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which needs to be added to the remote codecs a=fmtp: This also forces SimulcastCastEncoderAdapter to avoid issues with codecs that have native simulcast capability but do require synchronized keyframes. This parameter allows for large-scale experimentation and A/B testing whether the new behavior has advantages. It is to be considered transitional and may be removed again in the future. BUG=webrtc:10107 Change-Id: I81f496c987b2fed7ff3089efb746e7e89e89c033 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/333560 Reviewed-by: Harald Alvestrand <hta@webrtc.org> Commit-Queue: Philipp Hancke <phancke@microsoft.com> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org> Cr-Commit-Position: refs/heads/main@{#41805}
37 lines
1.5 KiB
Markdown
37 lines
1.5 KiB
Markdown
# x-google-per-layer-pli FMTP parameter
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The x-google-per-layer-pli FMTP parameter is a format specific parameter
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that can be added to a remote description in the `a=fmtp:` line:
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a=fmtp:96 x-google-per-layer-pli=1
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When using simulcast with more than a single SSRC, it will change how the
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simulcast encoder reacts to Picture Loss Indication (PLI) and Full Intra
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Request (FIR) RTCP feedback.
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When the parameter value is 1, a PLI requests the generation of a key frame
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for the spatial layer associated with the SSRC of the media source and a
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FIR does the same for the SSRC value of the media sender.
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When the value is 0 or the parameter is missing, a keyframe is generated
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on all spatial layers for backward compability.
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## Experimentation
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This parameter does allow for large-scale A/B testing and opt-in to the
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new behavior. For multiparty calls enabling it should reduce the number of
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keyframes sent by the client and number of key frames received by the
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receivers which results in a better bandwidth utilization.
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This parameter is experimental and may be removed again in the future.
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## IANA considerations
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Since the current behavior of reacting to a PLI for a specific SSRC with
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key frames on all spatial layers can be considered an implementation bug
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this parameter is not registered with the IANA.
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If experimentation shows that the current behavior is better for some
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codecs like VP8 which can share encoding parameters with synchronous
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keyframes a standardized variant of this parameter shall be registered
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with the IANA.
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