Ijharul Islam
A WebM file (.webm) is an open, royalty-free video format made for the web. It was introduced in 2010, is based on the Matroska container, and holds VP8, VP9 or AV1 video with Opus or Vorbis audio. Chrome, Edge, Firefox and Safari all play it, and YouTube accepts WebM uploads. Some editors, phones and players don't open it, which is when you convert it to MP4.
More on this topic: Video formats, codecs and numbers, every guide in one place.
Here's where WebM files come from, what opens them, and three ways to turn one into an MP4.
The short answer
WebM is a web video format: a Matroska-based container with VP8, VP9 or AV1 video and Opus or Vorbis audio. To open one, drag it into Chrome, Edge, Firefox or Safari, or use VLC. To convert WebM to MP4, re-encode it to H.264 and AAC: in a browser tool, in HandBrake, or with FFmpeg (ffmpeg -i in.webm -c:v libx264 -crf 20 -c:a aac out.mp4). YouTube accepts WebM directly.
Key takeaways
- WebM = Matroska-based container + VP8/VP9/AV1 video + Opus/Vorbis audio.
- Every major browser plays WebM; VLC opens it on any computer.
- Browser-based recorders save WebM when the browser can't record MP4 (Firefox, for example).
- Converting to MP4 means re-encoding to H.264 and AAC, which takes time and loses a little quality.
- YouTube and Bluesky accept WebM uploads; convert for editors and apps that don't.
What is a WebM file?
A WebM file is a video file in the WebM format, an open format designed for the web. MDN's guide to media containers describes it as based on Matroska, built entirely on free and open technologies, and introduced in 2010. A compliant WebM player must support VP8 and VP9 video and Vorbis and Opus audio; AV1 video is also used.
| WebM | MP4 | |
|---|---|---|
| Container based on | Matroska | ISO base media file format (from QuickTime) |
| Usual video codec | VP9 (also VP8, AV1) | H.264 (also H.265, AV1) |
| Usual audio codec | Opus (also Vorbis) | AAC (also MP3, Opus) |
| Royalty-free | Yes | Depends on the codecs |
| Browser playback | Chrome, Edge, Firefox, Safari | All browsers |
| Phones, TVs, editors | Mixed | Nearly universal |
| Extension and MIME type | .webm, video/webm | .mp4, video/mp4 |
WebM is used heavily behind the scenes: many websites serve WebM video to browsers, and browser-based recording tools save WebM because browsers can encode it natively.
Why is my recording saved as WebM?
Your recording is saved as WebM because the browser recorded it, and some browsers can only record WebM. Web pages record with the browser's built-in MediaRecorder, which saves whatever formats that browser supports. Chrome, Edge and Safari can record MP4; Firefox records WebM.
QuickVeed's free screen recorder, webcam recorder and voice recorder all check first and save MP4 (or M4A for audio) where your browser can, and WebM otherwise. They tell you which format you'll get before you start. If you need MP4 and you're in Firefox, record in Chrome, Edge or Safari instead, or convert afterwards.
How do you open a WebM file?
You open a WebM file in a web browser or in VLC. Either works on Windows, Mac, Linux and ChromeOS:
| Device | How to open it |
|---|---|
| Any computer | Drag the file into a Chrome, Edge, Firefox or Safari window, or open it in VLC (free) |
| Windows | VLC, or a browser; built-in players vary by Windows version |
| Mac | Safari or VLC; QuickTime Player may not open it |
| iPhone and iPad | Safari can play it from a web page; for files, use the VLC app or convert to MP4 |
| Android | Chrome, VLC or most gallery apps |
| Video editors | Some import WebM, others don't; convert to MP4 if yours refuses it |
If the video plays without sound, the audio is probably Opus or Vorbis and the player lacks that codec; VLC plays both.
How do you convert WebM to MP4?
You convert WebM to MP4 by re-encoding the video to H.264 and the audio to AAC. Three ways:
In your browser
Open the WebM in the free video compressor in Chrome, Edge or Safari, which can record MP4. Pick Light to keep up to 1080p (about 23 MB a minute). The tool plays the video once and records a new MP4, so a 5-minute video takes about 5 minutes. It's free, runs in your browser and never uploads your file, for files up to 500 MB and 10 minutes. The video trimmer works the same way if you also want to cut the start or end.
