What Is WebM? Google's Open Video Format for the Web
WebM is an open, royalty-free video format developed by Google specifically for the web. Released in 2010, it was designed to provide high-quality video compression without the patent licensing fees associated with formats like H.264. WebM files use VP8 or VP9 video codecs paired with Vorbis or Opus audio, all wrapped in a container based on the Matroska (MKV) format.
How WebM Works Under the Hood
WebM is a subset of the Matroska multimedia container, restricted to specific codec combinations optimized for web delivery. The container itself is lightweight and uses a binary format based on EBML (Extensible Binary Meta Language), which provides efficient parsing and minimal overhead.
The video component uses either VP8 or VP9 codecs, both developed by Google and released under royalty-free licenses. VP8, the original codec, delivers quality roughly comparable to H.264 Baseline profile. VP9, released in 2013, offers significantly improved compression efficiency, achieving quality similar to H.265/HEVC at comparable bitrates while remaining completely free to use.
For audio, WebM supports Vorbis and Opus codecs. Opus in particular is considered one of the best audio codecs available, excelling at both speech and music across a wide range of bitrates from 6 kbps to 510 kbps. The combination of VP9 video and Opus audio represents the current best practice for WebM encoding.
Why Choose WebM: Benefits and Drawbacks
WebM was created to solve specific problems with web video distribution. Here are its key strengths and weaknesses.
- Completely royalty-free: no licensing fees for encoding, decoding, or distributing WebM content
- VP9 delivers compression efficiency comparable to H.265 without patent complications
- Opus audio codec provides excellent quality at lower bitrates than AAC
- Native support in Chrome, Firefox, Edge, and Opera browsers
- Optimized specifically for web streaming with low-latency playback capabilities
- Open-source reference implementations available for all codecs
- Limited support on Apple devices: Safari only added VP9/WebM support in macOS Big Sur and iOS 14
- Hardware decoding for VP9 is less widespread than H.264, increasing battery usage on mobile devices
- Smaller ecosystem of editing and authoring tools compared to MP4
- Not commonly used for offline video distribution or physical media
WebM vs MP4: Which Format for Your Website?
Choosing between WebM and MP4 depends on your priorities: openness and compression versus universal compatibility.
| Feature | WebM | MP4 |
|---|---|---|
| Licensing | Completely royalty-free | H.264 patents (free for web use) |
| Browser support | Chrome, Firefox, Edge, Opera; limited Safari | All browsers including Safari |
| Compression (VP9 vs H.264) | 30-50% smaller at same quality | Larger files, but hardware-optimized |
| Mobile support | Android native; iOS limited | Universal on iOS and Android |
| Encoding speed | VP9 encoding is significantly slower | H.264 encoding is fast with hardware support |
| Social media | Not accepted by most platforms | Accepted everywhere |
Common WebM Playback Issues and Solutions
WebM video not playing in Safari
Ensure you are using macOS Big Sur (11.0) or later and iOS 14+. For older Apple devices, provide an MP4 fallback using the HTML5 <source> element with multiple formats.
VP9 video stuttering on mobile
The device may lack VP9 hardware decoding. Reduce the resolution or bitrate, or switch to VP8 which has broader hardware support. Alternatively, serve MP4 to mobile users.
No audio in WebM file
Verify the audio track uses Vorbis or Opus codec. Some encoders may produce WebM files with incompatible audio. Re-encode the audio track using Opus for best results.
WebM file not seekable in browser
The file may be missing cues (seek index). Re-mux the file with a tool that writes WebM cues, or ensure your encoder generates cue points during encoding.
Large WebM file despite VP9 encoding
Check your encoding settings. VP9 requires a two-pass encode or CRF mode for optimal compression. Single-pass CBR encoding produces larger files. Use CRF 31 as a starting point.
How to Convert Video to WebM
- 1
Choose your source file
Select any video file to convert. Common sources include MP4, AVI, MOV, and MKV files. WebM conversion works with virtually any video format.
- 2
Select codec and quality
Choose VP9 for best compression or VP8 for faster encoding. For audio, Opus is recommended over Vorbis for superior quality at low bitrates.
- 3
Upload and process
Upload your video to WeLoveConvert for browser-based conversion. Your files stay on your device since processing happens locally.
- 4
Download and test
Download the converted WebM file and test it in your target browsers. Consider providing an MP4 fallback for maximum compatibility.
Frequently Asked Questions
Is WebM better than MP4?
WebM with VP9 offers better compression than MP4 with H.264, producing smaller files at the same quality. However, MP4 has broader device compatibility. For web-only distribution where Chrome and Firefox are the primary targets, WebM can be the better choice. For universal playback, MP4 remains safer.
Can I play WebM on iPhone?
WebM playback on iPhone requires iOS 14 or later for VP9 support in Safari. Older iOS versions cannot play WebM files natively. If you need to support older iPhones, provide an MP4 fallback alongside your WebM files.
Why did Google create WebM?
Google created WebM to provide a high-quality, royalty-free video format for the open web. The H.264 codec used in MP4 requires patent licensing, which Google saw as a barrier to an open internet. By releasing VP8 and VP9 under royalty-free licenses, Google aimed to make video accessible without licensing costs.
What is the difference between VP8 and VP9?
VP9 is the successor to VP8, offering approximately 50% better compression efficiency. VP9 supports higher resolutions up to 8K, 10-bit and 12-bit color depth, and features like spatial and temporal scalability. VP8 is simpler and faster to encode but produces larger files.
Does WebM support transparency?
Yes, WebM with VP9 supports alpha channel transparency, making it one of the few video formats that can display transparent video in web browsers. This feature is useful for animated overlays, lower thirds, and compositing effects in web applications.
Is WebM good for YouTube uploads?
YouTube accepts WebM uploads and will re-encode them for delivery. However, uploading in the highest quality source format is recommended regardless. YouTube internally uses VP9 for much of its playback, so uploading a high-quality WebM preserves quality through fewer transcoding steps.
What replaced WebM?
WebM has not been replaced. Google continues to develop the format, and the AV1 codec (developed by the Alliance for Open Media, which Google co-founded) is being integrated into WebM as the next-generation video codec, succeeding VP9.
Can WebM contain subtitles?
Yes, since WebM is based on the Matroska container, it can embed WebVTT subtitle tracks. This makes it possible to include captions directly in the video file for web playback without requiring separate subtitle files.
WebM represents Google's vision for open, royalty-free web video. With VP9 delivering compression efficiency rivaling proprietary codecs and Opus providing top-tier audio quality, WebM is an excellent choice for web-focused video distribution. While MP4 remains the safe default for universal compatibility, WebM's technical advantages and zero licensing costs make it particularly attractive for high-volume web publishers and developers committed to open standards.