MP4 to WebM Converter (VP9 / AV1)
Convert MP4 to WebM for your website. ProMedia re-encodes the video to VP9, or AV1 if you pick it, and the audio to Opus: the royalty-free pair every modern browser streams natively. Encoding runs in your browser through WebCodecs, so the MP4 is never uploaded, and there is no size cap or watermark.
- Runs on your device
- WebCodecs · GPU
- Works offline
Updated
Drop your videos here
How to convert MP4 to WebM
Step 1: Drop your MP4 videos on the box above.
Step 2: Pick Quality: Balanced for most pages, Best quality for a hero video, Faster for drafts.
Step 3: Optional: under Advanced settings choose AV1 for smaller files, or set Audio to No audio for a silent loop.
Step 4: Press Convert and download the WebM files.
Good to know
Settings explained
- Quality
- Only used when a stream has to be re-encoded. Compatible streams are copied with no quality loss.
- Faster: Smaller file, quickest export
- Balanced: Good quality at a sensible size
- Best quality: Largest file, slowest export
- Video codec
- Automatic copies the original video stream when the new format can hold it, so there is no quality loss.
- Automatic: Best codec the format and your device support
- H.264 (AVC): Plays everywhere
- H.265 (HEVC): About 35% smaller, newer devices
- VP9: Web / WebM
- AV1: Smallest files, slowest to encode
- Always re-encode
- Off: compatible streams are copied instantly and losslessly. On: every stream is re-encoded, which can fix playback glitches.
Formats
Batch-friendly: add many files and they are processed one after another — if one fails, the rest still finish.
How it runs
- Hardware video engine
- Video is decoded and encoded by your device’s media hardware through WebCodecs — usually several times faster than real time.
MP4 vs WebM: which is better quality?
At the same bitrate, VP9 and AV1 in a WebM look better than H.264 in an MP4; at the same look, they need fewer bits. MP4 remains the more compatible download, which is why many sites serve WebM first and keep MP4 as a fallback.
| Feature | MP4 (H.264) | WebM (VP9) | WebM (AV1) |
|---|---|---|---|
| Bits for the same picture | Baseline | About 35% fewer | About 50% fewer |
| Encoding speed here | Fast; hardware on most devices | Fast with a hardware VP9 encoder, slower in software | Slowest; needs a recent browser |
| Plays in | Everything | Chrome, Edge, Firefox and recent Safari | Recent browsers and newer devices |
| Audio | AAC | Opus | Opus |
What is a WebM file?
A WebM file is a web-first video container: a restricted form of Matroska that only allows VP8, VP9 or AV1 video and Opus or Vorbis audio, all free of licence fees. HTML5 players, background loops and many web apps use it because every major browser decodes it without plug-ins.
Why use WebM for websites
- Lighter pages. A VP9 background video needs roughly a third fewer bytes than the same H.264 clip, so it starts sooner on slow connections.
- Silent loops. Set Audio to No audio for autoplaying hero videos; browsers usually allow autoplay only when a video is muted, so the audio track is wasted bytes.
- Easy fallback. List the WebM first and the original MP4 second in your
<video>element, and every browser picks a file it can play.
Can I convert MP4 to WebM with a transparent background?
No. H.264 video in an MP4 has no alpha channel, so there is no transparency to carry over into the WebM. A transparent WebM has to be exported that way from the animation or editing app that made it.
Tips & troubleshooting
Keep the MP4 as well: browsers that cannot play your WebM fall back to it, so neither file is wasted.
For a page background, cut it to the best few seconds with the video trimmer and set Resolution to 720p; few loops need more.
Need a WebM back as MP4 later? Use WebM to MP4.
Want an animated image instead of a video element? The animated WebP maker turns clips into WebP animations.
MP4 to WebM Converter FAQ
How do I convert MP4 to WebM without losing quality?
A WebM conversion always re-encodes, because MP4 files rarely contain VP9 or AV1 that could be copied. Choose Best quality, keep the original resolution and, if your visitors use recent browsers, pick AV1, which keeps more detail per byte. The change from the source is then hard to see.
Is WebM smaller than MP4?
Usually, at the same visual quality. Not always, though: browser VP9 encoders have a quality floor, so a small, heavily compressed MP4 can come out larger as WebM. The estimate under the options shows the expected size before you press Convert.
Will WebM play on iPhone?
Recent Safari versions play VP9 WebM, but older iPhones and many apps do not. On a website, keep an MP4 source as a fallback. To send a video to a person, MP4 is the better file.
Is encoding VP9 slow?
It depends on the device. With a hardware VP9 encoder it is quick; without one, the browser encodes in software, which can take longer than the clip lasts. If the browser cannot encode VP9 at all, ProMedia uses VP8 instead and notes it in the log.
Is your video uploaded anywhere?
No. Your video is processed by your own browser on your own device. There is no server that receives files, so nothing is uploaded, stored or shared. You can even switch to airplane mode once the page has loaded.