HandBrake (free app)
Open the WebM, choose a preset such as Fast 1080p30 (MP4, H.264, AAC), and click Start Encode. Good for long recordings and batches.
FFmpeg (command line)
ffmpeg -i in.webm -c:v libx264 -crf 20 -preset medium -c:a aac -b:a 160k out.mp4. CRF 18 to 23 is the normal quality range; lower is better and larger. Screen recordings from browsers sometimes have a variable frame rate; add -r 30 to get a steady 30 fps file that editors handle better.
Why not just rename .webm to .mp4? Because the codecs inside are still VP9 and Opus; many players will refuse the file or play it without sound. Remuxing without re-encoding (-c copy) can technically put VP9 and Opus in an MP4, but compatibility is poor, so re-encode for anything you'll share.
Can you upload WebM to YouTube and social media?
You can upload WebM to YouTube, which lists WebM among its supported file formats, and to Bluesky, whose launch post listed WebM alongside MP4, MPEG and MOV. For most other platforms, and for anything you send to other people, convert to MP4 first:
| Destination | WebM OK? |
|---|---|
| YouTube | Yes |
| Bluesky | Yes |
| Instagram, TikTok, Facebook | Convert to MP4 |
| X (Twitter) | Convert to MP4 (H.264 recommended) |
| Email, WhatsApp, clients | Convert to MP4 |
| Website <video> | Yes, ideally with an MP4 fallback |
For which codec to choose when you convert, see H.264 vs H.265; for the other common container question, MKV vs MP4.
Is WebM better than a GIF?
For short looping clips on a website, yes: a WebM is usually a small fraction of the size of the same clip as a GIF, with full colour instead of GIF's 256-colour palette, and it can carry sound. That's why many sites that look like they show GIFs actually serve short muted WebM or MP4 videos set to loop. The catch is where you can post them: chat apps, email and many forums still expect a real GIF file.
| WebM (VP9) | GIF | |
|---|---|---|
| Colours | Millions | 256 per frame |
| Sound | Yes | No |
| File size for the same clip | Small | Many times larger |
| Plays in | Browsers and video players | Almost everywhere, including email and chat |
If you need a GIF anyway, the free video to GIF converter makes one from a WebM or MP4 and keeps it small; how to convert a video to GIF has the settings.
Is WebM good quality?
Yes. WebM's quality depends on the codec and bitrate, not the format: VP9 and AV1 are modern, efficient codecs, comparable to or better than H.264 at the same bitrate. A WebM screen recording looks just as sharp as an MP4 at the same settings. The reason to convert is compatibility, not quality, and each conversion loses a little, so keep the original WebM until you're happy with the MP4.
Want a still from a WebM? The free frame extractor opens WebM directly in your browser and saves any frame as an image.
Frequently asked questions
What is a WebM file?
An open web video format based on Matroska, with VP8, VP9 or AV1 video and Opus or Vorbis audio.
How do I open a WebM file on Windows?
Drag it into Chrome, Edge or Firefox, or open it with VLC.
Can an iPhone play WebM?
Safari can play WebM on web pages; for a downloaded file, use the VLC app or convert it to MP4.
Is WebM better than MP4?
Not better, just different. WebM is royalty-free and efficient; MP4 with H.264 plays on more devices and editors.
Does converting WebM to MP4 lose quality?
A little, because it re-encodes. Use a high-quality setting and convert from the original.
Why does my screen recorder save WebM?
Browser-based recorders save the formats the browser supports. Firefox records WebM; Chrome, Edge and Safari can record MP4.
Try it with your own video
Upload your recordings and add captions, translations or a voiceover. Upload an MP4 or MOV, check the transcript, and export captions. QuickVeed plans start at $18/month, and new accounts get a 14-day trial with 250 credits, no card needed. Sign up or see pricing.
Sources
Competitor details in this post were checked against these public pages in October 2026. Products and prices change, so confirm with each vendor before you decide.
