feat(demuxer): add async iteration and demuxAsync method

[Brooooooklyn]

Add for await...of loop support and demuxAsync() method to all demuxers (Mp4Demuxer, WebMDemuxer, MkvDemuxer).

Changes:

• Implement AsyncGenerator trait via NAPI-RS for all demuxers
• Add read_next_chunk() method for single-packet reading
• Add demuxAsync() as awaitable alternative to sync demux()
• Add DemuxerChunk type with discriminated union pattern
• Update TypeScript types with declaration merging for Symbol.asyncIterator
• Add 10 tests covering async iteration and demuxAsync

The async iterator provides a cleaner streaming API:

  for await (const chunk of demuxer) {
    if (chunk.chunkType === 'video') {
      videoDecoder.decode(chunk.videoChunk!)
    }
  }

The demuxAsync() method eliminates the polling pattern:

  // Before
  while (demuxer.state !== 'ended') {
    demuxer.demux(100)
    await new Promise(r => setTimeout(r, 1))
  }

After

  await demuxer.demuxAsync()

---

Note

Introduces an async, stream-friendly demuxing API and awaitable demux calls.

• Async iteration: Implemented [Symbol.asyncIterator] on Mp4Demuxer, WebMDemuxer, MkvDemuxer via #[napi(async_iterator)], yielding DemuxerChunk from new DemuxerInner::read_next_chunk()
• Awaitable demux: Added demuxAsync(count?) to all demuxers (awaitable version of demux())
• TypeScript updates: Declared DemuxerChunk and iterator signatures; enhanced JSDoc on demuxers in index.d.ts/dts-header.d.ts
• Benchmarks: Replaced polling loops with await demuxer.demuxAsync()
• Tests: Added async iterator and demuxAsync coverage for MP4/WebM/MKV, including audio+video paths
• Build: Bumped napi feature to napi5 in Cargo.toml

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[Brooooooklyn]

• feat(demuxer): add async iteration and demuxAsync method #17 👈 (View in Graphite)
• main

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[Copilot]

Pull request overview

This PR adds async iteration support and a demuxAsync() method to all three demuxers (Mp4Demuxer, WebMDemuxer, MkvDemuxer), providing a more idiomatic JavaScript API for consuming demuxed chunks.

Key changes:

• Implements AsyncGenerator trait for all demuxers to enable for await...of loops
• Adds demuxAsync() method as an awaitable alternative to the existing synchronous demux() method
• Introduces DemuxerChunk type with discriminated union pattern for yielding video/audio chunks

Reviewed changes

Copilot reviewed 9 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/webcodecs/demuxer_base.rs	Adds DemuxerChunk struct and read_next_chunk() method for single-packet async iteration
src/webcodecs/mp4_demuxer.rs	Implements AsyncGenerator trait and demuxAsync() method for Mp4Demuxer
src/webcodecs/webm_demuxer.rs	Implements AsyncGenerator trait and demuxAsync() method for WebMDemuxer
src/webcodecs/mkv_demuxer.rs	Implements AsyncGenerator trait and demuxAsync() method for MkvDemuxer
src/webcodecs/mod.rs	Exports the new DemuxerChunk type
Cargo.toml	Updates napi feature from napi4 to napi5 to support async iterators
dts-header.d.ts	Adds TypeScript types for DemuxerChunk and async iterator interfaces using declaration merging
index.d.ts	Generated TypeScript definitions including new async methods and documentation
test/demuxer.spec.ts	Adds 10 comprehensive tests covering async iteration and demuxAsync for all demuxers
benchmark/bench-napi.ts	Updates benchmark to use simplified demuxAsync() API
benchmark/bench-polyfill.ts	Updates benchmark to use simplified demuxAsync() API

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