Re: [AVTCORE] Proposed addition to VP9 RTP payload: advance signaling of inter-layer dependency

Alexandre GOUAILLARD <> Wed, 10 June 2020 11:10 UTC

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From: Alexandre GOUAILLARD <>
Date: Wed, 10 Jun 2020 13:10:29 +0200
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To: Jonathan Lennox <>
Cc:, Sergey Silkin <>
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Subject: Re: [AVTCORE] Proposed addition to VP9 RTP payload: advance signaling of inter-layer dependency
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+1 support.

On Tue, Jun 9, 2020 at 11:27 PM Jonathan Lennox <>

> Hi, all —
> Sergey Silkin of Google has proposed an addition to the VP9 RTP payload.
> The problem he’s observed is that when a lower spatial layer frame of a
> picture is not used for prediction by a higher layer, in the current spec
> it’s only possible to know this when the higher-layer frame is received
> (based on its “D” bit).  This means that if a middlebox or decoder would
> need to buffer the packets of the lower-layer frame in order to decide
> reliably whether or not it needs to be relayed or decoded.
> Sergey’s proposal (with some wording tweaks by me) is to use the
> currently-reserved bit in the first byte of the VP9 payload header as a “Z”
> byte, defined as:
>           Z: Not a reference frame for upper spatial
>           layers. If set to 1, indicates that frames with higher
>           spatial layers SID+1 of the current and following pictures
>           do not depend on the current spatial layer SID frame.  This
>           enables a decoder which is targeting a higher spatial layer
>           to know that it can safely discard this packet's frame
>           without processing it, without having to wait for the "D"
>           bit in the higher-layer frame (see below).
> This has been implemented (and is being used) in Chrome, which is by far
> the dominant VP9 RTP payload implementation.
> As this solves a real problem and is being used in running code, my
> inclination is to add it to the spec. Are there any objections?
> The pull request to add this to the spec is at
> .
> Jonathan Lennox
> (Writing as document editor)
> _______________________________________________
> Audio/Video Transport Core Maintenance

Alex. Gouaillard, PhD, PhD, MBA
President - CoSMo Software Consulting, Singapore