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<pre class='metadata'>
Title: WebCodecs
Repository: w3c/webcodecs
Status: ED
ED: https://w3c.github.io/webcodecs/
TR: https://www.w3.org/TR/webcodecs/
Shortname: webcodecs
Level: None
Group: mediawg
Editor: Paul Adenot, w3cid 62410, Mozilla https://www.mozilla.org/
Editor: Bernard Aboba, w3cid 65611, Microsoft Corporation https://www.microsoft.com/
Editor: Eugene Zemtsov, w3cid 139375, Google LLC https://www.google.com/
Former Editor: Chris Cunningham, w3cid 114832, Google Inc. https://www.google.com/
Abstract: This specification defines interfaces to codecs for encoding and
decoding of audio, video, and images.
This specification does not specify or require any particular codec or
method of encoding or decoding. The purpose of this specification is to
provide JavaScript interfaces to implementations of existing codec
technology developed elsewhere. Implementers are free to
support any combination of codecs or none at all.
Complain About:accidental-2119 yes
Markup Shorthands:css no, markdown yes, dfn yes
!Participate: <a href="https://github.com/w3c/webcodecs">Git Repository.</a>
!Participate: <a href="https://github.com/w3c/webcodecs/issues/new">File an issue.</a>
!Version History: <a href="https://github.com/w3c/webcodecs/commits">https://github.com/w3c/webcodecs/commits</a>
</pre>
<pre class=link-defaults>
spec:html; type:attribute; text:hidden
spec:html; type:enum-value; text:srgb
spec:infra; type:dfn; text:list
spec:infra; type:dfn; text:enqueue
</pre>
<pre class='anchors'>
spec: html; urlPrefix: https://html.spec.whatwg.org/multipage/;
for: ImageBitmap;
type: dfn; text: bitmap data; url: imagebitmap-and-animations.html#concept-imagebitmap-bitmap-data
for: ImageData
type: dfn; text: canvas pixel data; url: canvas.html#imagedata
for: Canvas;
type: dfn; text: Check the usability of the image argument; url: canvas.html#check-the-usability-of-the-image-argument
type: dfn; text: is not origin-clean; url: canvas.html#the-image-argument-is-not-origin-clean
for: webappapis;
type: dfn; text: entry settings object; url: webappapis.html#entry-settings-object
for: media;
type: dfn; text: current playback position; url: media.html#current-playback-position
type: dfn; text: live; url: infrastructure.html#live
spec: webrtc-svc; urlPrefix: https://www.w3.org/TR/webrtc-svc/
type: dfn; text: scalability mode identifier; url:#scalabilitymodes*
spec: mst-content-hint; urlPrefix: https://www.w3.org/TR/mst-content-hint/
type: dfn; text: video content hints; url:#video-content-hints
spec: ECMASCRIPT; urlPrefix: https://tc39.es/ecma262/
type: dfn; text: the current Realm; url: #current-realm
</pre>
<pre class='biblio'>
{
"H.273": {
"href": "https://www.itu.int/rec/T-REC-H.273/en",
"title": "Coding-independent code points for video signal type identification",
"publisher": "ITU",
"date": "December 2016"
},
"WEBCODECS-VIDEO-FRAME-METADATA-REGISTRY": {
"href": "https://w3c.github.io/webcodecs/video_frame_metadata_registry.html",
"title": "WebCodecs VideoFrame Metadata Registry",
"publisher": "W3C",
"authors": [
"Youenn Fablet"
],
"status": "ED"
}
}
</pre>
<style>
main > dl > dd {
margin-bottom: 1em;
}
table {
width: 100%;
}
table#sample-types td, table#sample-types th {
text-align: center;
}
table#sample-types .even {
background-color: lightgrey;
}
.rfc2119 {
text-transform: lowercase;
font-variant: small-caps;
font-style: normal;
}
</style>
Definitions {#definitions}
==========================
: <dfn>Codec</dfn>
:: Refers generically to an instance of {{AudioDecoder}}, {{AudioEncoder}},
{{VideoDecoder}}, or {{VideoEncoder}}.
: <dfn lt="Key Chunk|Key Frame">Key Chunk</dfn>
:: An encoded chunk that does not depend on any other frames for decoding. Also
commonly referred to as a "key frame".
: <dfn>Internal Pending Output</dfn>
:: Codec outputs such as {{VideoFrame}}s that currently reside in the internal
pipeline of the underlying codec implementation. The underlying codec
implementation <em class="rfc2119">MAY</em> emit new outputs only when new
inputs are provided. The underlying codec implementation <em
class="rfc2119">MUST</em> emit all outputs in response to a flush.
: <dfn lt="system resources">Codec System Resources</dfn>
:: Resources including CPU memory, GPU memory, and exclusive handles to specific
decoding/encoding hardware that <em class="rfc2119">MAY</em> be allocated by
the User Agent as part of codec configuration or generation of {{AudioData}}
and {{VideoFrame}} objects. Such resources <em class="rfc2119">MAY</em> be
quickly exhausted and <em class="rfc2119">SHOULD</em> be released immediately
when no longer in use.
: <dfn>Temporal Layer</dfn>
:: A grouping of {{EncodedVideoChunk}}s whose timestamp cadence produces a
particular framerate. See {{VideoEncoderConfig/scalabilityMode}}.
: <dfn>Progressive Image</dfn>
:: An image that supports decoding to multiple levels of detail, with lower
levels becoming available while the encoded data is not yet fully buffered.
: <dfn>Progressive Image Frame Generation</dfn>
:: A generational identifier for a given [=Progressive Image=] decoded output.
Each successive generation adds additional detail to the decoded output.
The mechanism for computing a frame's generation is implementer defined.
: <dfn>Primary Image Track</dfn>
:: An image track that is marked by the given image file as being the default
track. The mechanism for indicating a primary track is format defined.
