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Re: WebRTC NV Use Cases

From: Mészáros Mihály <misi@niif.hu>
Date: Tue, 19 Jun 2018 09:47:35 +0200
To: public-webrtc@w3.org
Message-ID: <362d7547-88c2-6b61-f5de-93c31a7076ad@niif.hu>
Let me add few additional comment from Claudio inline.

He has much more understanding according his experiences with the
mentioned tool LOLA.

2018-06-18 18:23 keltezéssel, Harald Alvestrand írta:
> On 06/18/2018 05:21 PM, Mészáros Mihály wrote:
>>
>> You are right it is low latency audio and video.
>>
>> The key how low it could be. Ultra low latency is important for
>> performing arts.
>>
>> Requirements what I could think about is to turning off the jitter
>> buffer totally, raw audio codec, (may skip encryption), no packet
>> checksum counting, so to avoid anything that could add any latency.
>>
>
> The requirement for reasonable quality in conversation is ~100 ms
> microphone-to-ear.
>
> The requirement for musicians playing together is (depending on who
> you ask) between 5 and 20 ms microphone-to-ear.
>

> * What are the latency requirements?

for simultaneous real time playing together, the sustainable RTT time
(note! RTT!) is below 50ms maximum, with the confort range below 35ms
for any kind of music, includint real time-synch demanding one. For some
kind of music where time is more relaxed you can add about 10ms to the RTT.

If you do a masterclass, where real time playing together is less
demanding the RTT time can exceed 100ms so also intercontinental
masterclasses can work with low latency systems. You can still work up
to 350 / 400 ms RTT but then all sort of audio echo control issues
arise, and you are again in troubles because controlling the echo oten
means affecting the sound quality.

 > * What other optimization we need to consider?

namely jitter: a high jitter make the A/V streaming slow because then
you need to add buffering, and buffering increases the latency
significanty: each 1K data packet buffers with the lowest audio sampling
size (32 or 64) increases the latency of abobut 1ms; in clean low jitter
networks you can run with 1 buffer... but if jitter is significant, you
need at least 7 - 10 buffers, which puts you quickly out of the comfort
zone.

You also need to reduce in general buffering in all libraries involved,
and also the I/O path from the NIC to the CPU/Memory shall be quick and
smooth. Interrupts to the kernel/CPU also matter a lot.r

> * Any hints other hint would be appreciated.

in general, minimizing processing time, and buffering is a matter of
parallel processing, so applications should try to use at best the
multi-core architecture which modern CPUs offer.


Misi
>>
>> Misi
>>
>>
>> 2018-06-18 17:05 keltezéssel, Peter Thatcher írta:
>>> How is it different than an audio call, which allows attempts to be
>>> as low-latency as possible?  Is there a requirement for this use
>>> case that we don't already have?
>>>
>>> On Mon, Jun 18, 2018 at 11:43 AM Mészáros Mihály <bakfitty@gmail.com
>>> <mailto:bakfitty@gmail.com>> wrote:
>>>
>>>     2018-05-09 21:29 keltezéssel, Bernard Aboba írta:
>>>>     On June 19-20 the WebRTC WG will be holding a face-to-face meeting in Stockholm, which will focus largely on WebRTC NV. 
>>>>
>>>>     Early on in the discussion, we would like to have a discussion of the use cases that WebRTC NV will address. 
>>>>
>>>>     Since the IETF has already published RFC 7478, we are largely interested in use cases that are either beyond those articulated in RFC 7478, or use cases in the document that somehow can be done better with WebRTC NV than they could with WebRTC 1.0. 
>>>>
>>>>     As with any successful effort, we are looking for volunteers to develop a presentation for the F2F, and perhaps even a document. 
>>>>
>>>     Hi,
>>>
>>>     Let me add one possible WebRTC Use Case: Ultra Low Latency
>>>     audio/ video for musical performances and other performing arts
>>>     with WebRTC
>>>     Tuned WebRTC stack for ultra low latency.
>>>
>>>     SW/HW solution that we use actually to solve the use case
>>>     e.g.
>>>
>>>       * http://www.ultragrid.cz/
>>>       * https://www.garr.it/en/communities/music-and-art/lola
>>>
>>>     Read more on tools and use case on https://npapws.org/ :
>>>
>>>       * https://npapws.org/wp-content/uploads/2017/01/S.Ubik-J.Melnikov-Network-delay-management-2017.pptx
>>>       * https://npapws.org/wp-content/uploads/2016/02/Performing-Arts-and-Advanced-Networking.pptx
>>>
>>>     Regards,
>>>     Misi
>>>
>>
>
> -- 
> Surveillance is pervasive. Go Dark.
Received on Tuesday, 19 June 2018 07:48:32 UTC

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