Why does MP4 to WebM re-encode instead of copying?

WebM is deliberately restricted to royalty-free codecs: VP8, VP9 or AV1 for video and Opus or Vorbis for audio. The H.264 and AAC inside almost every MP4 are not allowed in a WebM file, so the video and audio must be decoded and encoded again. There is no shortcut.

Which codecs does the WebM contain?

VP9 video and Opus audio, produced by your browser's own WebCodecs encoders with hardware acceleration where the device offers it.

Will the WebM be smaller than the MP4?

Often, but it depends on the Quality you choose. VP9 compresses more efficiently than H.264, so High quality usually lands near the original size with similar detail, while Medium and Low trade detail for a much smaller file. Lowering Max resolution shrinks it further.

How long does it take?

Longer than a remux, because every frame is decoded, optionally scaled and encoded again. Short clips finish quickly; long, high-resolution videos take noticeably longer, and a laptop with hardware encoding is much faster than a phone.

Where does WebM play?

Chrome, Edge, Firefox and Opera, Safari on recent macOS and iOS, Android, VLC, mpv, Discord, and Wikimedia Commons, which accepts only open formats. Older iPhones, iMovie, PowerPoint and many TVs do not open it, so keep an MP4 copy for them.

Does it work on MOV files from an iPhone?

Yes. The tool accepts .mp4, .m4v and .mov, since all three hold the same H.264 or HEVC video and are decoded the same way.

MP4 to WebM Converter — VP9 Web Video, Free

Convert MP4 to WebM

Re-encode MP4 and MOV videos as WebM with VP9 video and Opus audio for websites, Discord and open-source players. Pick a quality and size; everything runs in your browser.

No upload — runs in your browser

Batch convert & ZIP download

Free, no sign-up

Drop MP4, M4V, MOV files here

Choose files

Free: up to 5 files per batch · Files never leave your device · Paste from the clipboard works too

Private by design

Your files are processed by your own device using WebAssembly and your browser's built-in codecs. Nothing is uploaded, logged or stored.

Fast & offline-ready

No queue, no waiting for a server. Once the page has loaded it even works without a connection.

Works everywhere

Chrome, Edge, Firefox and Safari on Windows, macOS, Linux, Android and iOS. No app to install.

Why this conversion always re-encodes

Most Tinyvert video tools simply swap the container. This one cannot. WebM was created by Google in 2010 as a patent-free format for the open web, and its specification allows only VP8, VP9 and AV1 video with Opus or Vorbis audio. An MP4 almost always holds H.264 (or HEVC) and AAC, none of which may be placed in a WebM file. So every frame has to be decoded, optionally resized and encoded afresh as VP9, and the soundtrack is encoded as Opus. The result is a new generation of compression, which is why the Quality setting matters on this page in a way it does not for a remux.

When WebM is the right choice

Self-hosted video on a website. Every modern browser plays VP9 WebM, and the files are typically smaller than H.264 at the same quality, which saves bandwidth. Pair it with an MP4 fallback for older devices.
Discord and chat apps. Discord previews WebM inline, and the smaller size helps with upload limits.
Open-content platforms. Wikimedia Commons and other free-licence projects accept WebM but refuse MP4 because of H.264 patents.
Linux desktops and open-source players that ship without licensed H.264 decoders.
Replacing heavy GIFs. A short WebM loop is a fraction of the size of the same clip as a GIF; Video to GIF covers the cases that genuinely need GIF.

Quality and resolution

Setting	Options	Effect
Quality	High, Medium, Low	Trades file size against detail. High stays close to the source; Low suits previews and chat.
Max resolution	Original, 1080p, 720p, 480p, 360p	Downscales videos larger than the limit. Smaller videos are never upscaled.

Because encoding is the expensive step, the time taken scales with resolution, length and your hardware. The browser's WebCodecs encoder uses the GPU or media engine when the device has one, so a recent laptop is markedly quicker than a phone. The status line on each row shows the finished size and "re-encoded".

Supported browsers

The tool runs in Chrome, Edge, Brave and Opera on desktop and Android, Safari 17 or newer and Firefox 130 or newer. Decoding the H.264 or HEVC source relies on the codecs your browser or operating system ships, which all mainstream browsers include.

Local, private, free

The MP4 is read into memory, encoded on your device and handed back as a download; nothing is uploaded, and the page works offline after the first visit. Large files are limited by your device's memory. Five files per batch are free, and Tinyvert Pro removes that limit for a one-off US$9. Going the other way is simpler: WebM to MP4 is usually a lossless copy. If you only need a smaller MP4, Compress Video re-encodes without changing container, and Trim Video cuts the clip losslessly before you encode.

How to convert mp4 to webm — step by step

Choose a Quality (High, Medium or Low) and, if you want a smaller picture, a Max resolution such as 1080p or 720p. These settings always apply here, because WebM output is always re-encoded.
Drop up to five MP4, M4V or MOV files into the drop zone or click "Choose files". Encoding starts immediately with a progress bar per file.
When the row reports "re-encoded" and the new size, download the WebM or save the whole batch as a ZIP.

Frequently asked questions

Why does MP4 to WebM re-encode instead of copying?: WebM is deliberately restricted to royalty-free codecs: VP8, VP9 or AV1 for video and Opus or Vorbis for audio. The H.264 and AAC inside almost every MP4 are not allowed in a WebM file, so the video and audio must be decoded and encoded again. There is no shortcut.
Which codecs does the WebM contain?: VP9 video and Opus audio, produced by your browser's own WebCodecs encoders with hardware acceleration where the device offers it.
Will the WebM be smaller than the MP4?: Often, but it depends on the Quality you choose. VP9 compresses more efficiently than H.264, so High quality usually lands near the original size with similar detail, while Medium and Low trade detail for a much smaller file. Lowering Max resolution shrinks it further.
How long does it take?: Longer than a remux, because every frame is decoded, optionally scaled and encoded again. Short clips finish quickly; long, high-resolution videos take noticeably longer, and a laptop with hardware encoding is much faster than a phone.
Where does WebM play?: Chrome, Edge, Firefox and Opera, Safari on recent macOS and iOS, Android, VLC, mpv, Discord, and Wikimedia Commons, which accepts only open formats. Older iPhones, iMovie, PowerPoint and many TVs do not open it, so keep an MP4 copy for them.
Does it work on MOV files from an iPhone?: Yes. The tool accepts .mp4, .m4v and .mov, since all three hold the same H.264 or HEVC video and are decoded the same way.