How to convert WebM to MP4 with ffmpeg (Windows and Mac)

Recorded a video in your browser and it came out as WebM? That happens on older browsers or some setups, and it can be a problem: not every app and social network handles that format well. In this tutorial you will learn to convert WebM to MP4 with ffmpeg, the free, open-source tool video professionals use.

WebM vs MP4: what is the difference?

Editor de Vídeo Online records MP4 on current browsers. If your video comes out as WebM, the first thing to do is update Chrome or Edge. If that does not help, convert it as shown below.

Step 1: install ffmpeg

Windows

Open Command Prompt or PowerShell and run:

winget install ffmpeg

Close and reopen the terminal so the command is recognized.

Mac

With Homebrew installed, run in Terminal:

brew install ffmpeg

Check the installation

ffmpeg -version

If you see the version, you are ready.

Step 2: convert the video

Go to the video's folder (for example cd Downloads) and run:

ffmpeg -i video.webm -c:v libx264 -pix_fmt yuv420p -r 30 video.mp4

What each part does:

• -i video.webm: the input file.
• -c:v libx264: encodes the video as H.264, the most compatible standard.
• -pix_fmt yuv420p: a color format every player and platform accepts.
• -r 30: locks 30 frames per second, avoiding timing glitches.
• video.mp4: the output file name.

Step 3 (optional): tune quality and size

To control quality, add -crf (lower means better quality and a bigger file; 18 to 23 is a good range):

ffmpeg -i video.webm -c:v libx264 -crf 20 -preset slow -pix_fmt yuv420p -r 30 video.mp4

If the video has audio, convert the audio to AAC too:

ffmpeg -i video.webm -c:v libx264 -pix_fmt yuv420p -r 30 -c:a aac -b:a 160k video.mp4

Converting many files at once

On Mac or Linux:

for f in *.webm; do ffmpeg -i "$f" -c:v libx264 -pix_fmt yuv420p -r 30 "${f%.webm}.mp4"; done

On Windows (PowerShell):

Get-ChildItem *.webm | ForEach-Object { ffmpeg -i $_.Name -c:v libx264 -pix_fmt yuv420p -r 30 ($_.BaseName + ".mp4") }

If you produce lots of hand-drawing videos, consider Editor de Vídeo Online's advanced version, which already renders MP4 in batches: see how to batch-generate videos with Python.

Common problems

• "ffmpeg is not recognized": close and reopen the terminal after installing.
• No sound: the original video may have no audio. Animations recorded in Editor de Vídeo Online are silent; add narration and music afterwards (see how).
• Stuttering video: use -r 30 to lock the frame rate and see performance tips for recording in the browser.

Frequently asked questions

Does converting WebM to MP4 lose quality?

There is a re-encode, but with -crf between 18 and 20 the difference is invisible.

Is there an online converter?

There are, but you have to upload your video to a server. ffmpeg converts on your computer, with no size limit and without exposing the file.

Why did my video come out as WebM?

Older browsers cannot record MP4 natively. Updating Chrome or Edge usually fixes it.

Conclusion

A single ffmpeg command turns any WebM into an MP4 that works everywhere. But update your browser first: in most cases Editor de Vídeo Online already delivers MP4 directly.