Convert MP4 to WebM Online
Convert MP4 to WebM using open-source VP8/VP9 codecs — optimized for the modern web
.mp4 · up to 100 MB
Free conversion
MP4 to WebM in the browser
Total privacy
The video is processed with FFmpeg.wasm locally. No MP4 file ever leaves your device.
Open codecs
VP8 and VP9 are royalty-free. WebM is the open standard for HTML5 video.
Web-ready
The resulting WebM is compatible with modern Chrome, Firefox, Edge, and Safari.
No installation
FFmpeg.wasm runs directly in the browser. No software installation required.
How it works
Three steps, no hassle
Upload your MP4 file
Select or drag any MP4 file with H.264 video and AAC audio. The file is processed locally and never uploaded to any server.
Choose VP8 or VP9 quality
Select the target codec: VP8 for maximum compatibility with older browsers, VP9 for 30-50% better compression at the same visual quality level.
Download the WebM file
FFmpeg.wasm converts the file in your browser. Download the resulting WebM, ready to embed in HTML5 using the <video> tag.
FAQ
Got questions?
VP8 was the original codec introduced by Google in 2010 after acquiring On2 Technologies. It offers compression comparable to H.264 and has universal support across all modern browsers. VP9, released in 2013, improves compression efficiency by 30-50% over VP8 at the same visual quality level, and is the format YouTube uses for most of its 4K videos. AV1 is the next generation, developed by the Alliance for Open Media (AOMedia) consortium with contributions from Google, Mozilla, Microsoft, Apple, and Amazon; it offers 30% better compression than VP9 but requires hardware decoding to avoid performance impact. For current web projects, VP9 offers the best balance between compatibility and efficiency.
At equal bitrates, VP9 produces slightly superior or comparable visual quality to H.264. The perception of 'worse quality' with WebM is usually due to conversions with inadequate bitrate settings, not the codec itself. For web content, a WebM with VP9 at CRF 33 typically produces visually indistinguishable results from an equivalent H.264 MP4 at the same bitrate, often in a smaller file size. Quality is ultimately determined by encoding settings, not the container format.
Chrome, Firefox, Opera, and Chromium-based Edge support WebM with VP8, VP9, and AV1 natively. Safari on macOS and iOS has supported WebM/VP8 since Safari 14.1 (2021) and VP9 since Safari 14 on macOS Big Sur, but AV1 only on Apple Silicon devices. Internet Explorer does not support WebM. For maximum compatibility, serve both MP4 (H.264) and WebM (VP9) using multiple sources in the <video> tag: WebM first for compatible browsers, MP4 as fallback.
Google acquired On2 Technologies in 2010 and open-sourced VP8 under the BSD license, creating the WebM format alongside the Matroska container. The primary motivation was eliminating royalties associated with H.264 (patented by MPEG LA), which could reach $0.20 per device. YouTube progressively migrated to VP9 to reduce bandwidth costs: at the same visual quality, VP9 videos are 35-40% smaller than H.264 equivalents, which at the scale of billions of views represents enormous infrastructure savings annually.
Size reduction depends on the codec and settings. With VP8 at the same perceptual quality as H.264, the size is similar or even up to 10% larger in some cases. With VP9, the typical reduction is 25-40% compared to equivalent H.264. With AV1, it can reach 40-50%. However, conversion is not magic: if the original MP4 is already heavily compressed, re-encoding to WebM may actually increase the size if quality settings are too conservative. The key is adjusting the CRF (Constant Rate Factor) appropriately.
For VP9, CRF mode (quality-driven variable bitrate) is recommended with values between 28 and 40: CRF 28 for high quality, CRF 33 for balance, CRF 40 for minimum acceptable size. In FFmpeg: -c:v libvpx-vp9 -crf 33 -b:v 0. The -b:v 0 enables pure CRF mode, which is more efficient than constrained quality mode. For streaming, Google recommends targets of 1 Mbps for 720p, 1.8 Mbps for 1080p, and 4.5 Mbps for 4K with VP9.
WebM, VP8, and VP9: history, technical advantages, and use in the modern web
The WebM format was born in May 2010 when Google completed its acquisition of On2 Technologies (initiated in August 2009 for $106 million) and released the VP8 codec as open source under the BSD license. Google presented it at Google I/O 2010 alongside Mozilla and Opera as a royalty-free alternative to the dominant H.264. The WebM container is a subset of the Matroska (MKV) format, adapted for web use: it supports VP8, VP9, or AV1 video, Vorbis or Opus audio, and WebVTT subtitles. The motivation behind WebM was purely economic and strategic: the MPEG LA consortium charged royalties for H.264 that could affect the open distribution of video on the web. By open-sourcing VP8, Google removed that barrier for any developer or company wanting to distribute video without paying licensing fees. VP9, VP8's successor, was developed internally at Google between 2011 and 2013, and YouTube began using it massively from 2014. The efficiency of VP9 over VP8 is substantial: at equal visual quality, VP9 files are 30-50% smaller, which at YouTube's scale represents millions of dollars in monthly bandwidth savings. In 2015, Google co-founded the Alliance for Open Media alongside Amazon, Cisco, Intel, Microsoft, Mozilla, and Netflix to develop AV1, VP9's successor, which achieved even higher compression ratios while maintaining the royalty-free philosophy.
From a technical perspective, choosing between VP8, VP9, H.264, and H.265 for web distribution involves multiple factors. H.264 (AVC, Advanced Video Coding) remains the most universal codec: any device manufactured since 2010 decodes it in hardware. Its weakness is efficiency: it was designed in 2003 and its compression algorithm is less sophisticated than its successors. VP9 outperformed H.264 in compression efficiency by approximately 35-45% according to multiple independent studies, and YouTube reported bandwidth reductions of up to 35% when migrating from H.264 to VP9 for 4K content. H.265 (HEVC) offers similar efficiency to VP9 but carries a complex licensing problem: multiple patent consortiums (MPEG LA, HEVC Advance, Velos Media) charge royalties independently, which slowed its adoption. AV1 surpasses VP9 by an additional 20-30% in compression but requires 5-10x more CPU power for real-time encoding, though hardware decoding is now available in recent Intel (11th gen), AMD (RDNA2), and Apple Silicon (M1 onwards) processors. For the 2024-2025 web, the optimal strategy is to serve AV1 to supporting browsers, VP9 as the second tier, and H.264 as the universal fallback.
To convert MP4 to WebM with FFmpeg, the basic VP9 command is: ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 33 -b:v 0 -c:a libopus -b:a 128k output.webm. The -crf 33 parameter defines quality (scale 0-63, lower values = higher quality), and -b:v 0 activates pure CRF mode without bitrate cap. For VP8: ffmpeg -i input.mp4 -c:v libvpx -crf 10 -b:v 1M -c:a libvorbis output.webm, where VP8's CRF scale runs from 4 (maximum quality) to 63 (minimum). For fast encoding with multiple threads: add -threads 4 (or the number of available CPU cores). For two-pass encoding (better quality): first pass with -pass 1 -an -f null /dev/null, second with -pass 2. Opus audio is superior to Vorbis in modern WebM: Opus delivers better quality at 96 kbps than Vorbis at 128 kbps, and has universal support in all WebM-compatible browsers. For HTML5 embedding, the recommended practice is: <video><source src='video.webm' type='video/webm'><source src='video.mp4' type='video/mp4'></video>, ensuring full compatibility even in older Safari.