OfflineAudioContext Incremental Rendering#2675
Conversation
|
@hoch @padenot @mjwilson-google, this is the first draft for While writing this, we had some open questions that might be better to discuss here:
(unfortunately, there is no preview available, but I think there might be something actually broken in the repo's CI pipeline) |
|
Audio WG meeting (06/11/2026) discussion:
|
mjwilson-google
left a comment
mjwilson-google
left a comment
There was a problem hiding this comment.
I added some comments. Also, I think I fixed the Git workflow issue if you rebase the change on the latest commit.
| @@ -2500,9 +2480,10 @@ returned promise with the rendered result as an | |||
| interface OfflineAudioContext : BaseAudioContext { | |||
| constructor(OfflineAudioContextOptions contextOptions); | |||
| constructor(unsigned long numberOfChannels, unsigned long length, float sampleRate); | |||
There was a problem hiding this comment.
If we make length nullable I think it would become length?
There was a problem hiding this comment.
Based on the discussion in the spec issue, was using length the final resolution?
There was a problem hiding this comment.
The discussion has stalled since my last comment. AFAIU, it seems that everyone agreed on using length, but there is some divergence on how it should be used. Should it be optional or nullable?
I'd rather have length be nullable instead of optional. This way callers need to be a little more intentional when creating indefinite-length OfflineAudioContexts. What do you think?
| <ol> | ||
| <li> If {{OfflineAudioContext/startRendering(chunkSize)/chunkSize}} is provided: | ||
| <ol> | ||
| <li> Let <var>renderedFrames</var> be the number of sample-frames already rendered by the {{OfflineAudioContext}}. |
There was a problem hiding this comment.
We may want renderedFrames to be an internal slot; then we can also specify when and how it is updated.
|
It looks like the git checks are now passing but the PR preview still isn't working; sorry. I'm not sure why. |
hoch
left a comment
hoch
left a comment
There was a problem hiding this comment.
Generally looks good, but I do have some suggestions. Please take a look at my comments.
Also it would be great if you can wrap the body text at column 80.
| @@ -2500,9 +2480,10 @@ returned promise with the rendered result as an | |||
| interface OfflineAudioContext : BaseAudioContext { | |||
| constructor(OfflineAudioContextOptions contextOptions); | |||
| constructor(unsigned long numberOfChannels, unsigned long length, float sampleRate); | |||
There was a problem hiding this comment.
Based on the discussion in the spec issue, was using length the final resolution?
| The total size of the audio render in sample-frames. This is the same as the | ||
| value of the <code>length</code> parameter for the constructor. | ||
|
|
||
| For undefined-length rendering, this attribute SHOULD be set to positive infinity. |
There was a problem hiding this comment.
IMO - since we have an explicit close() in this change, rendering indefinitely can be done by calling startRendering(chunkSize) repeatedly.
Probably this is aligned with what @karlt proposed?
There was a problem hiding this comment.
I am not sure if understand this comment :/ Would you mind clarifying?
When I wrote this, I intended to have length be Infinity (after the last update it should be null) because an undefined render session has no defined length.
Do you mean that we shouldn't set length to null in the undefined length scenario and this should be tracked via an internal slot? For example, we need this info when determining the size of the returned AudioBuffer. The OfflineAudioContext needs to know whether we are in an undefined-length render or not:
<li> Otherwise, if {{OfflineAudioContext/length}} is
<code>null</code>, set <var>bufferLength</var> to the
<a>render quantum size</a>.| <li> If {{OfflineAudioContext/startRendering(chunkSize)/chunkSize}} is provided: | ||
| <ol> | ||
| <li> Let <var>renderedFrames</var> be the number of sample-frames already rendered by the {{OfflineAudioContext}}. | ||
| <li> If <var>renderedFrames</var> + {{OfflineAudioContext/startRendering(chunkSize)/chunkSize}} <= {{OfflineAudioContext/length}}, set <var>bufferLength</var> to {{OfflineAudioContext/startRendering(chunkSize)/chunkSize}}. |
There was a problem hiding this comment.
nit: Let's explain this logic in descriptive prose rather than using abbreviated math.
There was a problem hiding this comment.
Thanks! Does it look good now? I was not sure if it was needed to make changes to the addition/subtraction.
3 participants
This PR proposes changes to the Web Audio spec to enable rendering audio from
OfflineAudioContextsin 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 18, 2026, 11:47 PM UTC).
