Subject: [AVT] Audio/Video and packet loss

From: "Alejandro Cabrera Obed" <[email-masked]>
Date: Fri, 21 Apr 2006 14:42:10 -0300

Hi people, I have a brief question....

In general, which type of media flow (audio or video) is more affected with
packet loss in an IP network ???

Is this just dependant on the CODEC algorithm used by the audio or video or
maybe there is a media that is more sensitive for any given reason ???

Thanks a lot.

Alejandro

--
Alejandro Cabrera Obed
[email-masked]
_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

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From: Dave Singer <[email-masked]>
Date: Fri, 21 Apr 2006 11:33:46 -0700

At 14:42  -0300 21/04/06, Alejandro Cabrera Obed wrote:
>In general, which type of media flow (audio or video) is more 
>affected with packet loss in an IP network ???
>
>Is this just dependant on the CODEC algorithm used by the audio or 
>video or maybe there is a media that is more sensitive for any given 
>reason ???

In general, video tends to be more affected than audio.  The reason 
is that audio tends to encode each time-interval independently, or 
almost so (AAC, for example, needs two consecutive frames for the 
second to be *perfectly* decoded), whereas in video, extensive 
frame-differencing is usually done ('motion estimation' and so on). 
That means that an error affects not only the frame for which data 
was lost, but also any frame which predicts from the incorrect 
portion of that frame.  This causes 'ghosting' and other artifacts 
that can persist for some time (until those regions are painted again 
with correct data).  The affect can be mitigated but not eliminated 
by estimating what was lost, and so on.

Hope this helps
-- 
David Singer
Apple Computer/QuickTime

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From: Ladan Gharai <[email-masked]>
Date: Fri, 21 Apr 2006 14:54:29 -0400

On Apr 21, 2006, at 2:33 PM, Dave Singer wrote:

>> video or maybe there is a media that is more sensitive for any  
>> given reason ???
>>
>
> frame-differencing is usually done

    but if the video was also compressed frame by frame only (i.e.M- 
JPEG), or better yet not compressed at all, doesn't a dropped audio  
packet  impair a users perception of media quality, more than a  
dropped video packet?
   mostly because we are less tolerant of audio glitches, and more  
forgiving with video

> ('motion estimation' and so on). That means that an error affects  
> not only the frame for which data was lost, but also any frame  
> which predicts from the incorrect portion of that frame.  This  
> causes 'ghosting' and other artifacts that can persist for some  
> time (until those regions are painted again with correct data).   
> The affect can be mitigated but not eliminated by estimating what  
> was lost, and so on.
>
> Hope this helps
> -- 
> David Singer
> Apple Computer/QuickTime
>