads the duration and estimates the original average bitrate from file size and duration.
- Multiplies that estimate by the selected quality percentage to obtain a target video bitrate.
- Re-encodes the video with FFmpeg.
For example, a 100 MB video lasting 100 seconds has an average bitrate of roughly 8,000 kbps. At quality 50, the target video bitrate is about 4,000 kbps, so the result may be around half the original size.
Forecast uses original file size × quality percentage. Audio tracks, encoder behavior, and scene complexity affect the actual result, so this is an estimate rather than an exact size limit.
Suggested quality settings
- Keeping a result close to the source: start around 70–85 and inspect the output.
- Sharing through messaging or email: try 40–60 for a smaller file.
Meetings and tutorials where readability matters most: try 20–40, especially for mostly static scenes, and check that text remains readable.
Low bitrates can cause blocking and lost detail, particularly in fast-moving scenes. A setting of 50 is a useful starting point, but the right value depends on the source.
Supported formats
- Input: formats such as MP4, MKV, AVI, and MOV, subject to browser metadata support and the available codecs.
- Output: mp4, mkv, avi, flv, mov, webm, and m4v.
MP4 is a practical default for sharing. WebM can be useful for web playback.
Ways to make the result smaller
- Shorten the video with Video Clip. Keeping only the useful portion reduces the amount of footage to encode.
- Crop unnecessary areas using the same tool to remove borders or unrelated content.
- Keep only the sound with Extract Audio from Video.
Frequently asked questions
Why is compression slow?
This browser-based FFmpeg workflow does not use desktop-style GPU encoding. Processing time depends on your CPU, resolution, and video duration. Trimming long footage first can help.
How large can a video be?
Available browser memory limits the practical size. Start with files of a few hundred megabytes or less on a desktop browser; this is a guideline, not a guaranteed limit.
What if conversion fails?
The codec may be unsupported, or the file may exceed available memory. Try another output format or a shorter video.
