How to Open a WebM File
- Any computer: drag the file into a Chrome, Firefox or Edge window. The browser plays it.
- Windows, Mac, Linux: VLC media player plays WebM, including VP9 and AV1 video.
- Mac: QuickTime Player does not open WebM files; use a browser or VLC.
- Android: the built-in player and Chrome play WebM.
- iPhone and iPad: support depends on the iOS version. If a file does not play, use the VLC app or convert it to MP4.
To edit a WebM file or play it on a TV, converting it to MP4 is usually the easiest fix.
WebM: An Open Container for the Web
WebM is a multimedia container format designed for the web. It was released by Google in May 2010 as part of the WebM Project, an initiative to establish open, royalty-free video standards for HTML5. The format is based on the Matroska container (the same technology behind MKV files), adapted specifically for web delivery.
WebM files contain video encoded with VP8, VP9, or AV1 codecs and audio encoded with Vorbis or Opus. All of these codecs are open-source and royalty-free, which means anyone can encode, decode, and distribute WebM content without paying patent licensing fees.
Key point: WebM is a container, not a codec. It is the packaging that holds the actual video and audio data. The quality is determined by the codec inside (VP8, VP9, or AV1), not by the WebM container itself.
The History of WebM
WebM's story begins with On2 Technologies, a video codec company that developed the VP series of codecs. Google acquired On2 in February 2010 for $124.6 million, primarily for the VP8 codec. In May 2010, Google open-sourced VP8 under a BSD-style license and announced the WebM format at the Google I/O conference.
The timing was strategic. In 2010, the HTML5 <video> tag was being standardized, but the web had no royalty-free video codec that all browser vendors could agree on. H.264 was patent-encumbered through MPEG LA, making it impossible for free and open-source software to include it without licensing concerns. Google positioned WebM as the open alternative.
Chrome and Firefox adopted WebM support immediately. Opera followed. Microsoft's Internet Explorer and Apple's Safari held out, continuing to support only H.264. The "codec war" of 2010-2015 shaped the web video landscape we have today — and ultimately led to Google developing VP9 (2013) and co-developing AV1 (2018) with the Alliance for Open Media.
Codecs Inside WebM
A WebM file can contain one of three video codecs and one of two audio codecs:
| Codec | Type | Released | Key Feature |
|---|---|---|---|
| VP8 | Video | 2010 | First WebM codec; comparable to H.264 Baseline |
| VP9 | Video | 2013 | ~30% smaller than H.264 at same quality; used by YouTube for 4K |
| AV1 | Video | 2018 | ~30% smaller than VP9; next-generation open codec |
| Vorbis | Audio | 2000 | Open-source lossy audio; paired with VP8 |
| Opus | Audio | 2012 | Efficient from 6 to 510 kbps; strong at low bitrates |
VP9 is the most widely used video codec in WebM files today. YouTube adopted VP9 in 2014 and uses it for much of its streaming, including 4K, alongside H.264 and AV1. VP9 achieves approximately 30% better compression than H.264 at the same perceived quality, which translates to significant bandwidth savings at YouTube's scale.
AV1 is the newest generation, developed collaboratively by the Alliance for Open Media (AOM) — a consortium that includes Google, Mozilla, Microsoft, Apple, Amazon, Netflix, and others. AV1 improves on VP9 by another ~30%, but encoding is significantly slower. Browser support for AV1 in WebM is growing rapidly, with Chrome 70+, Firefox 67+, and Edge 79+ all supporting it.
Opus is a modern open audio codec. In public listening tests it has matched or beaten AAC, MP3 and Vorbis at the bitrates tested, especially low ones. Opus handles everything from low-bitrate speech (6 kbps) to high-fidelity music (510 kbps) with a single codec, making it ideal for web video.
Where WebM Is Used
WebM has become deeply embedded in the web ecosystem:
- YouTube: streams much of its video as VP9, and increasingly AV1. 4K playback in Chrome or Firefox uses one of these two open codecs.
- Wikipedia / Wikimedia Commons: requires WebM (or Ogg) for all video uploads. MP4 is explicitly not allowed due to patent licensing concerns.
- WebRTC: the real-time standard behind browser video calls requires VP8 and H.264 support, and VP9 and AV1 are widely used. Calls travel over RTP rather than in WebM files, but browser recordings are usually saved as WebM.
- Reddit / Imgur: many “GIFs” on Reddit, Imgur and similar sites are actually short silent MP4 or WebM videos, which are far smaller than real animated GIFs.
- HTML5 <video>: WebM is a first-class format for the HTML5 video element, supported natively by Chrome, Firefox, Edge, and Opera since their earliest versions.
- MediaRecorder API: when web applications record video through the browser (screen recording, webcam capture), most browsers default to the WebM format.
Scale perspective: YouTube said in 2017 that people watch over 1 billion hours of its video per day, and much of it is streamed with VP9. That makes VP9 one of the most-watched video codecs.
Browser & Device Support
WebM support varies by browser and device:
| Platform | WebM VP9 Support | Notes |
|---|---|---|
| Chrome | Full | Since Chrome 29 (2013) |
| Firefox | Full | Since Firefox 28 (2014) |
| Edge | Full | Since Edge 79 (Chromium-based, 2020) |
| Opera | Full | Since Opera 16 (2013) |
| Safari (macOS) | Full | Recent versions; older versions may not play WebM |
| Safari (iOS) | Full | Recent iOS versions; older ones may need an app such as VLC |
| Android | Full | Since Android 4.4 (VP8 since 2.3) |
| Smart TVs | Partial | YouTube app uses VP9; native playback varies by manufacturer |
| VLC Player | Full | Cross-platform, bundles VP8/VP9/AV1 decoders |
As of 2026, WebM VP9 is supported by 97%+ of web browsers globally (source: Can I Use). The last major holdout was Safari, which added WebM support in later versions. For web developers, WebM is now a safe default format for HTML5 video.
Technical Structure of WebM Files
WebM is a profile (subset) of the Matroska container format. Matroska (MKV) is a very flexible, open-source container that supports virtually any codec combination. WebM restricts this flexibility to a specific set of open codecs:
- EBML Header: the first element in every WebM file, identifying it as a Matroska-based document with the WebM DocType. This is analogous to the
ftypatom in MP4. - Segment: the root element containing all media data, organized into clusters.
- Tracks: metadata describing each track — video resolution, frame rate, codec ID, audio sample rate, and channel count.
- Clusters: groups of encoded video and audio frames with timestamps. Each cluster typically holds 1–5 seconds of media.
- Cues: a seek index for random access, similar to the
moovatom's sample tables in MP4.
WebM files can be configured for streaming by placing the Cues element before the Clusters (analogous to faststart in MP4). This enables the browser to seek within the video without downloading the entire file first.
How to Convert WebM to MP4 or MP4 to WebM
- MP4 to WebM (the converter above): VP9 video at CRF 30 and Opus audio at 128 kbps. The FFmpeg equivalent is
ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 30 -b:v 0 -row-mt 1 -cpu-used 3 -pix_fmt yuv420p -c:a libopus -b:a 128k output.webm. - WebM to MP4: re-encode to H.264 and AAC for devices without WebM support. Our WebM to MP4 converter uses these settings:
ffmpeg -i input.webm -c:v libx264 -crf 23 -preset medium -pix_fmt yuv420p -c:a aac -b:a 192k -movflags +faststart output.mp4.
Both directions re-encode the video, because WebM and MP4 normally carry different codecs. Keep the original if you may need it later.