Free MP4 to WebM Converter: Video for Websites

To convert MP4 to WebM, re-encode the video with an open WebM codec such as VP8 or VP9 and put it in a WebM container. With the AREM Labs MP4 to WebM Converter you drop the MP4 into the page, pick a quality level, press Convert and download a VP8 WebM with Vorbis audio, all inside your browser.

WebM is mostly a web format. People convert to it when they want a looping hero video on a landing page, a product demo inside a help center, or a lighter clip in a web app, and they want an open, royalty-free format that Chrome, Firefox and Edge play natively. It is not the right delivery format for every destination, so this guide covers both the conversion and where the WebM file should, and should not, go. For the broader picture of containers and codecs, start with the pillar guide on how to convert video files for any device or platform.

Free toolMP4 to WebM ConverterConvert MP4 videos to WebM format directly in your browser. Adjust resolution and quality without uploading files to remote servers or losing your privacy.Open the tool

How to convert MP4 to WebM step by step

These steps use the MP4 to WebM Converter. The video engine runs in your browser tab through WebAssembly, so the footage stays on your computer.

1. Drag your file onto the “Drop your MP4 file here” area or click it to choose one. A single file of up to 1 GB is accepted.
2. Check the preview player to confirm you loaded the right clip.
3. Under “Quality (CRF)”, pick High (18), Balanced (23), Small (28) or Smallest (32). Lower numbers keep more detail.
4. Confirm that “Output format” shows “WebM (VP8) - small for the web”.
5. Press Convert. The first run downloads the video engine once, about 30 MB, and then shows a processing percentage.
6. Play the result in the preview, compare its size with the source size, and press Download.

Two details of the current version are worth knowing before you judge the output. The encoder uses VP8 in a fast real-time mode, which keeps browser encoding times reasonable but compresses less efficiently than slower VP9 encoders. The video bitrate is also capped at roughly 1 Mbps, and the output is scaled to a width of 1,280 pixels with the aspect ratio kept. For a background or demo clip on a web page that is a sensible size; for detailed 4K footage it is not.

Free toolMP4 to WebM ConverterConvert MP4 videos to WebM format directly in your browser. Adjust resolution and quality without uploading files to remote servers or losing your privacy.Open the tool

MP4 vs WebM: which format goes where?

The simple rule: WebM for your own web pages, MP4 for everything you upload to someone else’s platform.

Question	MP4 (H.264 + AAC)	WebM from this tool (VP8 + Vorbis)
Licensing	Patent-licensed codecs	Open and royalty-free
Chrome, Firefox, Edge	Plays	Plays
Safari and iPhone	Plays everywhere	Recent versions play WebM; older devices may not
Social platforms and marketplaces	Widely accepted	Often rejected; check the upload help page
Transparency (alpha)	Not supported	Format supports it, but an MP4 source has none to keep
Best use	Uploads, sharing, downloads	Self-hosted video on your own site
Size at similar visual quality	Baseline	Similar with VP8; VP9 is usually smaller

That last row matters. Many people expect WebM to be dramatically smaller than MP4. With VP8 the gain is modest, and sometimes the WebM is the same size or larger. Convert, compare the two sizes the tool shows, and keep whichever serves your page better.

How to use the WebM file on your website

Because some Apple devices still struggle with WebM, the safe pattern is to serve WebM first and MP4 as a fallback. Browsers pick the first source they can play:

<video autoplay muted loop playsinline poster="hero.jpg">
  <source src="hero.webm" type="video/webm">
  <source src="hero.mp4" type="video/mp4">
</video>

A few practical notes for background and hero videos:

• Autoplay usually only works when the video is muted, so there is no need for an audio track. Remove it in an editor if you want to save a little more space.
• Keep loops short, typically under 15 seconds, so the file stays light on mobile data.
• Crop out anything the layout will hide. If your page shows the video in a wide banner, trim the top and bottom with the Video Cropper before converting, so you do not spend bytes on pixels nobody sees.
• If the MP4 fallback itself is heavy, shrink it with the Video Compressor, which can target a size in megabytes.

On Shopify or WooCommerce product pages, the video you upload through the product media uploader is a different case: those uploaders expect common formats such as MP4, so upload the MP4 and reserve WebM for theme sections or custom code you control. When unsure, check your platform’s current media help page for accepted formats.

Going the other way

If someone sends you a WebM screen recording and you need it in an email, a marketplace listing or an iPhone, you need the reverse conversion. The WebM to MP4 Converter handles that, and the guide on converting WebM to MP4 locally in the browser explains the settings. Matroska files follow the same logic; see the article on MKV to MP4 conversion.

Common mistakes

• Replacing the MP4 on your site with WebM only, which leaves some Safari and older iPhone visitors with a blank player; keep both files and list WebM first, MP4 second.
• Uploading the WebM to a marketplace or social platform, which often gets rejected or re-encoded badly; upload MP4 there and use WebM only on pages you host.
• Choosing High (18) and expecting a sharper result on detailed 4K footage, which the 1 Mbps cap and 1,280-pixel width will not deliver; use this tool for web-sized clips and keep high-resolution masters in MP4.
• Converting a clip that already came from a WebM back and forth, which stacks compression artifacts; always convert from the best original you have.
• Expecting a transparent background after conversion, which does not happen because H.264 MP4 carries no alpha channel; export transparency from your editing or animation software instead.

Frequently asked questions

Is WebM smaller than MP4? Not always; a VP8 WebM is often similar in size to an H.264 MP4 at comparable quality. VP9 WebM files are usually smaller, but they take much longer to encode, especially in a browser.

Does WebM work on iPhone? Recent iPhone and Safari versions can play WebM, but older devices may not. Keep an MP4 fallback on your website so every visitor sees the video.

Is my video uploaded when I convert MP4 to WebM? No, the conversion happens entirely in your browser tab. Only the video engine is downloaded once; your file never leaves your device.

What audio codec does the WebM use? The converter writes Vorbis audio, the standard pairing for VP8 video in WebM. If the video will autoplay muted on a web page, you can drop the audio track entirely to save space.

Convert once, serve two formats

WebM is a good fit for video you host yourself, as long as an MP4 fallback sits right behind it. Convert the clip in the MP4 to WebM Converter, compare the two file sizes, and publish whichever combination loads fastest for your visitors.