Solid, well-structured PR that systematically adds AV1 across all codec maps, CLI, docs, Studio, and tests. All {[key in Codec]: ...} maps have been updated. Two notable limitations to consider around container/audio codec support — see inline comments.

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Review Summary

The PR adds AV1 codec support comprehensively across the codebase. The implementation follows existing codec patterns correctly.

What's done well:

• AV1 added to all relevant codec maps: validCodecs, encoder mappings, CRF settings, media support, file extensions, and audio codec combinations
• CRF range 0-63 and default of 30 is appropriate for AV1
• Support for AV1+Opus in WebM container enables AV1+WebM output
• Even dimension validation properly included for AV1
• Test coverage includes CRF validation, dimension rounding, and file extension derivation

A few observations (non-blocking):

1. ffmpeg-args.ts - Confirm that the libaom-av1 encoder flags are correct. The aomenc encoder has specific tuning options (e.g., --cpu-used, --end-usage) that affect speed/quality tradeoff. The current implementation uses only basic CRF flag which is fine for default behavior.

2. Documentation - The docs correctly note that AV1 is unavailable on Linux ARM64 GNU, but there's no code-level enforcement of this. Users who explicitly set --codec av1 on Linux ARM64 GNU will get an FFmpeg error at render time. Consider if runtime validation would improve UX, though graceful failure is also acceptable.

3. Encoding speed - AV1 encoding with libaom-av1 is notably slow. The docs mention this, which is good. No changes needed.

Overall this is a solid implementation that correctly integrates AV1 into Remotion's codec system.

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