: <dfn>RGB Format</dfn>
:: A {{VideoPixelFormat}} containing red, green, and blue color channels in
any order or layout (interleaved or planar), and irrespective of whether an
alpha channel is present.
: <dfn>sRGB Color Space</dfn>
:: A {{VideoColorSpaceInit}} containing «[
"primaries" → {{VideoColorPrimaries/bt709}},
"transfer" → {{VideoTransferCharacteristics/iec61966-2-1}},
"matrix" → {{VideoMatrixCoefficients/rgb}},
"fullRange" → `true`]».
: <dfn>REC709 Color Space</dfn>
:: A {{VideoColorSpaceInit}} containing «[
"primaries" → {{VideoColorPrimaries/bt709}},
"transfer" → {{VideoTransferCharacteristics/bt709}},
"matrix" → {{VideoMatrixCoefficients/bt709}},
"fullRange" → `false`]».
: <dfn lt="saturated">Codec Saturation</dfn>
:: The state of an underlying codec implementation where the number of active
decoding or encoding requests has reached an implementation specific
maximum such that it is temporarily unable to accept more work. The maximum
may be any value greater than 1, including infinity (no maximum). While
saturated, additional calls to `decode()` or `encode()` will be buffered
in the [=control message queue=], and will increment the respective
`decodeQueuSize` and `encodeQueueSize` attributes. The codec implementation
will become unsaturated after making sufficient progress on the current
workload.
<dfn>Codec Processing Model</dfn> {#codec-processing-model-section}
===================================================================
Background {#processing-model-background}
-----------------------------------------
<div class=non-normative>
This section is non-normative.
The codec interfaces defined by the specification are designed such that new
codec tasks can be scheduled while previous tasks are still pending. For
example, web authors can call `decode()` without waiting for a previous
`decode()` to complete. This is achieved by offloading underlying codec tasks
to a separate [=parallel queue=] for parallel execution.
This section describes threading behaviors as they are visible from the
perspective of web authors. Implementers can choose to use more threads, as
long as the externally visible behaviors of blocking and sequencing are
maintained as follows.
</div>
Control Messages {#control-messages}
------------------------------------
A <dfn>control message</dfn> defines a sequence of steps corresponding to a
method invocation on a [=codec=] instance (e.g. `encode()`).
A <dfn>control message queue</dfn> is a [=queue=] of
[=control messages=]. Each [=codec=] instance has a control message queue
stored in an internal slot named
<dfn id='control-message-queue-slot'>[[control message queue]]</dfn>.
<dfn lt="Enqueues a control message|Queue a control message">Queuing a control
message</dfn> means [=enqueuing=] the message to a [=codec=]’s [=[[control
message queue]]=]. Invoking codec methods will generally queue a control message
to schedule work.
<dfn lt="running a control message|control message steps">Running a control
message</dfn> means performing a sequence of steps specified by the method
that enqueued the message.
The steps of a given control message can block processing later messages in the
control message queue. Each [=codec=] instance has a boolean internal slot named
<dfn>[[message queue blocked]]</dfn> that is set to `true` when this occurs. A
blocking message will conclude by setting [=[[message queue blocked]]=] to
`false` and rerunning the [=Process the control message queue=] steps.
All control messages will return either `"processed"` or `"not processed"`.
Returning `"processed"` indicates the message steps are being (or have been)
executed and the message may be removed from the [=control message queue=].
`"not processed"` indicates the message must not be processed at this time
and should remain in the [=control message queue=] to be retried later.
To <dfn>Process the control message queue</dfn>, run these steps:
1. While [=[[message queue blocked]]=] is `false` and
[=[[control message queue]]=] is not empty:
1. Let |front message| be the first message in
[=[[control message queue]]=].
2. Let |outcome| be the result of running the [=control message steps=]
described by |front message|.
3. If |outcome| equals `"not processed"`, break.
4. Otherwise, dequeue |front message| from the
[=[[control message queue]]=].
Codec Work Parallel Queue {#codec-work-parallel-queue}
------------------------------------------------------
Each [=codec=] instance has an internal slot named
<dfn>[[codec work queue]]</dfn> that is a [=parallel queue=].
Each [=codec=] instance has an internal slot named
<dfn>[[codec implementation]]</dfn> that refers to the underlying platform
encoder or decoder. Except for the initial assignment, any steps that reference
[=[[codec implementation]]=] will be enqueued to the [=[[codec work queue]]=].
Each [=codec=] instance has a unique <dfn>codec task source</dfn>. Tasks
[=queue a task|queued=] from the [=[[codec work queue]]=] to the [=/event loop=]
will use the [=codec task source=].
AudioDecoder Interface {#audiodecoder-interface}
================================================
<xmp class='idl'>
[Exposed=(Window,DedicatedWorker), SecureContext]
interface AudioDecoder : EventTarget {
constructor(AudioDecoderInit init);
readonly attribute CodecState state;
readonly attribute unsigned long decodeQueueSize;
attribute EventHandler ondequeue;
undefined configure(AudioDecoderConfig config);
undefined decode(EncodedAudioChunk chunk);
Promise<undefined> flush();
undefined reset();
undefined close();
static Promise<AudioDecoderSupport> isConfigSupported(AudioDecoderConfig config);
};
dictionary AudioDecoderInit {
required AudioDataOutputCallback output;
required WebCodecsErrorCallback error;
};
callback AudioDataOutputCallback = undefined(AudioData output);
</xmp>
Internal Slots {#audiodecoder-internal-slots}
---------------------------------------------
: <dfn attribute for=AudioDecoder>[[control message queue]]</dfn>
:: A [=queue=] of [=control messages=] to be performed upon this [=codec=]
instance. See [=[[control message queue]]=].
: <dfn attribute for=AudioDecoder>[[message queue blocked]]</dfn>
:: A boolean indicating when processing the
{{AudioDecoder/[[control message queue]]}} is blocked by a pending
[=control message=]. See [=[[message queue blocked]]=].
: <dfn attribute for=AudioDecoder>[[codec implementation]]</dfn>
:: Underlying decoder implementation provided by the User Agent. See
[=[[codec implementation]]=].
: <dfn attribute for=AudioDecoder>[[codec work queue]]</dfn>
:: A [=parallel queue=] used for running parallel steps that reference the
{{AudioDecoder/[[codec implementation]]}}. See [=[[codec work queue]]=].
: <dfn attribute for=AudioDecoder>[[codec saturated]]</dfn>
:: A boolean indicating when the {{AudioDecoder/[[codec implementation]]}} is
unable to accept additional decoding work.
: <dfn attribute for=AudioDecoder>[[output callback]]</dfn>
:: Callback given at construction for decoded outputs.
: <dfn attribute for=AudioDecoder>[[error callback]]</dfn>
:: Callback given at construction for decode errors.
: <dfn attribute for=AudioDecoder>[[key chunk required]]</dfn>
:: A boolean indicating that the next chunk passed to {{AudioDecoder/decode()}}
<em class="rfc2119">MUST</em> describe a [=key chunk=] as indicated by
{{EncodedAudioChunk/[[type]]}}.
: <dfn attribute for=AudioDecoder>\[[state]]</dfn>
:: The current {{CodecState}} of this {{AudioDecoder}}.
: <dfn attribute for=AudioDecoder>\[[decodeQueueSize]]</dfn>
:: The number of pending decode requests. This number will decrease as the
underlying codec is ready to accept new input.
: <dfn attribute for=AudioDecoder>[[pending flush promises]]</dfn>
:: A list of unresolved promises returned by calls to {{AudioDecoder/flush()}}.
: <dfn attribute for=AudioDecoder>[[dequeue event scheduled]]</dfn>
:: A boolean indicating whether a {{AudioDecoder/dequeue}} event is already
scheduled to fire. Used to avoid event spam.
Constructors {#audiodecoder-constructors}
-----------------------------------------
<dfn constructor for=AudioDecoder title="AudioDecoder(init)">
AudioDecoder(init)
</dfn>
1. Let d be a new {{AudioDecoder}} object.
2. Assign a new [=queue=] to {{AudioDecoder/[[control message queue]]}}.
3. Assign `false` to {{AudioDecoder/[[message queue blocked]]}}.
4. Assign `null` to {{AudioDecoder/[[codec implementation]]}}.
5. Assign the result of starting a new [=parallel queue=] to
{{AudioDecoder/[[codec work queue]]}}.
6. Assign `false` to {{AudioDecoder/[[codec saturated]]}}.
7. Assign init.output to {{AudioDecoder/[[output callback]]}}.
8. Assign init.error to {{AudioDecoder/[[error callback]]}}.
9. Assign `true` to {{AudioDecoder/[[key chunk required]]}}.
10. Assign `"unconfigured"` to {{AudioDecoder/[[state]]}}
11. Assign `0` to {{AudioDecoder/[[decodeQueueSize]]}}.
12. Assign a new [=list=] to {{AudioDecoder/[[pending flush promises]]}}.
13. Assign `false` to {{AudioDecoder/[[dequeue event scheduled]]}}.
13. Return d.
Attributes {#audiodecoder-attributes}
-------------------------------------
: <dfn attribute for=AudioDecoder>state</dfn>
:: Returns the value of {{AudioDecoder/[[state]]}}.
: <dfn attribute for=AudioDecoder>decodeQueueSize</dfn>
:: Returns the value of {{AudioDecoder/[[decodeQueueSize]]}}.
: <dfn attribute for=AudioDecoder>ondequeue</dfn>
:: An [=event handler IDL attribute=] whose [=event handler event type=] is
{{AudioDecoder/dequeue}}.
Event Summary {#audiodecoder-event-summary}
-------------------------------------------
: <dfn event for=AudioDecoder>dequeue</dfn>
:: Fired at the {{AudioDecoder}} when the {{AudioDecoder/decodeQueueSize}} has
decreased.
Methods {#audiodecoder-methods}
-------------------------------
<dl>
<dt><dfn method for=AudioDecoder>configure(config)</dfn></dt>
<dd>
[=Enqueues a control message=] to configure the audio decoder for decoding
chunks as described by |config|.
NOTE: This method will trigger a {{NotSupportedError}} if the User Agent
does not support |config|. Authors are encouraged to first check support
by calling {{AudioDecoder/isConfigSupported()}} with |config|. User
Agents don't have to support any particular codec type or configuration.
When invoked, run these steps:
1. If |config| is not a [=valid AudioDecoderConfig=], throw a
{{TypeError}}.
2. If {{AudioDecoder/[[state]]}} is `“closed”`, throw an {{InvalidStateError}}.
3. Set {{AudioDecoder/[[state]]}} to `"configured"`.
4. Set {{AudioDecoder/[[key chunk required]]}} to `true`.
5. [=Queue a control message=] to configure the decoder with |config|.
6. [=Process the control message queue=].
[=Running a control message=] to configure the decoder means running
these steps:
1. Assign `true` to {{AudioDecoder/[[message queue blocked]]}}.
1. Enqueue the following steps to {{AudioDecoder/[[codec work queue]]}}:
1. Let |supported| be the result of running the <a>Check Configuration
Support</a> algorithm with |config|.
2. If |supported| is `false`, [=queue a task=] to run the <a>Close
AudioDecoder</a> algorithm with {{NotSupportedError}} and abort
these steps.
3. If needed, assign {{AudioDecoder/[[codec implementation]]}} with an
implementation supporting |config|.
4. Configure {{AudioDecoder/[[codec implementation]]}} with |config|.
5. [=queue a task=] to run the following steps:
1. Assign `false` to {{AudioDecoder/[[message queue blocked]]}}.
2. [=Queue a task=] to [=Process the control message queue=].
