Convert WebM to MP4
Turn WebM files from browser screen recorders and some meeting tools into MP4 that opens on iPhone and in video editors.
Settings
How to use
- 1
Add videos
Drop MP4, MOV, WebM, MKV and similar files. Several videos can be converted in turn with the same settings.
- 2
Choose the output format
MP4 (H.264), WebM (VP9), MOV or MKV. When the codec already matches, the stream is copied instead of re-encoded, which is very fast.
- 3
Convert and save
Save once the progress bar reaches 100%. Long videos take a while; keep the tab open.
Why WebM will not open
WebM is Google's web-oriented video format using VP8 / VP9 video and Opus audio. Browsers play it, but the iPhone Photos app, most video editors and TVs do not.
MP4 (H.264 + AAC) plays on virtually every device and program. VP9 to H.264 requires re-encoding, so the time taken scales with the video length.
Frequently asked questions
Is quality lost?
It is re-encoded, so it changes slightly according to the Quality setting. At "High" or above the difference is negligible.
Why does the converted video have no audio?
The screen recording may have been made without microphone or system audio. If the WebM has an audio track it is converted to AAC and included.
Can I convert a WebM whose length shows as 0 or invalid?
Yes. WebM produced by the browser MediaRecorder API often lacks duration metadata. This tool reads the whole file to determine the length, so it converts fine.
Why can't I convert in Firefox?
Firefox supports WebCodecs from version 130 on desktop. On older versions or Android, use Chrome or Edge.
Help us improve the service
If a conversion fails, sending us the circumstances helps us track down the cause. Knowing which devices and formats fail most often, and how long processing takes, lets us revise the supported formats and fix the bugs behind them. If you don't mind, leaving this on is a real help.
What is sent
- The tool you used and the settings you chose (output format, quality, etc.)
- Your device specs (GPU, memory, core count)
- The input format with a rough size
- How many files succeeded or failed and how long it took
- The error type and details when something fails
What is never sent
- The files themselves and file names
- Text, subtitles or prompts you add to a video
- The text to be read aloud, voice descriptions, the pronunciation dictionary and saved voices
- The text in PDFs, the text you rewrote or redacted, passwords, font names and the page ranges you enter
- IP addresses
The data goes only to this site's own server, never to a third-party service.
Details sent by specific tools (counts, times, kinds and yes/no only)
In addition to “What is sent”, text to speech and the PDF tools send the following details.
- Text to speech
- The approximate number of characters and sentences, how many parts the text was generated in, and how long the AI model took to load.
- PDF tools (all)
- The page count range, whether editing is restricted, whether a permissions password was entered, and whether the PDF is signed or encrypted.
- PDF text editing and redaction
- The numbers of rewrites, deletions, white-outs and redactions, the number of rewritten characters by source (original font or fallback font, the latter as a range) and the fallback typeface, the kinds of reasons why lines cannot be edited, and the number of pages turned into images by redaction and the reasons.
- PDF page operations and conversion between images and PDF
- The numbers of inputs and outputs, of pages rotated, deleted, duplicated or moved, of images inserted as they are, converted, in HEIC format or with corrected orientation, and of pages rendered at a lower resolution (all as ranges), whether the original was updated in place or a new document was created, and whether the original protection was reapplied, form fields were written into the page and bookmarks were added back.
- PDF compression
- The numbers of inputs and outputs, of images downsized, not downsized and black-and-white, of downsized images whose transparency was also downsized, that stayed lossless or that were converted from CMYK to RGB, and how many times the file was compressed (all as ranges), the kinds of reasons images were not downsized, whether the target size was met and the kind of reason it was not met, the range of how much smaller the file got, whether the original protection was reapplied, and whether the original PDF was returned unchanged.
- PDF cropping and page numbers
- The numbers of inputs and outputs and of pages cropped, numbered or with their margins reduced (all as ranges), how the margins were set, how the pages to crop or number were chosen, the number format and position, the range of the starting number, that the original was updated in place, and whether the original protection was reapplied.