WebM to MP4 Converter — Free, No Upload
Move a WebM into MP4 by trying stream copying first and falling back to H.264 video and AAC audio encoding when needed. Processing time and quality changes therefore depend on the input codecs and which path succeeds.
- Runs in your browser
- Nothing is uploaded
- No signup; device limits apply
Lower is better quality and a bigger file. Ignored when streams can be copied.
How to use this tool
Select the WebM and the quality setting for re-encoding. That setting is not used on the copy path, so an unchanged output size after changing quality does not imply that every run performs a new encode.
Results and examples
Play the MP4 in the actual destination player and verify picture and sound. The filename extension alone does not guarantee device compatibility, and a fallback encode can alter fine detail relative to the source.
Worked example
Convert a browser-recorded WebM to MP4 and test both picture and sound on the recipient’s phone. For files requiring re-encoding, compare quality 18 and 28; the setting has no effect when stream copy succeeds.
Limitations
- Compatible streams are copied and failures trigger H.264/AAC re-encoding, so the path varies by file.
- An MP4 extension alone does not guarantee playback in every device.
Fields
| Field | Guidance and constraints |
|---|---|
| Quality if re-encoding is needed | Lower is better quality and a bigger file. Ignored when streams can be copied. · Accepted range: 18–32 · Input step: 1 |
Data handling
Processing stays in the current browser tab; the site does not upload tool input for the calculation itself.
Sources
Frequently asked questions
Why does changing quality leave size unchanged?
The compatible stream-copy path does not use re-encoding quality.
Is conversion always lossless?
No. The fallback re-encode can introduce generation loss.
Related tools
You do not need to start over. Continue with the tool that fits your next step.