3. Return `"processed"`.
</dd>
<dt><dfn method for=AudioDecoder>decode(chunk)</dfn></dt>
<dd>
[=Enqueues a control message=] to decode the given |chunk|.
When invoked, run these steps:
1. If {{AudioDecoder/[[state]]}} is not `"configured"`, throw an
{{InvalidStateError}}.
2. If {{AudioDecoder/[[key chunk required]]}} is `true`:
1. If |chunk|.{{EncodedAudioChunk/[[type]]}} is not
{{EncodedAudioChunkType/key}}, throw a {{DataError}}.
2. Implementers <em class="rfc2119">SHOULD</em> inspect the |chunk|'s
{{EncodedAudioChunk/[[internal data]]}} to verify that
it is truly a [=key chunk=]. If a mismatch is detected, throw a
{{DataError}}.
3. Otherwise, assign `false` to
{{AudioDecoder/[[key chunk required]]}}.
3. Increment {{AudioDecoder/[[decodeQueueSize]]}}.
4. [=Queue a control message=] to decode the |chunk|.
5. [=Process the control message queue=].
[=Running a control message=] to decode the chunk means performing these
steps:
1. If {{AudioDecoder/[[codec saturated]]}} equals `true`, return `"not
processed"`.
2. If decoding chunk will cause the
{{AudioDecoder/[[codec implementation]]}} to become [=saturated=],
assign `true` to {{AudioDecoder/[[codec saturated]]}}.
3. Decrement {{AudioDecoder/[[decodeQueueSize]]}} and run the
[=AudioDecoder/Schedule Dequeue Event=] algorithm.
4. Enqueue the following steps to the {{AudioDecoder/[[codec work queue]]}}:
1. Attempt to use {{AudioDecoder/[[codec implementation]]}} to decode
the chunk.
2. If decoding results in an error, [=queue a task=] to run the
[=Close AudioDecoder=] algorithm with {{EncodingError}} and return.
3. If {{AudioDecoder/[[codec saturated]]}} equals `true` and
{{AudioDecoder/[[codec implementation]]}} is no longer
[=saturated=], [=queue a task=] to perform the following steps:
1. Assign `false` to {{AudioDecoder/[[codec saturated]]}}.
2. [=Process the control message queue=].
4. Let |decoded outputs| be a [=list=] of decoded audio data outputs
emitted by {{AudioDecoder/[[codec implementation]]}}.
5. If |decoded outputs| is not empty, [=queue a task=] to run the
[=Output AudioData=] algorithm with |decoded outputs|.
5. Return `"processed"`.
</dd>
<dt><dfn method for=AudioDecoder>flush()</dfn></dt>
<dd>
Completes all [=control messages=] in the [=control message queue=]
and emits all outputs.
When invoked, run these steps:
1. If {{AudioDecoder/[[state]]}} is not `"configured"`, return
[=a promise rejected with=] {{InvalidStateError}} {{DOMException}}.
2. Set {{AudioDecoder/[[key chunk required]]}} to `true`.
3. Let |promise| be a new Promise.
4. Append |promise| to {{AudioDecoder/[[pending flush promises]]}}.
5. [=Queue a control message=] to flush the codec with |promise|.
6. [=Process the control message queue=].
7. Return |promise|.
[=Running a control message=] to flush the codec means performing these
steps with |promise|.
1. Enqueue the following steps to the {{AudioDecoder/[[codec work queue]]}}:
1. Signal {{AudioDecoder/[[codec implementation]]}} to emit all
[=internal pending outputs=].
2. Let |decoded outputs| be a [=list=] of decoded audio data outputs
emitted by {{AudioDecoder/[[codec implementation]]}}.
3. [=Queue a task=] to perform these steps:
1. If |decoded outputs| is not empty, run the [=Output AudioData=]
algorithm with |decoded outputs|.
2. Remove |promise| from
{{AudioDecoder/[[pending flush promises]]}}.
3. Resolve |promise|.
</dd>
<dt><dfn method for=AudioDecoder>reset()</dfn></dt>
<dd>
Immediately resets all state including configuration,
[=control messages=] in the [=control message queue=], and all pending
callbacks.
When invoked, run the [=Reset AudioDecoder=] algorithm with an
{{AbortError}} {{DOMException}}.
</dd>
<dt><dfn method for=AudioDecoder>close()</df></dt>
<dd>
Immediately aborts all pending work and releases [=system resources=].
Close is final.
When invoked, run the [=Close AudioDecoder=] algorithm with an
{{AbortError}} {{DOMException}}.
</dd>
<dt><dfn method for=AudioDecoder>isConfigSupported(config)</dfn></dt>
<dd>
Returns a promise indicating whether the provided |config| is supported by
the User Agent.
NOTE: The returned {{AudioDecoderSupport}} {{AudioDecoderSupport/config}}
will contain only the dictionary members that User Agent recognized.
Unrecognized dictionary members will be ignored. Authors can detect
unrecognized dictionary members by comparing
{{AudioDecoderSupport/config}} to their provided |config|.
When invoked, run these steps:
1. If |config| is not a <a>valid AudioDecoderConfig</a>, return
[=a promise rejected with=] {{TypeError}}.
2. Let |p| be a new Promise.
3. Let |checkSupportQueue| be the result of starting a new <a>parallel
queue</a>.
4. Enqueue the following steps to |checkSupportQueue|:
1. Let |supported| be the result of running
the <a>Check Configuration Support</a> algorithm with |config|.
2. [=Queue a task=] to run the following steps:
1. Let |decoderSupport| be a newly constructed
{{AudioDecoderSupport}}, initialized as follows:
1. Set {{AudioDecoderSupport/config}} to the result of running the
<a>Clone Configuration</a> algorithm with |config|.
2. Set {{AudioDecoderSupport/supported}} to |supported|.
2. Resolve |p| with |decoderSupport|.
5. Return |p|.
</dd>
</dl>
Algorithms {#audiodecoder-algorithms}
-------------------------------------
<dl>
<dt><dfn for=AudioDecoder>Schedule Dequeue Event</dfn>
<dd>
1. If {{AudioDecoder/[[dequeue event scheduled]]}} equals `true`, return.
2. Assign `true` to {{AudioDecoder/[[dequeue event scheduled]]}}.
3. [=Queue a task=] to run the following steps:
1. Fire a simple event named {{AudioDecoder/dequeue}} at [=this=].
2. Assign `false` to {{AudioDecoder/[[dequeue event scheduled]]}}.
</dd>
<dt><dfn>Output AudioData</dfn> (with |outputs|)</dt>
<dd>
Run these steps:
1. For each |output| in |outputs|:
1. Let |data| be an {{AudioData}}, initialized as follows:
1. Assign `false` to {{platform object/[[Detached]]}}.
2. Let |resource| be the [=media resource=] described by |output|.
3. Let |resourceReference| be a reference to |resource|.
4. Assign |resourceReference| to
{{AudioData/[[resource reference]]}}.
5. Let |timestamp| be the {{EncodedAudioChunk/[[timestamp]]}} of the
{{EncodedAudioChunk}} associated with |output|.
6. Assign |timestamp| to {{AudioData/[[timestamp]]}}.
7. If |output| uses a recognized {{AudioSampleFormat}}, assign that
format to {{AudioData/[[format]]}}. Otherwise, assign `null` to
{{AudioData/[[format]]}}.
8. Assign values to {{AudioData/[[sample rate]]}},
{{AudioData/[[number of frames]]}}, and
{{AudioData/[[number of channels]]}} as determined by |output|.
3. Invoke {{AudioDecoder/[[output callback]]}} with |data|.
</dd>
<dt><dfn>Reset AudioDecoder</dfn> (with |exception|)</dt>
<dd>
Run these steps:
1. If {{AudioDecoder/[[state]]}} is `"closed"`, throw an {{InvalidStateError}}.
2. Set {{AudioDecoder/[[state]]}} to `"unconfigured"`.
3. Signal {{AudioDecoder/[[codec implementation]]}} to cease producing
output for the previous configuration.
4. Remove all [=control messages=] from the
{{AudioDecoder/[[control message queue]]}}.
5. If {{AudioDecoder/[[decodeQueueSize]]}} is greater than zero:
1. Set {{AudioDecoder/[[decodeQueueSize]]}} to zero.
2. Run the [=AudioDecoder/Schedule Dequeue Event=] algorithm.
6. For each |promise| in {{AudioDecoder/[[pending flush promises]]}}:
1. Reject |promise| with |exception|.
2. Remove |promise| from {{AudioDecoder/[[pending flush promises]]}}.
</dd>
<dt><dfn>Close AudioDecoder</dfn> (with |exception|)</dt>
<dd>
Run these steps:
1. Run the [=Reset AudioDecoder=] algorithm with |exception|.
2. Set {{AudioDecoder/[[state]]}} to `"closed"`.
3. Clear {{AudioDecoder/[[codec implementation]]}} and release associated
[=system resources=].
4. If |exception| is not an {{AbortError}} {{DOMException}},
invoke the {{AudioDecoder/[[error callback]]}} with |exception|.
</dd>
</dl>
VideoDecoder Interface {#videodecoder-interface}
================================================
<xmp class='idl'>
[Exposed=(Window,DedicatedWorker), SecureContext]
interface VideoDecoder : EventTarget {
constructor(VideoDecoderInit init);
readonly attribute CodecState state;
readonly attribute unsigned long decodeQueueSize;
attribute EventHandler ondequeue;
undefined configure(VideoDecoderConfig config);
undefined decode(EncodedVideoChunk chunk);
Promise<undefined> flush();
undefined reset();
undefined close();
static Promise<VideoDecoderSupport> isConfigSupported(VideoDecoderConfig config);
};
dictionary VideoDecoderInit {
required VideoFrameOutputCallback output;
required WebCodecsErrorCallback error;
};
callback VideoFrameOutputCallback = undefined(VideoFrame output);
</xmp>
Internal Slots {#videodecoder-internal-slots}
---------------------------------------------
: <dfn attribute for=VideoDecoder>[[control message queue]]</dfn>
:: A [=queue=] of [=control messages=] to be performed upon this [=codec=]
instance. See [=[[control message queue]]=].
: <dfn attribute for=VideoDecoder>[[message queue blocked]]</dfn>
:: A boolean indicating when processing the
{{VideoDecoder/[[control message queue]]}} is blocked by a pending
[=control message=]. See [=[[message queue blocked]]=].
: <dfn attribute for=VideoDecoder>[[codec implementation]]</dfn>
:: Underlying decoder implementation provided by the User Agent. See
[=[[codec implementation]]=].
: <dfn attribute for=VideoDecoder>[[codec work queue]]</dfn>
:: A [=parallel queue=] used for running parallel steps that reference the
{{VideoDecoder/[[codec implementation]]}}. See [=[[codec work queue]]=].
: <dfn attribute for=VideoDecoder>[[codec saturated]]</dfn>
:: A boolean indicating when the {{VideoDecoder/[[codec implementation]]}} is
unable to accept additional decoding work.
: <dfn attribute for=VideoDecoder>[[output callback]]</dfn>
:: Callback given at construction for decoded outputs.
: <dfn attribute for=VideoDecoder>[[error callback]]</dfn>
:: Callback given at construction for decode errors.
: <dfn attribute for=VideoDecoder>[[active decoder config]]</dfn>
:: The {{VideoDecoderConfig}} that is actively applied.
