Convert MP4 to WebM (VP9 and Opus)
WebM is the open format of the web: it uses the VP9 codec for video and Opus for audio. It is supported by all modern browsers and by many sites and tools. VP9 compresses better than H.264, but encoding is slower.
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The lower the number, the better the picture. 31 is the value Google recommends for 1080p.
VP9 is slow. Higher values are faster at the cost of a slightly larger file.
How to use it
- Install ffmpeg if you haven't already.
- Open a terminal in the folder containing your file.
- Copy the generated command, adjust the file names if needed, then run it.
- Open the resulting file to check the result.
When should you use WebM?
To embed a video in a web page with a good quality-to-size ratio, for stickers or animated backgrounds, or when a service explicitly asks for WebM. For ordinary sharing (messaging, email), prefer MP4.
Quality and size
A VP9 video at CRF 30 is generally 30 to 50% smaller than H.264 at comparable visual quality. The gain is most visible at high resolutions.
Frequently asked questions
Why "-b:v 0" with CRF?
For VP9, CRF alone is capped by a default bitrate. Adding "-b:v 0" removes that cap and lets quality decide the bitrate: it's the recommended mode.
Is WebM better than MP4?
For the web, it offers better compression, but it is less widely supported outside browsers: editing software, iPhone, TVs. For maximum compatibility, stick with MP4.
Why is encoding so slow?
The VP9 codec is much more demanding than H.264. The "-row-mt 1" option uses all of your processor's cores and already speeds things up.
Can I get AV1 instead of VP9?
Yes, with the libaom-av1 or SVT-AV1 encoder if your version of ffmpeg includes them, but encoding is even slower. VP9 remains the best compromise for everyday use.