Convert MP4 to WebM

WebM on a web page

WebM was made for the web: an open format with no license fees, played by Chrome, Edge and Firefox. A common pattern is to offer a page's video twice, in a video element that lists the WebM source first and the MP4 after it. Browsers that play WebM take it; the rest fall back to the MP4. So keep your MP4s and add WebM beside them, with the same names so the pairs are easy to match.

For background and hero videos, turn the Keep the sound switch off in More settings. Browsers generally autoplay video only when it is muted, so a sound track there is dead weight, and leaving it out makes the file smaller. Set Size to 720p or 1080p while you are there: a background rarely needs 4K. For the still image a page shows before the video starts, the Video Editor's Save this frame makes a PNG of any moment.

VP9, AV1 or VP8

The figures are the bit rates Octoolo aims for with each codec. VP9 is the safe choice for WebM. AV1 makes the smallest files, and recent NVIDIA, AMD and Intel graphics cards can encode it; older browsers and devices cannot play it. VP8 is there for very old players, and since it needs more bits than VP9 for the same look, pick it only when a player asks for it.

The first time you ask for AV1, Octoolo tries each AV1 encoder it knows on your PC, graphics card first, and keeps using the first one that works. If none of the card's does, the processor encoder takes over, which is slower but gives the same kind of file.

Why VP9 takes longer

Octoolo makes VP9 on the processor, with Google's libvpx encoder, so it takes longer than an MP4 export on a graphics card. At High it uses libvpx's careful mode for the most detail; Balanced and Small switch to its real-time mode, which is much quicker and a little softer. Octoolo converts one video at a time while doing this, and you can watch the speed and the remaining time on each file's line.

If the MP4 already holds VP9 or AV1 video, which some do, As it is copies the picture into the WebM without encoding it at all, and only the sound is made again.

Before a long batch, convert one typical file at Balanced and look at it in a browser. If it looks right, run the rest the same way; if you see softness in fine detail, go up to High for the batch.

Sound, subtitles and size

• Sound becomes Opus, at 192 kbps for High, 128 for Balanced and 64 for Small. Vorbis is under Sound codec for older players. Every sound track in the MP4 is kept.
• Subtitles stored as text in the MP4 become WebVTT, the subtitle format of the web.
• Size brings a 4K or 1080p video down to 720p or less for the page, and Octoolo never scales a video up.
• Frames a second can drop a 60 fps screen capture to 30, which halves the frames to encode.
• Quality: High is never needlessly bigger than the MP4, Balanced aims at about half the size, and Small suits thumbnails and previews.

Looking for a looping animation rather than a video? MP4 to GIF also makes animated WebP pictures, which are a different thing from WebM video.