LGTM2
On 8/22/23 10:10 AM, Yoav Weiss wrote:
LGTM1. Mirroring video codecs makes sense. Glad to see Mozilla being
supportive.
On Thu, Aug 17, 2023 at 8:51 PM 'Thomas Guilbert' via blink-dev
<blink-dev@chromium.org> wrote:
Contact emails
tguilb...@google.com
Explainer
None
Specification
https://w3c.github.io/webcodecs/#dom-audioencoderconfig-bitratemode
<https://w3c.github.io/webcodecs/#dom-audioencoderconfig-bitratemode>
Summary
Some audio codecs support specifying the audio encoder bitrate
modes. This feature adds a "bitrateMode" flag with a default value
of “variable” to WebCodec's AudioEncoderConfig, which mirrors the
functionality already present for VideoEncoderConfig
<https://w3c.github.io/webcodecs/#dom-videoencoderconfig-bitratemode>.
This flag will allow web authors to choose between encoding audio
with a variable bitrate or a constant bitrate. Specific codec
encoder implementations might have slightly different terminology
(e.g. `CBR` vs `VBR` for Opus), but all of them should map to the
general concept of "constant" versus "variable" bitrate.
The two options have the following effects:
*
“variable”: allows an audio encoder to increase or lower its
bitrate according to the content of the audio it is encoding,
in order to preserve bandwidth/binary-size, while still
maintaining a target quality. For example, an encoder might
lower its bitrate when encoding silence, and revert to a full
bitrate when encoding speech.
*
“constant” : forces an audio encoder to maintain the same
bitrate, regardless of the audio content. This can be useful
when a predictable bandwidth consumption is preferable.
As of M118, this flag will affect two codecs on Chromium: Opus and
AAC.
Blink component
Blink>Media>WebCodecs
<https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink%3EMedia%3EWebCodecs>
TAG review
None
TAG review status
Not applicable
Risks
Interoperability and Compatibility
The risk is low. Firefox has not yet shipped WebCodecs, but is
currently developing it. Safari has developed video WebCodecs, but
not yet audio. The flag should be easy for other browsers to add
as they implement WebCodecs.
Gecko: Positive
(https://github.com/mozilla/standards-positions/issues/837
<https://github.com/mozilla/standards-positions/issues/837>)
WebKit: No signal
(https://github.com/WebKit/standards-positions/issues/218
<https://github.com/WebKit/standards-positions/issues/218>)
Web developers: Positive, as feature was originally a developper
request – https://github.com/w3c/webcodecs/issues/649
<https://github.com/w3c/webcodecs/issues/649>
Other signals:
WebView application risks
This change does not deprecate existing APIs, and only supplements
existing APIs, with a sensible default. This should not be a
WebView risk.
Debuggability
Will this feature be supported on all six Blink platforms
(Windows, Mac, Linux, Chrome OS, Android, and Android
WebView)?
Yes
Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?
It will be at the time it is implemented. Example test
<https://chromium-review.googlesource.com/c/chromium/src/+/4654994/1/third_party/blink/web_tests/external/wpt/webcodecs/audio-encoder-codec-specific.https.any.js>.
Flag name on chrome://flags
N/A
Finch feature name
N/A
Non-finch justification
Simple parameter change
Requires code in //chrome?
False
Tracking bug
https://bugs.chromium.org/p/chromium/issues/detail?id=1462467
<https://bugs.chromium.org/p/chromium/issues/detail?id=1462467>
Estimated milestones
Shipping on desktop
118
Shipping on Android
118
Anticipated spec changes
None
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5084320053592064
<https://chromestatus.com/feature/5084320053592064>
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