Video to WebM

Video to WebM - Online Video Format Converter — WebM is an open video format led by Google, derived from a streamlined Matroska container and paired with the fully royalty-free VP9/Opus codecs, making it ideal for web playback and video-site uploads. Supports format conversion, lossless remuxing, compression, scaling, looping, and resizing — all processed locally in your browser, with files never uploaded to a server. A built-in metadata / tag editor reads the source video's tags (title, artist, album, album artist, date, genre, track, comment), lets you edit them, and writes them into the output — including the no-re-encode copy mode, where quality is perfectly preserved.
Supported input: Videos using open royalty-free codecs such as VP8/VP9/AV1/MPEG-4/FFV1 (WebM, MKV, MP4, MOV, AVI containers). Everything is converted locally in your browser; files are never uploaded to a server.
First use loads an ~30MB video processing engine into the current browser. It is cached and reused afterwards, so please be patient.
🎥
Click to select or drag and drop a video file
Supports WebM, MKV, MP4, MOV, AVI and other common formats; under 500MB recommended
Format Convert: Pick a codec combination and click the button below to remux/re-encode the video as WebM. If the input codec is WebM-compatible, choose "No re-encode" for instant remuxing (no quality loss).
Video Compress: Re-encodes the video to WebM with the chosen quality or target bitrate to produce a smaller file. This mode requires re-encoding, so "No re-encode" is unavailable.
Video Scale: Scales the video to a preset resolution and outputs WebM. This mode requires re-encoding, so "No re-encode" is unavailable.
Video Loop: Repeats the video content N times and outputs WebM. Combined with "No re-encode" this completes almost instantly.
Video Resize: Scales the video by percentage or explicit width/height pixels and outputs WebM. This mode requires re-encoding, so "No re-encode" is unavailable.
What is WebM? The royalty-free web video pairing

WebM is a container — technically a strict profile of Matroska — that Google opened in 2010 to give HTML5 <video> a fully royalty-free option: VP8 or VP9 video plus Vorbis or Opus audio, nothing else allowed. The motivation was licensing. H.264 and HEVC ship with patent pools that browser vendors and site publishers must pay for; the VP family and AV1 were released under irrevocable royalty-free licenses, so a WebM file can be encoded, distributed and played by anyone with zero legal exposure. That is why this site's converters lean on VP8/VP9 — the freedom travels with the codec, not the container.

Five facts to anchor the rest of the page:
• WebM = Matroska profile: same EBML structure, codec whitelist (VP8/VP9/AV1 + Vorbis/Opus)
• every WebM file is a valid MKV; not every MKV qualifies as WebM
• VP8 (2010, from Google's On2 acquisition) ≈ H.264-class; VP9 (2013) roughly halves VP8's bitrate; AV1 (2018) cuts roughly a third more
• Opus is the modern audio half: better quality per bit than MP3/AAC at every bitrate
• supported natively by Chrome, Firefox, Edge, Opera and Android; Safari support arrived late (macOS 14+/iOS 17.4+ era)
VP8, VP9, AV1: one family, three generations

All three codecs come from the same lineage (On2's VPx series, then the Alliance for Open Media). VP8 was the launch codec of WebM in 2010 — competitive with H.264 of its day, and still the fastest to encode of the family. VP9 landed in 2013 and roughly halves the bitrate VP8 needs for the same visual quality; it powered YouTube's 4K rollout for years. AV1 (2018, by the AOMedia consortium of Amazon, Apple, Google, Microsoft, Netflix and others) targets roughly 30% further savings over VP9 — and is patent-encumbered only in the "free to everyone" direction. Encoding cost climbs with each generation: AV1 is dramatically slower to encode than VP8, which is exactly why this page offers the older, faster codecs for browser-side conversion.

WebM and MKV: subset and superset

WebM did not invent a new container — it restricted an existing one. A WebM file uses Matroska's EBML structure with a whitelist: video must be VP8/VP9/AV1, audio must be Vorbis/Opus, and features like attachments or exotic tracks are excluded. The consequence is pleasant: every WebM is a playable MKV, so converting WebM to MKV is a trivial remux, while MKV to WebM is only possible when the codecs inside are already on the whitelist — otherwise a re-encode is unavoidable. Think of WebM as "MKV that a browser can be promised to decode."

Opus and Vorbis, the audio half

Vorbis (2002, Xiph.Org) was the open answer to MP3 and is still fully supported. Opus (2012, RFC 6716) superseded it: a single codec that handles speech and music, switches intelligently between them, and beats MP3 and AAC on quality per bit at essentially every bitrate — all royalty-free. For new WebM files the choice is settled: Opus, unless an ancient device demands Vorbis.

Common misconceptions
  • "WebM is a codec." It is a container profile. The codec inside is VP8/VP9/AV1 — saying "convert to WebM codec" conflates the box with what is in it.
  • "VP9 is free, so everyone uses it." Royalty-free does not mean universal: hardware decode support and corporate encoder pipelines lag for years, which is why H.264 still dominates delivery despite its licenses.
  • "WebM only plays in Chrome." All evergreen browsers and Android support it; only older Safari releases were the holdout, and even Apple added WebM playback in recent versions.
  • "MKV to WebM is a quick remux like MP4 to MKV." Only when the codecs are already VP8/VP9/AV1 + Vorbis/Opus. An H.264-in-MKV file must re-encode to become WebM.

Related tools: Video to MKV for the full Matroska container, Video to MP4 for the ISO-BMFF/H.264 world, Video to OGG/FLAC for the audio side of the Xiph family, and Video to WebP/APNG for short animation without a video codec at all.