Example: soundtrack generated from the rendered video #398

Disclosure: I work on Sonilo (licensed video-to-music), so this proposal involves our product.

revideo's <Audio/> support assumes the user brings a finished track. For the automated-pipeline use case the docs lead with, that's the one asset code can't easily produce: every rendered variation needs music that fits its own timing, and issues like #373 show people wrestling with the audio layer today.

The idea is an example, not a core change: render a scene, send the MP4 to a music API that generates a track from the video itself, then mux it in (or feed it back through <Audio/>). Length matches the render automatically, and every track is licensed and safe for commercial use (terms apply). I'd write it to match the structure in midrender/examples, docs included.

Recipe for the general pattern: https://github.com/cindyxu1030/sonilo-video-to-music-cookbook

Worth an example slot? Happy to open the PR if so.