: <dfn attribute for=VideoDecoder>[[key chunk required]]</dfn>
:: A boolean indicating that the next chunk passed to {{VideoDecoder/decode()}}
<em class="rfc2119">MUST</em> describe a [=key chunk=] as indicated by
{{EncodedVideoChunk/type}}.
: <dfn attribute for=VideoDecoder>\[[state]]</dfn>
:: The current {{CodecState}} of this {{VideoDecoder}}.
: <dfn attribute for=VideoDecoder>\[[decodeQueueSize]]</dfn>
:: The number of pending decode requests. This number will decrease as the
underlying codec is ready to accept new input.
: <dfn attribute for=VideoDecoder>[[pending flush promises]]</dfn>
:: A list of unresolved promises returned by calls to {{VideoDecoder/flush()}}.
: <dfn attribute for=VideoDecoder>[[dequeue event scheduled]]</dfn>
:: A boolean indicating whether a {{VideoDecoder/dequeue}} event is already
scheduled to fire. Used to avoid event spam.
Constructors {#videodecoder-constructors}
-----------------------------------------
<dfn constructor for=VideoDecoder title="VideoDecoder(init)">
VideoDecoder(init)
</dfn>
1. Let d be a new {{VideoDecoder}} object.
2. Assign a new [=queue=] to {{VideoDecoder/[[control message queue]]}}.
3. Assign `false` to {{VideoDecoder/[[message queue blocked]]}}.
4. Assign `null` to {{VideoDecoder/[[codec implementation]]}}.
5. Assign the result of starting a new [=parallel queue=] to
{{VideoDecoder/[[codec work queue]]}}.
6. Assign `false` to {{VideoDecoder/[[codec saturated]]}}.
7. Assign init.output to {{VideoDecoder/[[output callback]]}}.
8. Assign init.error to {{VideoDecoder/[[error callback]]}}.
9. Assign `null` to {{VideoDecoder/[[active decoder config]]}}.
10. Assign `true` to {{VideoDecoder/[[key chunk required]]}}.
11. Assign `"unconfigured"` to {{VideoDecoder/[[state]]}}
12. Assign `0` to {{VideoDecoder/[[decodeQueueSize]]}}.
13. Assign a new [=list=] to {{VideoDecoder/[[pending flush promises]]}}.
14. Assign `false` to {{VideoDecoder/[[dequeue event scheduled]]}}.
15. Return d.
Attributes {#videodecoder-attributes}
-------------------------------------
: <dfn attribute for=VideoDecoder>state</dfn>
:: Returns the value of {{VideoDecoder/[[state]]}}.
: <dfn attribute for=VideoDecoder>decodeQueueSize</dfn>
:: Returns the value of {{VideoDecoder/[[decodeQueueSize]]}}.
: <dfn attribute for=VideoDecoder>ondequeue</dfn>
:: An [=event handler IDL attribute=] whose [=event handler event type=] is
{{VideoDecoder/dequeue}}.
Event Summary {#videodecoder-event-summary}
-------------------------------------------
: <dfn event for=VideoDecoder>dequeue</dfn>
:: Fired at the {{VideoDecoder}} when the {{VideoDecoder/decodeQueueSize}} has
decreased.
Methods {#videodecoder-methods}
-------------------------------
<dl>
<dt><dfn method for=VideoDecoder>configure(config)</dfn></dt>
<dd>
[=Enqueues a control message=] to configure the video decoder for decoding
chunks as described by |config|.
NOTE: This method will trigger a {{NotSupportedError}} if the User Agent
does not support |config|. Authors are encouraged to first check support
by calling {{VideoDecoder/isConfigSupported()}} with |config|. User Agents
don't have to support any particular codec type or configuration.
When invoked, run these steps:
1. If |config| is not a [=valid VideoDecoderConfig=], throw a
{{TypeError}}.
2. If {{VideoDecoder/[[state]]}} is `“closed”`, throw an
{{InvalidStateError}}.
3. Set {{VideoDecoder/[[state]]}} to `"configured"`.
4. Set {{VideoDecoder/[[key chunk required]]}} to `true`.
5. [=Queue a control message=] to configure the decoder with |config|.
6. [=Process the control message queue=].
[=Running a control message=] to configure the decoder means running
these steps:
1. Assign `true` to {{VideoDecoder/[[message queue blocked]]}}.
1. Enqueue the following steps to {{VideoDecoder/[[codec work queue]]}}:
1. Let |supported| be the result of running the <a>Check Configuration
Support</a> algorithm with |config|.
2. If |supported| is `false`, [=queue a task=] to run the <a>Close
VideoDecoder</a> algorithm with {{NotSupportedError}} and abort
these steps.
3. If needed, assign {{VideoDecoder/[[codec implementation]]}} with an
implementation supporting |config|.
4. Configure {{VideoDecoder/[[codec implementation]]}} with |config|.
5. [=queue a task=] to run the following steps:
1. Assign `false` to {{VideoDecoder/[[message queue blocked]]}}.
2. [=Queue a task=] to [=Process the control message queue=].
3. Return `"processed"`.
</dd>
<dt><dfn method for=VideoDecoder>decode(chunk)</dfn></dt>
<dd>
[=Enqueues a control message=] to decode the given |chunk|.
NOTE: Authors are encouraged to call {{VideoFrame/close()}} on output
{{VideoFrame}}s immediately when frames are no longer needed. The
underlying [=media resource=]s are owned by the {{VideoDecoder}} and
failing to release them (or waiting for garbage collection) can cause
decoding to stall.
NOTE: {{VideoDecoder}} requires that frames are output in the order they
expect to be presented, commonly known as presentation order. When using
some {{VideoDecoder/[[codec implementation]]}}s the User Agent will have
to reorder outputs into presentation order.
When invoked, run these steps:
1. If {{VideoDecoder/[[state]]}} is not `"configured"`, throw an
{{InvalidStateError}}.
2. If {{VideoDecoder/[[key chunk required]]}} is `true`:
1. If |chunk|.{{EncodedVideoChunk/type}} is not
{{EncodedVideoChunkType/key}}, throw a {{DataError}}.
2. Implementers <em class="rfc2119">SHOULD</em> inspect the |chunk|'s
{{EncodedVideoChunk/[[internal data]]}} to verify that
it is truly a [=key chunk=]. If a mismatch is detected, throw a
{{DataError}}.
3. Otherwise, assign `false` to
{{VideoDecoder/[[key chunk required]]}}.
3. Increment {{VideoDecoder/[[decodeQueueSize]]}}.
4. [=Queue a control message=] to decode the |chunk|.
5. [=Process the control message queue=].
[=Running a control message=] to decode the chunk means performing these steps:
1. If {{VideoDecoder/[[codec saturated]]}} equals `true`, return `"not
processed"`.
2. If decoding chunk will cause the
{{VideoDecoder/[[codec implementation]]}} to become [=saturated=],
assign `true` to {{VideoDecoder/[[codec saturated]]}}.
3. Decrement {{VideoDecoder/[[decodeQueueSize]]}} and run the
[=VideoDecoder/Schedule Dequeue Event=] algorithm.
4. Enqueue the following steps to the {{VideoDecoder/[[codec work queue]]}}:
1. Attempt to use {{VideoDecoder/[[codec implementation]]}} to decode
the chunk.
2. If decoding results in an error, [=queue a task=] to run the
[=Close VideoDecoder=] algorithm with {{EncodingError}} and return.
3. If {{VideoDecoder/[[codec saturated]]}} equals `true` and
{{VideoDecoder/[[codec implementation]]}} is no longer
[=saturated=], [=queue a task=] to perform the following steps:
1. Assign `false` to {{VideoDecoder/[[codec saturated]]}}.
2. [=Process the control message queue=].
4. Let |decoded outputs| be a [=list=] of decoded video data outputs
emitted by {{VideoDecoder/[[codec implementation]]}} in
presentation order.
5. If |decoded outputs| is not empty, [=queue a task=] to run the
[=Output VideoFrame=] algorithm with |decoded outputs|.
5. Return `"processed"`.
</dd>
<dt><dfn method for=VideoDecoder>flush()</dfn></dt>
<dd>
Completes all [=control messages=] in the [=control message queue=]
and emits all outputs.
When invoked, run these steps:
1. If {{VideoDecoder/[[state]]}} is not `"configured"`, return
[=a promise rejected with=] {{InvalidStateError}} {{DOMException}}.
2. Set {{VideoDecoder/[[key chunk required]]}} to `true`.
3. Let |promise| be a new Promise.
4. Append |promise| to {{VideoDecoder/[[pending flush promises]]}}.
5. [=Queue a control message=] to flush the codec with |promise|.
6. [=Process the control message queue=].
7. Return |promise|.
[=Running a control message=] to flush the codec means performing these
steps with |promise|.
1. Enqueue the following steps to the {{VideoDecoder/[[codec work queue]]}}:
1. Signal {{VideoDecoder/[[codec implementation]]}} to emit all
[=internal pending outputs=].
2. Let |decoded outputs| be a [=list=] of decoded video data outputs
emitted by {{VideoDecoder/[[codec implementation]]}}.
3. [=Queue a task=] to perform these steps:
1. If |decoded outputs| is not empty, run the [=Output VideoFrame=]
algorithm with |decoded outputs|.
2. Remove |promise| from
{{VideoDecoder/[[pending flush promises]]}}.
3. Resolve |promise|.
</dd>
<dt><dfn method for=VideoDecoder>reset()</dfn></dt>
<dd>
Immediately resets all state including configuration,
[=control messages=] in the [=control message queue=], and all pending
callbacks.
When invoked, run the [=Reset VideoDecoder=] algorithm with an
{{AbortError}} {{DOMException}}.
</dd>
<dt><dfn method for=VideoDecoder>close()</df></dt>
<dd>
Immediately aborts all pending work and releases [=system resources=].
Close is final.
When invoked, run the [=Close VideoDecoder=] algorithm with an
{{AbortError}} {{DOMException}}.
</dd>
<dt><dfn method for=VideoDecoder>isConfigSupported(config)</dfn></dt>
<dd>
Returns a promise indicating whether the provided |config| is supported by
the User Agent.
NOTE: The returned {{VideoDecoderSupport}} {{VideoDecoderSupport/config}}
will contain only the dictionary members that User Agent recognized.
Unrecognized dictionary members will be ignored. Authors can detect
unrecognized dictionary members by comparing
{{VideoDecoderSupport/config}} to their provided |config|.
When invoked, run these steps:
1. If |config| is not a <a>valid VideoDecoderConfig</a>, return
[=a promise rejected with=] {{TypeError}}.
2. Let |p| be a new Promise.
3. Let |checkSupportQueue| be the result of starting a new <a>parallel
queue</a>.
4. Enqueue the following steps to |checkSupportQueue|:
1. Let |supported| be the result of running
the <a>Check Configuration Support</a> algorithm with |config|.
2. [=Queue a task=] to run the following steps:
1. Let |decoderSupport| be a newly constructed
{{VideoDecoderSupport}}, initialized as follows:
1. Set {{VideoDecoderSupport/config}} to the result of running the
<a>Clone Configuration</a> algorithm with |config|.
