Re: [Linphone-users] Audio vs. video priority?

[Simon MORLAT]

Hello Matt,

Is the problem is an overflow when receiving, I think there's no 
solution for the receiver. The awfull audio comes that audio rtp packets 
are received too late. For video it's different, because there are less 
video packets (20/s for audio), but they are bigger, and it does not 
disturb much our eyes if an image is seen 50ms too late. For audio it's 
different, you can't catchup time, if 20ms of audio arrive too late, the 
only the receiver can do is to play 20ms of silence, hoping that's it 
going be better later.
The good solution would be that some router at your internet provider 
makes a kind of priority queue with packets it sends to you. In case it 
sees there's too much data, it sends audio rtp packets and keep video 
packets for later. This is possible to do this on linux, with 
iptable/netfilter (it's for advanced users but I'm not). However 
recognizing a video stream from an audio stream for netfilter is not 
easy. However if we arbitrary decide that the audio port will always be 
8000 and video port 9000, then it's easy.
Quality of Service is a complex problem. I'm sure it exists ietf 
protocols for telling routers to prioritize some packets, but I'm not 
sure it is implemented yet.
Anyway, changing MSSync to MSNoSync will not solve this problem.
Regards,
Simon

Matt Lawson wrote:

> I am using Linphone with Asterisk and it works pretty well, 
> particularly when bandwidth is plentiful.  However, we are also trying 
> to connect some machines which are using residential DSL lines 
> (maximum 256kbps upstream) and we always eventually run out of 
> bandwidth (remember they may have other things happening than just 
> Linphone).
>
> What I notice is that the video stays together pretty well, but the 
> audio breaks up horribly when bandwidth starts to run out.
>
> My question is, is there any way to give the audio stream "priority" 
> over the video?  With a video call, the image is a 'bonus' but the 
> users will expect the audio to be perfect, or at least understandable.
>
> The way our Linphone is now (it is not exactly like the CVS version, 
> because it is a few months old), it uses the normal audio timer sync 
> (20ms or whatever it is) and uses "no sync" for the video.  We 
> discovered that this gave the best image quality.  But I wonder, is 
> that causing the audio to be lost in favor of video?  Should I put the 
> video on a timer also?  Or should I change the audio to "no sync" as 
> well?  Is there any other way to tweak it so that audio will be sure 
> to come through at the expense of the video?
>
> Suggestions welcome.  Thanks.
>
> - Matt
>
>
>
>
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