More
PR Preview relies on a number of web services to run. There seems to be an issue with the following one:
🚨 Spec Generator - Spec Generator is the web service used to build bikeshed/ReSpec specs
🔗 Related URL
Error output:
[ { "lineNum": "4281:25", "messageType": "warning", "text": "At least one <img> doesn't have its size set (<img bs-line-number=\"4281:25\" alt=\"Graphical representation of calling cancelAndHoldAtTime when linearRampToValueAtTime has been called at this time.\" src=\"images/cancel-linear.svg\" style=\"height:75%;width:75%\">), but given the type of input document, Bikeshed can't figure out what the size should be.\nEither set 'width'/'height' manually, or opt out of auto-detection by setting the 'no-autosize' attribute." }, { "lineNum": "2574:9", "messageType": "fatal", "text": "Can't find the 'contextOptions' argument of method 'OfflineAudioContext/constructor(numberOfChannels, length, sampleRate)' in the argumentdef block." }, { "lineNum": "3780:9", "messageType": "fatal", "text": "Can't find the 'destinationNode' argument of method 'AudioNode/connect(destinationParam, output)' in the argumentdef block." }, { "lineNum": "3780:9", "messageType": "fatal", "text": "Can't find the 'input' argument of method 'AudioNode/connect(destinationParam, output)' in the argumentdef block." }, { "lineNum": "3881:9", "messageType": "fatal", "text": "Can't find the 'destinationNode' argument of method 'AudioNode/disconnect(destinationParam, output)' in the argumentdef block." }, { "lineNum": "3894:9", "messageType": "fatal", "text": "Can't find the 'destinationNode' argument of method 'AudioNode/disconnect(destinationParam, output)' in the argumentdef block." }, { "lineNum": "3909:9", "messageType": "fatal", "text": "Can't find the 'destinationNode' argument of method 'AudioNode/disconnect(destinationParam, output)' in the argumentdef block." }, { "lineNum": "3909:9", "messageType": "fatal", "text": "Can't find the 'input' argument of method 'AudioNode/disconnect(destinationParam, output)' in the argumentdef block." }, { "lineNum": "261:36", "messageType": "link", "text": "Multiple possible 'audio' element refs.\nArbitrarily chose https://html.spec.whatwg.org/multipage/media.html#audio\nTo auto-select one of the following refs, insert one of these lines into a <pre class=link-defaults> block:\nspec:html; type:element; text:audio\nspec:epub-34; type:element; text:audio" }, { "lineNum": "309:39", "messageType": "link", "text": "Multiple possible 'audio' element refs.\nArbitrarily chose https://html.spec.whatwg.org/multipage/media.html#audio\nTo auto-select one of the following refs, insert one of these lines into a <pre class=link-defaults> block:\nspec:html; type:element; text:audio\nspec:epub-34; type:element; text:audio" }, { "lineNum": "633:5", "messageType": "link", "text": "Multiple possible 'audio' element refs.\nArbitrarily chose https://html.spec.whatwg.org/multipage/media.html#audio\nTo auto-select one of the following refs, insert one of these lines into a <pre class=link-defaults> block:\nspec:html; type:element; text:audio\nspec:epub-34; type:element; text:audio" }, { "lineNum": "1213:9", "messageType": "link", "text": "Multiple possible 'audio' element refs.\nArbitrarily chose https://html.spec.whatwg.org/multipage/media.html#audio\nTo auto-select one of the following refs, insert one of these lines into a <pre class=link-defaults> block:\nspec:html; type:element; text:audio\nspec:epub-34; type:element; text:audio" }, { "lineNum": "2656:29", "messageType": "link", "text": "No 'idl' refs found for 'chunkSize'." }, { "lineNum": "2663:25", "messageType": "link", "text": "No 'idl' refs found for 'chunkSize'." }, { "lineNum": "2666:25", "messageType": "link", "text": "No 'idl' refs found for 'chunkSize'." }, { "lineNum": "3002:15", "messageType": "link", "text": "Multiple possible 'audio' element refs.\nArbitrarily chose https://html.spec.whatwg.org/multipage/media.html#audio\nTo auto-select one of the following refs, insert one of these lines into a <pre class=link-defaults> block:\nspec:html; type:element; text:audio\nspec:epub-34; type:element; text:audio" }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 4901:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 4901:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 5315:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 5315:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 5973:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 5973:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 5993:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 5993:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 6455:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 6455:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 7032:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 7032:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 7148:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 7148:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 7265:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 7265:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 7360:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 7360:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 7635:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 7635:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 7813:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 7813:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 8274:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 8274:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 8386:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 8386:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "8532:51", "messageType": "link", "text": "Multiple possible 'audio' element refs.\nArbitrarily chose https://html.spec.whatwg.org/multipage/media.html#audio\nTo auto-select one of the following refs, insert one of these lines into a <pre class=link-defaults> block:\nspec:html; type:element; text:audio\nspec:epub-34; type:element; text:audio" }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 8668:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 8668:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 8958:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 8958:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 9217:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 9217:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 9993:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 9993:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 10062:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 10062:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 10175:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 10175:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "23:9 of file 'audionode.include' (included by a block on 10816:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-MODE]'." }, { "lineNum": "27:9 of file 'audionode.include' (included by a block on 10816:1)", "messageType": "link", "text": "No 'idl' refs found for '[CC-INTERP]'." }, { "lineNum": "13485:1", "messageType": "warning", "text": "W3C policy requires Privacy Considerations and Security Considerations to be separate sections, but you appear to have them combined into one." }, { "lineNum": null, "messageType": "failure", "text": "Did not generate, due to errors exceeding the allowed error level." } ]This seems to be an issue with the Spec Generator service. PR Preview doesn't manage this service and so has no control over it. If you've identified an issue with it, you can report the issue to the maintainers of Spec Generator directly. Please be courteous. Thank you!
If you don't have enough information above to solve the error by yourself or if the issue doesn't seem related to Spec Generator, you can file an issue with PR Preview.