Does my video file get uploaded anywhere?

No. All analysis happens entirely in your browser using the HTML5 video element and File API. Your file never leaves your device and no data is sent to any server.

Why can't the tool compress the video directly in the browser?

True video re-encoding (changing codec, bitrate, and resolution) requires substantial CPU processing that browsers cannot do efficiently or universally. FFmpeg is the standard tool for this and produces far better results. The tool gives you the exact FFmpeg command so compression is one paste away.

What does CRF mean in the FFmpeg command?

CRF (Constant Rate Factor) controls quality vs. file size in H.264 and H.265. Lower values mean higher quality and larger files. For H.264: 18 is near-lossless, 23 is default (good quality), 28 is visibly compressed. For H.265: equivalent quality is achieved at 4–6 CRF points lower than H.264.

Why does the estimated output size differ from the actual compressed file?

The estimate is based on average bitrate * duration. Real encoders vary bitrate per scene (CBR vs. VBR), so complex scenes use more bits and simple scenes fewer. Actual results typically fall within 10–20% of the estimate for VBR encodes.

How do I install FFmpeg?

On macOS: brew install ffmpeg. On Ubuntu/Debian: sudo apt install ffmpeg. On Windows: download a build from ffmpeg.org/download.html or install via winget (winget install ffmpeg). After install, the command shown in this tool runs directly in your terminal.

What does -movflags +faststart do in the FFmpeg command?

It moves the MP4 metadata (moov atom) to the beginning of the file so browsers can start playing the video before it fully downloads. Recommended for any video served over HTTP.

Video Compressor

Name: Video Compressor
Availability: InStock
Author: Nham Vu

Analyze your video file in the browser — see size, duration, and resolution — then get estimated output sizes at different bitrates and a ready-to-run FFmpeg command.

Drop a video file here

or click to browse — MP4, MOV, MKV, AVI, WebM, FLV & more

Load a video file to see compression estimates and FFmpeg commands.

Copied!

Summary

Analyze your video file in the browser — see size, duration, and resolution — then get estimated output sizes at different bitrates and a ready-to-run FFmpeg command.

How it works

Drop or select any video file (MP4, MOV, MKV, AVI, WebM, etc.).
The browser reads the file metadata: size, duration, resolution, and calculated bitrate.
Choose a target bitrate from the presets or enter a custom value.
The tool estimates the output file size based on the target bitrate and duration.
Copy the generated FFmpeg command and run it in your terminal to compress the file.
Adjust the quality preset in the FFmpeg command (CRF value) to fine-tune results.

Use cases

Quickly estimate how small a video will be before committing to a long encode.
Get a correct FFmpeg command without memorizing codec flags.
Check if a recorded video is already within a size limit before uploading.
Compare estimated sizes at different bitrates to find the best quality/size trade-off.
Prepare videos for email attachments, web upload, or storage limits.
Learn what bitrate your source video uses to decide if compression is even needed.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu