What Is WebM? The Complete Guide to Google's Video Format

The WebM project traces its origins to 2010, when Google acquired On2 Technologies, the company behind the VP series of video codecs. At the time, the web was in the midst of the HTML5 video debate. Browser vendors disagreed over which video codec should become the standard for the new HTML5 video element. Apple pushed for H.264, Mozilla championed open formats, and there was no clear consensus.

Google saw an opportunity to break the deadlock. Shortly after acquiring On2, Google open-sourced the VP8 video codec and announced the WebM project at its Google I/O developer conference in May 2010. The goal was straightforward: create a completely open, royalty-free video format optimized for HTML5 video playback.

The initial WebM specification paired the VP8 video codec with the Vorbis audio codec inside a Matroska-based container. Google contributed the format to the open-source community under a BSD-style license, ensuring anyone could use, modify, or distribute WebM without paying royalties.

In 2013, Google introduced VP9, a major upgrade that roughly doubled the compression efficiency of VP8. VP9 became the default codec for WebM files in many contexts, and YouTube began encoding a significant portion of its library in VP9 to reduce bandwidth costs. The VP9 codec proved so effective that it saved Google billions of dollars in streaming bandwidth annually.

The most recent chapter in WebM's evolution involves AV1, a next-generation codec developed by the Alliance for Open Media, a consortium that includes Google, Mozilla, Microsoft, Apple, Amazon, Netflix, and many other technology companies. AV1 represents the future direction of WebM, offering approximately 30 percent better compression than VP9 while remaining completely royalty-free. Modern WebM files can now contain AV1 video, making the format more relevant than ever.

The video codec inside a WebM file determines how the visual data is compressed and decompressed. Each generation of WebM codecs has brought significant improvements in compression efficiency and visual quality.

VP8 was the original video codec for WebM. Released as open source by Google in 2010, VP8 delivers quality roughly comparable to H.264 Baseline Profile. It handles standard definition and 720p content well, but it struggles with higher resolutions due to its older compression algorithms. VP8 is lightweight to decode, which made it practical for the hardware available in 2010, but it has largely been superseded by VP9 for most use cases today.

VP9 is the successor to VP8 and represents a substantial leap forward. It achieves compression efficiency comparable to H.265/HEVC, meaning it can deliver the same visual quality at roughly half the bitrate of VP8. VP9 supports resolutions up to 8K, 10-bit and 12-bit color depth, high dynamic range content, and various chroma subsampling modes. YouTube relies heavily on VP9 encoding, and the codec has become the de facto standard for WebM video content. One important advantage of VP9 over H.265 is that VP9 is royalty-free, whereas H.265 involves complex and sometimes contentious licensing arrangements.

AV1 is the newest codec supported in WebM containers. Developed by the Alliance for Open Media, AV1 pushes compression efficiency even further, achieving approximately 30 percent bitrate savings over VP9 at equivalent quality. AV1 supports all the advanced features of VP9 plus additional tools like film grain synthesis, improved screen content coding, and more sophisticated prediction modes. The main drawback of AV1 is that encoding is significantly slower than VP9, though hardware acceleration support is rapidly expanding across GPUs and mobile processors.

On the audio side, WebM supports two codecs. Vorbis is the original audio codec, offering good quality at moderate bitrates. Opus is the more modern option, delivering superior quality across all bitrates and supporting both voice and music encoding. Most modern WebM files use Opus audio for its clear advantages in compression efficiency and quality.

One of WebM's greatest strengths is its broad support across modern web browsers. Google Chrome has supported WebM since its introduction in 2010, and as Chrome commands roughly two-thirds of the global browser market, this alone guarantees that WebM reaches the majority of internet users.

Mozilla Firefox added WebM support early on, as Mozilla has been a strong advocate for open web standards and royalty-free media formats. Microsoft Edge, which transitioned to the Chromium engine in 2020, now fully supports WebM playback as well. Opera, Brave, Vivaldi, and other Chromium-based browsers also support WebM natively.

Apple's Safari has historically been the notable holdout. Safari did not support VP8 or VP9 WebM playback for many years, preferring H.264 and HEVC instead. However, Safari added VP9 WebM support in Safari 16 (released in 2022), and AV1 support has been gradually rolling out across Apple's platforms. As of 2025, WebM playback works in Safari on macOS and iOS, though some older Apple devices may lack hardware decoding support for VP9 and AV1.

Beyond browsers, WebM enjoys solid support in media players like VLC, MPV, and MPC-HC. Android devices support WebM playback natively through the operating system's media framework. However, native support on older iOS devices and some smart TVs can be inconsistent, which is one reason MP4 still dominates for general-purpose video distribution.

For web developers, the broad browser support makes WebM an excellent choice for HTML5 video elements, particularly when paired with an MP4 fallback for maximum compatibility. Many video hosting platforms and content delivery networks now serve WebM as the preferred format to compatible browsers and fall back to MP4 when necessary.

WebM offers several compelling advantages that explain its popularity for web-based video.

The most significant advantage is that WebM is completely royalty-free and open source. Unlike H.264, which requires licensing fees for certain commercial uses, and H.265, which has a notoriously complex and expensive patent licensing landscape, WebM can be used by anyone for any purpose without paying royalties. This makes it particularly attractive for startups, open-source projects, and companies that distribute large volumes of video content.

Compression efficiency is another major strength. VP9 delivers quality comparable to H.265 at similar bitrates, and AV1 pushes efficiency even further. For websites and platforms that serve millions of video streams, the bandwidth savings translate directly into reduced infrastructure costs. Google has reported that VP9 encoding for YouTube saves the company significant bandwidth compared to H.264.

WebM files are generally smaller than equivalent-quality MP4 files encoded with H.264, which means faster loading times for web viewers. This is particularly important for mobile users on slower connections, where every kilobyte matters for the user experience.

The format also integrates seamlessly with modern web technologies. WebM works natively with the HTML5 video element, WebRTC for real-time communications, and the MediaSource Extensions API for adaptive streaming. This makes it a natural fit for progressive web applications, video conferencing tools, and streaming platforms.

Finally, WebM benefits from strong corporate backing. Google actively develops and promotes the format, ensuring it continues to receive improvements, optimizations, and expanded platform support. The involvement of the broader Alliance for Open Media ensures that the ecosystem around WebM and its codecs remains healthy and forward-looking.

Despite its strengths, WebM has notable limitations that prevent it from being the universal choice for all video needs.

Device compatibility remains the most significant challenge. While WebM works well in modern browsers and on Android devices, support on older hardware, smart TVs, gaming consoles, and some media players can be spotty. If you need a video that plays everywhere with zero friction, MP4 with H.264 is still the safer choice. Many set-top boxes, Blu-ray players, and older smart TVs simply do not recognize WebM files.

Professional video editing software has limited WebM support. Applications like Adobe Premiere Pro, DaVinci Resolve, and Final Cut Pro generally prefer working with MP4, MOV, or ProRes files. While you can import WebM into some editors, it is rarely the recommended workflow format. Editors working in professional production environments typically convert WebM to a more editing-friendly format before beginning their work.

Encoding speed can be a concern, particularly with newer codecs. VP9 encoding is slower than H.264 encoding, and AV1 encoding is dramatically slower still. While hardware encoding support is improving, real-time AV1 encoding remains challenging on consumer hardware. This makes WebM with AV1 less practical for live streaming or situations where encoding speed is critical.

The WebM container also has fewer features than some alternatives. The MKV container, from which WebM is derived, supports chapters, attachments, and complex track arrangements that WebM intentionally omits to keep things simple. If you need a feature-rich container with maximum flexibility, MKV or MP4 may be better choices.

Finally, while WebM's audio codecs (Vorbis and Opus) are excellent, the format does not support some popular audio codecs like AAC or AC3. This limits flexibility when you need specific audio configurations.

Understanding when to choose WebM over other formats helps you make informed decisions about your video workflow.

WebM is an excellent choice for web-based video content. If you are embedding videos on a website, serving video through a web application, or building any kind of browser-based video experience, WebM with VP9 or AV1 delivers superior compression and quality compared to H.264, reducing your bandwidth costs and improving load times for your users.

For HTML5 video elements, WebM is often the best primary format. The recommended approach is to provide a WebM source as the first option in your video element and include an MP4 fallback for older browsers. This way, the majority of visitors receive the more efficient WebM file while maintaining backward compatibility.

WebM is also ideal for WebRTC applications. Video conferencing tools, live collaboration platforms, and peer-to-peer video systems benefit from WebM's efficient codecs and native browser support.

If you are concerned about licensing and royalty costs, WebM eliminates that worry entirely. For commercial products that include video playback capabilities, using VP9 or AV1 in WebM containers avoids the patent licensing fees associated with H.264 and H.265.

However, you should avoid WebM when maximum device compatibility is required. For videos that need to play on smart TVs, gaming consoles, and older devices, MP4 remains the better choice. Similarly, if you are delivering video through social media platforms, most platforms prefer or require MP4 uploads, even if they re-encode to WebM internally.

Converting to or from WebM is straightforward with the right tools. Whether you need to convert an MP4 to WebM for web deployment or convert a WebM file to MP4 for broader compatibility, the process takes just a few steps.

ConvertFree provides a simple browser-based conversion tool that handles WebM conversions directly on your device. Since the conversion happens locally in your browser using WebAssembly technology, your video files never leave your computer, ensuring complete privacy. Simply upload your file, select the target format, and download the converted result.

When converting to WebM, you will want to consider which codec to use. VP9 is the recommended default for most situations, offering excellent compression and broad compatibility. If you need maximum compression efficiency and your target audience uses modern browsers, AV1 is the best option, though encoding will take longer.

For audio, Opus is the preferred choice over Vorbis in virtually all cases. Opus delivers better quality at every bitrate and supports a wider range of audio content types.

When converting from WebM to other formats, the most common target is MP4. This conversion is useful when you need to share a WebM video with someone whose device or software does not support the format, or when you need to upload to a platform that requires MP4. Tools like ConvertFree handle this conversion while preserving as much quality as possible.

Other common WebM conversions include WebM to AVI for legacy system compatibility, WebM to MOV for Apple editing workflows, and WebM to GIF for creating short animated clips. Each conversion scenario has its own considerations regarding quality, file size, and codec compatibility.