2. Set {{VideoDecoderSupport/supported}} to |supported|.
2. Resolve |p| with |decoderSupport|.
5. Return |p|.
</dd>
</dl>
Algorithms {#videodecoder-algorithms}
-------------------------------------
<dl>
<dt><dfn for=VideoDecoder>Schedule Dequeue Event</dfn>
<dd>
1. If {{VideoDecoder/[[dequeue event scheduled]]}} equals `true`, return.
2. Assign `true` to {{VideoDecoder/[[dequeue event scheduled]]}}.
3. [=Queue a task=] to run the following steps:
1. Fire a simple event named {{VideoDecoder/dequeue}} at [=this=].
2. Assign `false` to {{VideoDecoder/[[dequeue event scheduled]]}}.
</dd>
<dt><dfn>Output VideoFrames</dfn> (with |outputs|)</dt>
<dd>
Run these steps:
1. For each |output| in |outputs|:
1. Let |timestamp| and |duration| be the
{{EncodedVideoChunk/timestamp}} and {{EncodedVideoChunk/duration}}
from the {{EncodedVideoChunk}} associated with |output|.
2. Let |displayAspectWidth| and |displayAspectHeight| be undefined.
3. If {{VideoDecoderConfig/displayAspectWidth}} and
{{VideoDecoderConfig/displayAspectHeight}} [=map/exist=] in the
{{VideoDecoder/[[active decoder config]]}}, assign their values to
|displayAspectWidth| and |displayAspectHeight| respectively.
4. Let |colorSpace| be the {{VideoColorSpace}} for |output| as detected
by the codec implementation. If no {{VideoColorSpace}} is detected,
let |colorSpace| be `undefined`.
NOTE: The codec implementation can detect a {{VideoColorSpace}} by
analyzing the bitstream. Detection is made on a best-effort
basis. The exact method of detection is implementer defined and
codec-specific. Authors can override the detected
{{VideoColorSpace}} by providing a
{{VideoDecoderConfig/colorSpace}} in the {{VideoDecoderConfig}}.
5. If {{VideoDecoderConfig/colorSpace}} [=map/exists=] in the
{{VideoDecoder/[[active decoder config]]}}, assign its value to
|colorSpace|.
6. Let |frame| be the result of running the [=Create a VideoFrame=]
algorithm with |output|, |timestamp|, |duration|,
|displayAspectWidth|, |displayAspectHeight|, and |colorSpace|.
7. Invoke {{VideoDecoder/[[output callback]]}} with |frame|.
</dd>
<dt><dfn>Reset VideoDecoder</dfn> (with |exception|)</dt>
<dd>
Run these steps:
1. If {{VideoDecoder/state}} is `"closed"`, throw an {{InvalidStateError}}.
2. Set {{VideoDecoder/state}} to `"unconfigured"`.
3. Signal {{VideoDecoder/[[codec implementation]]}} to cease producing
output for the previous configuration.
4. Remove all [=control messages=] from the
{{VideoDecoder/[[control message queue]]}}.
5. If {{VideoDecoder/[[decodeQueueSize]]}} is greater than zero:
1. Set {{VideoDecoder/[[decodeQueueSize]]}} to zero.
2. Run the [=VideoDecoder/Schedule Dequeue Event=] algorithm.
6. For each |promise| in {{VideoDecoder/[[pending flush promises]]}}:
1. Reject |promise| with |exception|.
2. Remove |promise| from {{VideoDecoder/[[pending flush promises]]}}.
</dd>
<dt><dfn>Close VideoDecoder</dfn> (with |exception|)</dt>
<dd>
Run these steps:
1. Run the [=Reset VideoDecoder=] algorithm with |exception|.
2. Set {{VideoDecoder/state}} to `"closed"`.
3. Clear {{VideoDecoder/[[codec implementation]]}} and release associated
[=system resources=].
4. If |exception| is not an {{AbortError}} {{DOMException}},
invoke the {{VideoDecoder/[[error callback]]}} with |exception|.
</dd>
</dl>
AudioEncoder Interface {#audioencoder-interface}
================================================
<xmp class='idl'>
[Exposed=(Window,DedicatedWorker), SecureContext]
interface AudioEncoder : EventTarget {
constructor(AudioEncoderInit init);
readonly attribute CodecState state;
readonly attribute unsigned long encodeQueueSize;
attribute EventHandler ondequeue;
undefined configure(AudioEncoderConfig config);
undefined encode(AudioData data);
Promise<undefined> flush();
undefined reset();
undefined close();
static Promise<AudioEncoderSupport> isConfigSupported(AudioEncoderConfig config);
};
dictionary AudioEncoderInit {
required EncodedAudioChunkOutputCallback output;
required WebCodecsErrorCallback error;
};
callback EncodedAudioChunkOutputCallback =
undefined (EncodedAudioChunk output,
optional EncodedAudioChunkMetadata metadata = {});
</xmp>
Internal Slots {#audioencoder-internal-slots}
---------------------------------------------
: <dfn attribute for=AudioEncoder>[[control message queue]]</dfn>
:: A [=queue=] of [=control messages=] to be performed upon this [=codec=]
instance. See [=[[control message queue]]=].
: <dfn attribute for=AudioEncoder>[[message queue blocked]]</dfn>
:: A boolean indicating when processing the
{{AudioEncoder/[[control message queue]]}} is blocked by a pending
[=control message=]. See [=[[message queue blocked]]=].
: <dfn attribute for=AudioEncoder>[[codec implementation]]</dfn>
:: Underlying encoder implementation provided by the User Agent. See
[=[[codec implementation]]=].
: <dfn attribute for=AudioEncoder>[[codec work queue]]</dfn>
:: A [=parallel queue=] used for running parallel steps that reference the
{{AudioEncoder/[[codec implementation]]}}. See [=[[codec work queue]]=].
: <dfn attribute for=AudioEncoder>[[codec saturated]]</dfn>
:: A boolean indicating when the {{AudioEncoder/[[codec implementation]]}} is
unable to accept additional encoding work.
: <dfn attribute for=AudioEncoder>[[output callback]]</dfn>
:: Callback given at construction for encoded outputs.
: <dfn attribute for=AudioEncoder>[[error callback]]</dfn>
:: Callback given at construction for encode errors.