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Oct 26, 2023
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Add <em> tags for RFC2119 key words #730

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93 changes: 50 additions & 43 deletions index.src.html
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Original file line number Diff line number Diff line change
Expand Up @@ -2028,9 +2028,9 @@

<dt><dfn dict-member for=VideoDecoderConfig>optimizeForLatency</dfn></dt>
<dd>
Hint that the selected decoder SHOULD be configured to minimize the number
of {{EncodedVideoChunk}}s that have to be decoded before a {{VideoFrame}}
is output.
Hint that the selected decoder <em class="rfc2119">SHOULD</em> be configured
to minimize the number of {{EncodedVideoChunk}}s that have to be decoded
before a {{VideoFrame}} is output.

NOTE: In addition to User Agent and hardware limitations, some codec
bitstreams require a minimum number of inputs before any output can be
Expand Down Expand Up @@ -2236,16 +2236,17 @@

When supported, hardware acceleration offloads encoding or decoding to
specialized hardware. {{HardwareAcceleration/prefer-hardware}} and
{{HardwareAcceleration/prefer-software}} are hints. While User Agents SHOULD
respect these values when possible, User Agents may ignore these values in some
or all circumstances for any reason.
{{HardwareAcceleration/prefer-software}} are hints. While User Agents
<em class="rfc2119">SHOULD</em> respect these values when possible, User
Agents may ignore these values in some or all circumstances for any reason.

To prevent fingerprinting, if a User Agent implements [[media-capabilities]],
the User Agent MUST ensure rejection or acceptance of a given
{{HardwareAcceleration}} preference reveals no additional information on top of
what is inherent to the User Agent and revealed by [[media-capabilities]]. If a
User Agent does not implement [[media-capabilities]] for reasons of
fingerprinting, they SHOULD ignore the {{HardwareAcceleration}} preference.
the User Agent <em class="rfc2119">MUST</em> ensure rejection or acceptance of
a given {{HardwareAcceleration}} preference reveals no additional information
on top of what is inherent to the User Agent and revealed by
[[media-capabilities]]. If a User Agent does not implement
[[media-capabilities]] for reasons of fingerprinting, they
<em class="rfc2119">SHOULD</em> ignore the {{HardwareAcceleration}} preference.

<div class='note'>
NOTE: Good examples of when a User Agent can ignore
Expand Down Expand Up @@ -2395,9 +2396,10 @@
<dl>
<dt><dfn dict-member for=VideoEncoderEncodeOptions>keyFrame</dfn></dt>
<dd>
A value of `true` indicates that the given frame MUST be encoded as a key
frame. A value of `false` indicates that the User Agent has flexibility to
decide whether the frame will be encoded as a [=key frame=].
A value of `true` indicates that the given frame
<em class="rfc2119">MUST</em> be encoded as a key frame. A value of `false`
indicates that the User Agent has flexibility to decide whether the frame
will be encoded as a [=key frame=].
</dd>
</dl>

Expand Down Expand Up @@ -3245,24 +3247,26 @@
but audio content using 24-bit samples is common, so 32-bits integers are
commonly used to hold 24-bit content.

{{AudioData}} containing 24-bit samples SHOULD store those samples in {{s32}} or
{{f32}}. When samples are stored in {{s32}}, each sample MUST be left-shifted by
`8` bits. By virtue of this process, samples outside of the valid 24-bit range
([-8388608, +8388607]) will be clipped. To avoid clipping and ensure lossless
transport, samples <em class="rfc2119">MAY</em> be converted to {{f32}}.
{{AudioData}} containing 24-bit samples <em class="rfc2119">SHOULD</em> store those
samples in {{s32}} or {{f32}}. When samples are stored in {{s32}}, each sample
<em class="rfc2119">MUST</em> be left-shifted by `8` bits. By virtue of this
process, samples outside of the valid 24-bit range ([-8388608, +8388607]) will
be clipped. To avoid clipping and ensure lossless transport, samples
<em class="rfc2119">MAY</em> be converted to {{f32}}.

NOTE: While clipping is unavoidable in {{u8}}, {{s16}}, and {{s32}} samples due
to their storage types, implementations SHOULD take care not to clip internally
when handling {{f32}} samples.
to their storage types, implementations <em class="rfc2119">SHOULD</em> take
care not to clip internally when handling {{f32}} samples.

### Audio channel ordering ### {#audio-channel-ordering}

When decoding, the ordering of the audio channels in the resulting {{AudioData}}
MUST be the same as what is present in the {{EncodedAudioChunk}}.
<em class="rfc2119">MUST</em> be the same as what is present in the
{{EncodedAudioChunk}}.

When encoding, the ordering of the audio channels in the resulting
{{EncodedAudioChunk}} MUST be the same as what is preset in the given
{{AudioData}};
{{EncodedAudioChunk}} <em class="rfc2119">MUST</em> be the same as what is
preset in the given {{AudioData}}.

In other terms, no channel reordering is performed when encoding and decoding.

