MP4 to WEBM Converter
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Convert MP4 to WEBM online
Convert MP4 to WebM when you are serving video on your own website and want the smallest file. WebM is encoded with VP9 in constant-quality mode at CRF 32 with Opus audio at 128 kbps, which typically produces a noticeably smaller file than H.264 at similar visual quality.
When should you convert MP4 to WEBM?
- Serve video from your own site with a smaller download
- Use an open, royalty-free format end to end
- Provide a modern alternative alongside an MP4 fallback
- Cut bandwidth on a page with autoplaying background video
Before you convert
Encoding takes noticeably longer
VP9 is slower to encode than H.264 — expect a WebM job to take longer than an MP4 job of the same length. The payoff is at delivery, not at conversion.
Keep an MP4 fallback
Browser support for WebM is good but not universal, and outside the browser it is patchy. Serve both from a <video> element if you can.
What happens to your file
MP4 to WEBM is a full re-encode, not a container swap: the video is decoded and re-compressed with libvpx-VP9 at CRF 32, constant quality (-b:v 0), and the audio is re-encoded to Opus at 128 kbps. VP9 in constant-quality mode usually produces a noticeably smaller file than H.264 at similar visual quality, but encoding takes longer — expect WebM jobs to run slower than MP4 jobs of the same length.
Settings this conversion runs with
| Engine | ffmpeg |
|---|---|
| Video codec | libvpx-VP9 |
| Video quality | CRF 32, constant quality (-b:v 0) |
| Audio codec | Opus |
| Audio bitrate | 128 kbps |
What changes
- The MP4 picture is decoded and re-compressed with libvpx-VP9, so this is a generation loss: the output is built from an already-compressed source, not from the original camera data. Converting MP4 to WEBM and back will soften the clip a little more each time.
- Only one video and one audio stream reach the WEBM file. Additional audio languages, embedded subtitle tracks, and chapter markers are not carried across.
About MP4 and WEBM files
MP4 video
Strengths
- plays almost everywhere
- good quality-to-size
- widely supported
Limitations
- lossy compression
- less flexible than MKV
WebM video
Strengths
- small for the web
- open and royalty-free
Limitations
- limited support in some apps
- less common offline
MP4 vs WEBM
| Format | MP4 | WEBM |
|---|---|---|
| Compression | Lossy | Lossy |
| Transparency | — | — |
| Best for | streaming and sharing, playback on any device | web video, open-source playback |
Guides for this conversion
- MP4, MKV, MOV, WebM: containers vs codecs
The file extension on a video tells you the container, not how the video is compressed. Understanding the difference explains why some conversions are instant and others take minutes.
Related tools
Frequently asked questions
- Does converting MP4 to WEBM re-encode the file?
- MP4 to WEBM is a full re-encode, not a container swap: the video is decoded and re-compressed with libvpx-VP9 at CRF 32, constant quality (-b:v 0), and the audio is re-encoded to Opus at 128 kbps. VP9 in constant-quality mode usually produces a noticeably smaller file than H.264 at similar visual quality, but encoding takes longer — expect WebM jobs to run slower than MP4 jobs of the same length.
- What should you know before converting MP4 to WEBM?
- The MP4 picture is decoded and re-compressed with libvpx-VP9, so this is a generation loss: the output is built from an already-compressed source, not from the original camera data. Converting MP4 to WEBM and back will soften the clip a little more each time.
- Is this MP4 to WEBM converter free?
- Yes. You can convert MP4 to WEBM online for free, with no account and no watermark.
- Do I need to install software or sign up?
- No. Use the converter from your browser without installing software or creating an account. Files are uploaded to our servers for processing.
- Will converting MP4 to WEBM reduce quality?
- WEBM uses lossy compression, so the file can get smaller while some visual quality may change.
- Are my files safe?
- Yes. Files are processed only to complete the conversion and are auto-deleted after 2 hours. We never share them.