Summary

The client-side rendering limitations page states:

Firefox does not support encoding AAC audio via WebCodecs. When rendering in Firefox, use Opus audio (WebM container) instead of AAC (MP4 container).

Mediabunny now offers an optional @mediabunny/aac-encoder package (installable via remotion add — see packages/cli/src/extra-packages.ts). @remotion/web-renderer already calls ensureAacEncoderRegistered() from register-aac-encoder.ts, which registers that encoder when native AAC encoding is unavailable.

Why this issue

• The limitation may be overstated for users who have @mediabunny/aac-encoder installed: AAC in MP4 might work in Firefox after registration.
• Related API docs still say Firefox only returns ["opus"] for getEncodableAudioCodecs() — see the note in get-encodable-audio-codecs.mdx — but getEncodableAudioCodecs in code runs ensureAacEncoderRegistered() first, so behavior may not match the docs.

Suggested work

1. Verify in Firefox (with and without @mediabunny/aac-encoder) whether MP4 + AAC client-side / web rendering works as expected.
2. Update packages/docs/docs/client-side-rendering/limitations.mdx to distinguish native WebCodecs vs. optional Mediabunny encoder, and document when Opus/WebM is still required.
3. Align packages/docs/docs/web-renderer/get-encodable-audio-codecs.mdx (and any similar mentions) with actual runtime behavior after ensureAacEncoderRegistered().
4. Optionally cross-link from the limitations section to Mediabunny formats / version docs if we document the AAC encoder extension there.

Labels

documentation / web-renderer as appropriate.