Video Tools · Browser-based utility
Compress Video Online Free — Reduce Video Size
Reduce video file size using quick presets or custom resolution, CRF, FPS, audio bitrate and x264 encoding-speed controls; output is MP4.
What this tool does
Reduce video file size using quick presets or custom resolution, CRF, FPS, audio bitrate and x264 encoding-speed controls; output is MP4.
People often describe this task with phrases such as compress video online, reduce video size, video size reducer, mp4 compressor, compress mp4 and shrink video. This page uses those terms only where they refer to the same underlying function.
How to use the Video Compressor
- Open the Video Compressor page and select or enter the source data required by the tool.
- Review the available controls instead of accepting defaults blindly when the destination has a size, format, layout or compatibility requirement.
- Run the operation and inspect the preview, status or generated result before treating it as final.
- Download or copy MP4 and verify it in the destination application, browser, viewer or workflow that will actually use it.
Use the interactive tool above for the actual operation. The documentation below explains what the controls mean, what changes in the file/data, and how to troubleshoot common results.
Settings and capabilities explained
| # | Control or capability |
|---|---|
| 1 | Presets: Small, Balanced, High Quality |
| 2 | Resolution: original, 1080p-width, 720p-width or 480p-width |
| 3 | CRF: 0–51 |
| 4 | FPS: original or custom up to 120 |
| 5 | Audio bitrate: 32–320 kbps |
| 6 | Encoding preset: ultrafast, veryfast, medium or slow |
| 7 | MP4 output with H.264 video + AAC audio |
Supported input and output
- Input: browser-selected video
- Output: MP4
How it works technically
Digital video combines time-based video frames and usually audio streams inside a container. Codec, resolution, frame rate, quality controls and audio settings jointly determine compatibility, processing cost and output size.
Video size is driven by duration, codec efficiency, resolution, frame rate, visual complexity, motion, CRF/bitrate behavior and audio bitrate.
CRF is not a fixed-size control. Two videos encoded at the same CRF can have very different sizes because complex motion/noise needs more bits.
Reducing 1920×1080 to 1280×720 lowers pixels per frame from about 2.07 million to 0.92 million—about 56% fewer pixels per frame before considering frame rate.
The x264 preset changes encoder search effort: slower presets can improve compression efficiency but take longer; preset is not itself a quality percentage.
Approximate constant-bitrate size math is size ≈ (video bitrate + audio bitrate) × duration, but CRF output bitrate is content-dependent.
Common use cases
- Reduce a video before upload
- Make a smaller email/message attachment
- Shrink screen recordings
- Downscale 4K/1080p footage for web
- Trade encoding time for file size
Choosing the right settings
- Start with Balanced (720p-style width, CRF 26, 128 kbps audio) for general sharing, then inspect the result.
- Use High Quality when preserving detail matters more than size.
- Use Small for aggressive reduction, especially when mobile viewing is the destination.
- Reduce resolution before pushing CRF extremely high if readability/detail matters.
Common problems and fixes
The output is larger than the input
If the original was already efficiently compressed, re-encoding at a high-quality setting can produce a larger file. Increase CRF, reduce resolution/FPS, or lower audio bitrate.
The browser becomes slow
Video encoding is CPU and memory intensive. Use shorter clips or lower resolution on limited devices.
Compression takes a long time
Try a faster encoder preset or lower output resolution.
Browser processing and privacy notes
The source code for this build performs the documented file transformation or analysis from browser JavaScript/Web APIs, and the video tools load FFmpeg.wasm for media processing. The site also contains third-party analytics, font/CDN and advertising scripts that can make ordinary network requests. Therefore, the precise claim made here is limited to the tool routine: it does not need a separate AutoClip file-upload API in order to perform the documented local operation.
For sensitive files, you should still use your browser’s developer tools or network controls if you need to independently verify the behavior of every third-party request in your environment.
Frequently asked questions
What does the Video Compressor do?
Reduce video file size using quick presets or custom resolution, CRF, FPS, audio bitrate and x264 encoding-speed controls; output is MP4.
What input and output does it use?
Input: browser-selected video Output: MP4 Outputs include MP4.
Do I need to install desktop software?
No desktop installation is required for this page. The interactive workflow runs from the web browser. Some advanced media features load browser-side JavaScript/WebAssembly libraries when needed.
Why can processing take time?
Video decoding and encoding are computationally expensive. The current video tools use FFmpeg.wasm in the browser, so speed depends on source duration, resolution, codec, settings and device CPU/memory.
What CRF should I use?
There is no universal best number. Lower values preserve more quality and usually increase size. The tool’s presets provide practical starting points; compare results on your own content.
Can I compress a video to an exact MB size?
This tool uses CRF rather than a strict two-pass target-size workflow, so exact MB output is not guaranteed.
The output is larger than the input?
If the original was already efficiently compressed, re-encoding at a high-quality setting can produce a larger file. Increase CRF, reduce resolution/FPS, or lower audio bitrate.
The browser becomes slow?
Video encoding is CPU and memory intensive. Use shorter clips or lower resolution on limited devices.