For AI agents
If you are an AI agent (Claude Code, Codex, Cursor or similar) and the person wants a video for their project with Opus Motion, read the guide first and follow it: https://opusmotion.com/agents.md.
- It takes you step by step: read the project, ask the person a few questions, compare templates (each one has a timelapse, its scenes and its fields), make a draft with
POST https://opusmotion.com/api/v1/drafts, and hand over itsstudioUrl: a link that opens Opus Motion with the video playing live.PATCHwith the draft'seditTokenchanges it, and the link stays the same. - Plain HTTPS and JSON: no key, no account, no MCP. Nothing is rendered; the person exports the MP4 from the studio.
- Never drive this site with a browser to fill the studio: use the API. If it refuses, tell the person and stop.
- More: llms.txt · this page in Markdown · developer docs · OpenAPI
WebM to MP4 that plays everywhere
For screen and camera recordings made in a browser and other VP8 or VP9 videos. Re-encoded to H.264 and AAC on your device. Free, no sign-up.
Your file never leaves your device: the tool runs inside your browser. Up to 1 GB. Use it at https://opusmotion.com/tools/webm-to-mp4.
How to use it
- Drop the WebM, or tap the box to pick it.
- The converter re-encodes VP8 or VP9 to H.264 and Opus or Vorbis to AAC, on your device.
- Download the MP4, or put the clip in a launch template.
The first time, your browser downloads the video engine (31 MB, once); after that it opens from the cache.
About WebM files
WebM is the web's open video format: VP8, VP9 or AV1 video with Opus or Vorbis sound. Many screen and camera recorders that run in a browser save WebM, and so do some sites you download videos from.
Those codecs don't play in every MP4 player, so a WebM is always re-encoded here: to H.264 video and AAC sound, the pair that plays on phones, computers, editors and social apps.
Re-encoding happens on your device. It takes longer than a copy, and longer on a phone than on a computer; the bar shows how far along it is.
WebM files recorded in a browser often don't store their total length, so some players can't show a duration or let you skip ahead. The MP4 has both. AV1 WebMs can't be read here yet.
Questions
Why does a WebM have to be re-encoded?
Because MP4 players expect H.264 (or HEVC) video and AAC sound, and a WebM holds VP8 or VP9 with Opus or Vorbis. The picture has to be encoded again in the codec players read.
How long does it take?
About as long as encoding a video takes on your device: a short screen recording takes seconds on a recent computer, a long one or a phone takes longer. Nothing leaves your device while it works.
My WebM shows no duration. Will the MP4?
Yes. Recordings made in a browser often leave the length out of the WebM, which breaks the time bar in some players. The MP4 is written with its full length and plays and seeks normally.
Does it work with AV1 WebMs?
Not yet: the video engine this tool uses can't read AV1. VP8 and VP9 WebMs, the most common, work.
Is my video uploaded anywhere?
No. The conversion runs inside your browser, with ffmpeg compiled to WebAssembly. Your file is read where it is and never sent to a server. The first time, your browser downloads the video engine (31 MB, once); after that it opens from the cache.
What's the largest file it takes?
Up to 1 GB when the video is copied. When it needs re-encoding: up to 500 MB and 2 minutes on a computer, or 200 MB and 1 minute on a phone or low-memory device. The limit is decided after reading the codecs. The MP4 is kept in your browser's memory until you download it, so a phone, which has less memory, may not manage a very large file: if one fails there, try it on a computer.
More free tools
- Video converter: Any video to MP4: MOV, WebM, MKV, AVI and more, copied without re-encoding when it can be
- MOV to MP4: iPhone videos, Mac screen recordings and QuickTime files to MP4, usually in seconds
- MKV to MP4: OBS and other MKV recordings to MP4, remuxed in seconds when they hold H.264
- All free tools