Expand Down Expand Up @@ -3820,8 +3824,8 @@
:: 1. If |overrideColorSpace| is provided, return a new {{VideoColorSpace}}
constructed with |overrideColorSpace|.

User Agents MAY replace `null` members of the provided
|overrideColorSpace| with guessed values as determined by implementer
User Agents <em class="rfc2119">MAY</em> replace `null` members of the
provided |overrideColorSpace| with guessed values as determined by implementer
defined heuristics.

2. Otherwise, if {{VideoFrame/[[format]]}} is an [=RGB format=] return a new
Expand Down Expand Up @@ -4333,7 +4337,8 @@
integer. Samples are arranged starting at the top left of the image.

The visible rectangle offset ({{VideoFrame/visibleRect}}.{{DOMRectInit/x}}
and {{VideoFrame/visibleRect}}.{{DOMRectInit/y}}) MUST be even.
and {{VideoFrame/visibleRect}}.{{DOMRectInit/y}})
<em class="rfc2119">MUST</em> be even.
</dd>
<dt><dfn enum-value for=VideoPixelFormat>I420A</dfn></dt>
<dd>
Expand All @@ -4360,7 +4365,8 @@
integer. Samples are arranged starting at the top left of the image.

The visible rectangle offset ({{VideoFrame/visibleRect}}.{{DOMRectInit/x}}
and {{VideoFrame/visibleRect}}.{{DOMRectInit/y}}) MUST be even.
and {{VideoFrame/visibleRect}}.{{DOMRectInit/y}})
<em class="rfc2119">MUST</em> be even.

{{I420A}}'s [=equivalent opaque format=] is {{I420}}.
</dd>
Expand All @@ -4387,7 +4393,7 @@
are arranged starting at the top left of the image.

The visible rectangle offset ({{VideoFrame/visibleRect}}.{{DOMRectInit/x}})
MUST be even.
<em class="rfc2119">MUST</em> be even.
</dd>
<dt><dfn enum-value for=VideoPixelFormat>I444</dfn></dt>
<dd>
Expand Down Expand Up @@ -4430,7 +4436,8 @@
at the top left of the image.

The visible rectangle offset ({{VideoFrame/visibleRect}}.{{DOMRectInit/x}}
and {{VideoFrame/visibleRect}}.{{DOMRectInit/y}}) MUST be even.
and {{VideoFrame/visibleRect}}.{{DOMRectInit/y}})
<em class="rfc2119">MUST</em> be even.

<div class=example>
An image in the NV12 pixel format that is 16 pixels wide and 10 pixels tall
Expand Down Expand Up @@ -5575,14 +5582,14 @@
Resource Reclamation{#resource-reclamation}
==============================================

When resources are constrained, a User Agent MAY proactively reclaim codecs.
This is particularly true in the case where hardware codecs are limited, and
shared accross web pages or platform apps.
When resources are constrained, a User Agent <em class="rfc2119">MAY</em>
proactively reclaim codecs. This is particularly true in the case where hardware
codecs are limited, and shared accross web pages or platform apps.

To <dfn>reclaim a codec</dfn>, a User Agent MUST run the appropriate
close algorithm (amongst [=Close AudioDecoder=], [=Close AudioEncoder=],
[=Close VideoDecoder=] and [=Close VideoEncoder=]) with a {{QuotaExceededError}}
{{DOMException}}.
To <dfn>reclaim a codec</dfn>, a User Agent <em class="rfc2119">MUST</em> run
the appropriate close algorithm (amongst [=Close AudioDecoder=],
[=Close AudioEncoder=], [=Close VideoDecoder=] and [=Close VideoEncoder=]) with
a {{QuotaExceededError}} {{DOMException}}.

The rules governing when a codec may be reclaimed depend on whether the codec is
an [=active=] or [=inactive=] codec and/or a [=background=] codec.
Expand All @@ -5604,13 +5611,13 @@
{{ownerDocument}} (or [=owner set=]'s {{Document}}, for codecs in workers) has a
{{Document/hidden}} attribute equal to `true`.

A User Agent MUST only [=reclaim a codec=] that is either an
[=inactive codec=], a [=background codec=], or both. A User Agent MUST NOT
reclaim a codec that is both [=active=] and in the foreground, i.e. not a
[=background codec=].
A User Agent <em class="rfc2119">MUST</em> only [=reclaim a codec=] that is
either an [=inactive codec=], a [=background codec=], or both. A User Agent
<em class="rfc2119">MUST NOT</em> reclaim a codec that is both [=active=] and in
the foreground, i.e. not a [=background codec=].

Additionally, User Agents MUST NOT reclaim an [=active=] [=background=] codec
if it is:
Additionally, User Agents <em class="rfc2119">MUST NOT</em> reclaim an [=active=]
[=background=] codec if it is:
- An encoder, e.g. an {{AudioEncoder}} or {{VideoEncoder}}.

NOTE: This prevents long running encode tasks from being interrupted.
Expand Down