Video Optimizer

Reduce video file size while maintaining good quality, processed in your browser with ffmpeg

Drop a video file (MP4, WebM, MOV, AVI...)

Shrink a Video by Tuning CRF, Resolution, and Audio Bitrate Together

This tool re-encodes a video using either libx264 (MP4) or libvpx-vp9 (WebM), with quality controlled by CRF, a constant rate factor that tells the encoder how much detail to preserve rather than targeting a fixed bitrate directly. Every scale operation runs through a Lanczos-filtered scale, which resamples pixels using a sharper, higher-quality kernel than the bilinear scaling many quick tools default to, so downscaled footage keeps more perceived sharpness. The four presets (Social media, Web balanced, High quality, Maximum compression) are really just shortcuts that set a CRF value, a target width, and an audio bitrate together, but every one of those three values is also exposed as its own slider for manual tuning.

Audio is handled separately from video: you can pick a bitrate from 64kbps up to 256kbps, or strip the audio track entirely with the Remove Audio checkbox to shave off extra size when the clip doesn't need sound. Because CRF and resolution both affect file size independently, and often multiplicatively, cutting a 1080p source to 720p and simultaneously raising CRF a few points tends to produce a much bigger size reduction than adjusting either one alone. All of this runs through ffmpeg.wasm inside the browser tab, so nothing about the source video is transmitted anywhere during the process.

How to Use

1
Upload the video to shrink
MP4, WebM, MOV, MKV, and AVI files are all accepted as input.
2
Start from a preset, or skip to manual controls
Social media, Web (balanced), High quality, and Maximum compression each set a CRF, a width, and an audio bitrate in one click.
3
Fine-tune CRF and resolution
Drag the CRF slider between 10 (near-lossless) and 40 (heavy compression), and optionally uncheck 'Keep original' to cap the output width with Lanczos scaling.
4
Set the audio bitrate or drop audio entirely
Pick a bitrate from 64 to 256 kbps, or check 'Remove audio' for a video-only file, useful for silent background loops or muted clips.
5
Optimize and compare sizes
The result screen shows the original size next to the new one, so you can judge whether to compress further before downloading.

Key Features

→CRF and resolution both shrink file size independently, combining a lower resolution with a slightly higher CRF usually beats pushing either one to an extreme by itself.
→The scale filter here uses Lanczos resampling, which holds onto more detail when downscaling than a plain bilinear resize would.
→WebM (VP9) output generally lands smaller than MP4(H.264) at a comparable CRF, but MP4 has broader compatibility with older players and editors.
→If the clip doesn't need sound, checking 'Remove audio' cuts out an easy chunk of size, especially at higher audio bitrate settings.
→CRF around 23 is libx264's own default and a reasonable starting point; treat the four presets as starting points to tweak rather than fixed answers.
→Going from 1080p to 720p width typically halves pixel count per frame, which is why resolution changes tend to move file size more than CRF tweaks alone.

Frequently Asked Questions

What does the CRF slider actually control?

CRF (Constant Rate Factor) tells the video encoder how aggressively to compress, on a scale where lower numbers preserve more detail and produce larger files, and higher numbers compress harder. It's a quality target rather than a fixed bitrate, so the actual output size still depends on how complex the footage is.

Why does the tool scale with a 'Lanczos' filter specifically?

Lanczos scaling uses a sharper resampling kernel than simple bilinear or nearest-neighbor resizing, so it tends to preserve more perceived detail when shrinking a frame down, at the cost of slightly more processing time.

Does lowering resolution or raising CRF save more space?

Both reduce size, but they compound: halving the width roughly quarters the pixel count per frame, while a higher CRF reduces the bits spent per pixel. Combining a resolution cut with a moderate CRF increase usually gives the biggest reduction for the least visible quality loss.

Can I compress a video without touching the audio at all?

Yes. Leave 'Remove audio' unchecked and pick whatever audio bitrate you want to keep; the audio bitrate slider and the video CRF/resolution settings are applied independently in the same encode.

Should I export as MP4 or WebM?

MP4 (H.264) has the widest compatibility across devices, players, and editors. WebM (VP9) usually compresses somewhat smaller at an equivalent CRF and is well supported by modern browsers, so it's a good pick specifically for embedding on a web page.

Last updated: June 2026