Export MP4 and WebM

H.264/AAC MP4

Choose mp4-h264-aac for the broadest delivery compatibility. Aelion probes an exact AVC configuration and runs the AAC runtime canary during preflight. API availability alone is not proof that the selected resolution, rate, profile, level, and audio settings can encode.

AV1/AAC and HEVC/AAC MP4

mp4-av1-aac and mp4-hevc-aac are explicit opt-in profiles. They remain visible in the API even when unsupported so products can present deterministic alternatives. Never silently relabel or transcode an unsupported choice as H.264.

VP9/Opus WebM

Choose webm-vp9-opus for an open web stack. Preflight checks both the requested VP9 video config and Opus audio path.

Bitrate and dimensions

Start with a product preset based on pixel count, frame rate, motion, content, and delivery constraints, then let users trade quality for size. Do not infer support from bitrate alone. Preflight the exact width, height, frame rate, bitrate, channel layout, color contract, and materials.

4K boundaries

4K is a capability result, not a universal promise. GPU texture limits, encoder limits, memory, storage, and thermal behavior all matter. Offer a lower-resolution fallback when exact preflight does not pass.

Long output and resume

Write long files to OPFS or another seekable sink. exportResumableMuxed() checkpoints committed segments under an application job ID and resumes only uncommitted units. A normal session.export.startProfile() job is intentionally one-shot.

Memory output

For short exports, finalize a memory sink, create a Blob with the reported MIME type, trigger a download, revoke the object URL, and release the byte buffer as soon as the product no longer needs it. See Export jobs and sinks.