MP4 to WebM Converter (Free, No Upload, No Signup)

Convert any MP4 file to WebM right in your browser. Nothing gets uploaded to a server. WebM is the format web developers reach for when they want small, browser-native video without royalty headaches. The conversion runs locally using FFmpeg compiled for your browser, so your files stay on your device from start to finish.

Try it in your browser

Loading FFmpeg engine... (~31 MB)

How to mp4 to webm converter online

1Drop your MP4 file into the tool above, or click to browse your files.
2Choose your quality setting. Higher quality means a larger file. The default works well for most web use.
3Click convert and download your WebM file. The conversion happens in your browser and nothing is uploaded.

About WEBM format

WebM was created by Google and released in 2010 as an open alternative to H.264. The goal was a royalty-free format that browsers could support without licensing fees. It uses VP8 or VP9 for video and Vorbis or Opus for audio, all open codecs developed by the open-source community.

For web developers, WebM matters because it loads fast and plays natively in most modern browsers without plugins or player libraries. Background videos, landing page demos, and embedded clips often use WebM to reduce page weight compared to MP4.

The tradeoff is encoding speed. VP9 takes longer to encode than H.264 at equivalent quality, which is why this converter may take a moment on larger files. The result is worth it for files you're going to serve to thousands of users. The smaller file size adds up in bandwidth savings.

If you're preparing video for a website and need broad compatibility, the standard approach is to use WebM as the primary source and MP4 as a fallback inside a video element, so Safari and older browsers can still play it.

Use the API

curl -X POST https://renderio.dev/api/v1/run-ffmpeg-command \
  -H "X-API-KEY: ffsk_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
  "ffmpeg_command": "-i {{in_video}} -c:v libvpx-vp9 -crf 31 -b:v 0 -c:a libopus {{out_video}}",
  "input_files": {
    "in_video": "https://example.com/input.mp4"
  },
  "output_files": {
    "out_video": "output.webm"
  }
}'

Need an API key? Get your free API key to start processing files programmatically.

Common Variations

VP9 with Opus audio (best for web, default)

-i input.mp4 -c:v libvpx-vp9 -crf 31 -b:v 0 -c:a libopus output.webm

VP8 with Vorbis audio (older browser compat)

-i input.mp4 -c:v libvpx -crf 10 -b:v 1M -c:a libvorbis output.webm

VP9 high quality (lower CRF = better quality)

-i input.mp4 -c:v libvpx-vp9 -crf 20 -b:v 0 -c:a libopus -b:a 128k output.webm

VP9 two-pass for exact bitrate target

ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:v 1M -pass 1 -an -f null /dev/null && ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:v 1M -pass 2 -c:a libopus output.webm

Small file (lower resolution, higher CRF)

-i input.mp4 -c:v libvpx-vp9 -crf 40 -b:v 0 -vf scale=640:-1 -c:a libopus output.webm

No audio (video only)

-i input.mp4 -c:v libvpx-vp9 -crf 31 -b:v 0 -an output.webm

Frequently Asked Questions

Is this really free?+

Yes, free with no catch. No account, no trial, no file size limits tied to a paywall. The converter runs in your browser, so there are no server costs for us either.

Do my files get uploaded anywhere?+

No. The conversion runs entirely in your browser using a local version of FFmpeg. Your MP4 file never leaves your device. It doesn't touch our servers or anyone else's.

What is WebM and why would I use it?+

WebM is an open video format built for the web. It uses VP8 or VP9 video codecs with Vorbis or Opus audio. It's royalty-free, plays natively in Chrome, Firefox, Edge, and Opera, and produces smaller files than H.264 MP4 at the same visual quality. Web developers use it for background videos, demos, and anywhere they want fast-loading browser-native video.

What is VP8 vs VP9? Which should I choose?+

VP9 is newer and gives about 50% better compression than VP8 at the same quality: smaller files, same video. Choose VP9 unless you need to support very old browsers (pre-2014). If you're targeting Safari on older iOS, check compatibility first since WebM support on Safari arrived late.

Does Safari support WebM?+

Safari added WebM support in version 16 (2022). For iPhones and Macs running recent iOS/macOS, it works. Older Safari versions don't support it. If broad Safari compatibility matters, you might want to offer both MP4 and WebM versions of your video, with MP4 as fallback inside a video tag.

Will the quality be lower than my original MP4?+

It depends on the CRF setting. CRF 31 (the default) gives good quality that most people can't distinguish from the original on a normal screen. Lower CRF values (like 20) give higher quality at larger file size. The conversion is lossy either way, but so is most web video delivery.

How big will the WebM file be compared to the MP4?+

VP9 typically produces files 30-40% smaller than H.264 MP4 at equivalent visual quality. So a 10MB MP4 might become a 6-7MB WebM at matching quality. If you need an even smaller file, increase the CRF value or reduce the resolution using the small file preset.

Can I convert in bulk or automate this?+

The browser tool handles one file at a time. If you need to convert dozens or hundreds of files, the RenderIO API lets you send MP4-to-WebM commands over HTTP and process them in parallel. You get a download URL for each result without running anything locally.

Privacy

Your video file is processed entirely in your browser using a local copy of FFmpeg. It is never uploaded to any server, and no one at RenderIO or anywhere else can see your file. The tool collects no data about your video, your device, or your usage.

Related Operations

Need to process at scale?

Automate this with the RenderIO FFmpeg API. Process thousands of files programmatically or through no-code video automation.

Get your API key