OfflineAudioContext Incremental Rendering

[gabrielsanbrito]

This PR proposes changes to the Web Audio spec to enable rendering audio from OfflineAudioContexts in chunks.

Github issue: #2445
Feature explainer: https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/OfflineAudioContext/explainer.md

---

💥 Error: 422 Unprocessable Entity 💥

PR Preview failed to build. (Last tried on Jun 11, 2026, 10:20 PM UTC).

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Error output:

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[gabrielsanbrito]

@hoch @padenot @mjwilson-google, this is the first draft for OfflineAudioContext incremental rendering. PTAL when you have some time.

While writing this, we had some open questions that might be better to discuss here:

• In this draft I am proposing using Infinity to denote the undefined-length render scenario. However, OfflineAudioContextOptions.length is currently an unsigned long, which cannot be Infinity. What would be preferrable?
  • Swap all Infinity usage for null; or
  • Convert OfflineAudioContextOptions.length to an union type like (long | float) that only accept the Infinity value for float.
• When OfflineAudioContextOptions.length is Infinity and chunksSize is not provided to startRendering(), chunkSize defaults to the render quantum size. But the render quantum size is very small. Maybe, should we consider a more optimal default?
• Should OfflineAudioContextOptions.length be a multiple of chunkSize? I am assuming it doesn't need to.

(unfortunately, there is no preview available, but I think there might be something actually broken in the repo's CI pipeline)

[gabrielsanbrito]

Audio WG meeting (06/11/2026) discussion:

1. Using null is less controversial given that the length property is a long
2. The render quantum size can be configured when the OfflineAudioContext is being constructed via the renderSizeHint parameter.
3. It's not trivial to enforce since chunkSize can change with every call. At the end of the rendering, if the chunkSize is larger than the number of remaining samples, the OfflineAudioContext just returns a smaller AudioBuffer.

[mjwilson-google]

I added some comments. Also, I think I fixed the Git workflow issue if you rebase the change on the latest commit.

[mjwilson-google]

I think we should say something like the number of sample-frames to render during this call.

[mjwilson-google]

I think this should be optional unsigned long chunkSize

[mjwilson-google]

If we make length nullable I think it would become length?

[mjwilson-google]

We may want renderedFrames to be an internal slot; then we can also specify when and how it is updated.

[mjwilson-google]

It looks like the git checks are now passing but the PR preview still isn't working; sorry. I'm not sure why.