Re: [payload] VP8 payload, decoder processing capabilities

[Olivier Crête <[e-mail]>]

On Tue, 2012-04-24 at 21:31 +0000, Sandy (Alexander) MacInnis wrote:
> I have another question about this.
> 
> Background:
> In the VP8 bitstream spec, and in the payload draft, the use of multiple coefficient partitions is optional and not required. 
> 
> A VP8 decoder might use multi-threaded processing, such that it can achieve significantly greater throughput by decoding multiple coefficient partitions in parallel. Such a decoder might rely on the presence of a certain number of coefficient partitions in order to achieve a certain level of throughput.
> 
> For example, some receiver might comprise a multi-threaded decoder that can decode 1920x1080p60 if the stream has at least four coefficient partitions, but if the stream has only one coefficient partition it might be limited to a significantly smaller product of frame size and frame rate.
> 
> Question: With the current draft, how does a multi-threaded decoder know in advance how many coefficient partitions the stream uses, so it can decide whether it can decode a stream of a given frame size and frame rate? Or does this aspect not matter?

I think the receiver should include all of that in its SDP, maybe
something like: SamplesPerCoefficientPartition=X
MaxParallelCoeffficientPartitions=Y

That said, I'm concerned that all of this is a really static view of
things, which is useful on a fixed device. But is completely pointless
when writing software that runs on a general purpose computer (such as a
desktop or a smartphone), in which case we want something more dynamic.
So maybe all of this discussion is mostly pointless and we should push
for a more dynamic solution (maybe some kind of RTCP feedback?)

-- 
Olivier Crête
[e-mail]