Re: Giz Explains: Why HD Video Downloads Aren't Very High Def

[David Farber <dave () farber net>]

Begin forwarded message:

From: Karl Auerbach <karl () cavebear com>
Date: October 17, 2008 6:22:39 PM EDT
To: dave () farber net
Cc: ip <ip () v2 listbox com>
Subject: Re: [IP] Giz Explains: Why HD Video Downloads Aren't Very  
High Def

David Farber wrote:

> > *From: *dewayne () warpspeed com <mailto:dewayne () warpspeed com>  
> > (Dewayne Hendricks)

> > It's all about bitrate: How much data is packed into a file...

Well, there's a bit (pun intended) more to this...

Despite what people may want to believe, packets do get lost, delayed,  
reordered, and duplicated on the net (and some bit errors in packets  
do get past the relatively weak internet checksum).

Depending on the codec and the way in which the codec is used the  
occurrence of one of these transmission errors may be simply a short- 
lived spat on the screen (or a blip in the audio) or may persist for a  
while.

There are many trade-offs, such as this resilience to impaired  
packets.  Another is how reactive the image will be to motion - will a  
high-motion scene look like on old jerky rotoscope or will motion be  
smooth?

It turns out that there is a lot that the code at the *receiving* end  
can do to deal with impaired network traffic.  For example, some dumb  
implementations simply drop out-of-order packets.  A better  
implementation would, if time constraints are met, put packets back  
into proper order and thus avoid visible or audible glitch.

It is sad how many implementations are out there that do a poor job  
when they receive anything but laboratory grade packet streams.

I tend to see more of this than most people as my company,  
InterWorking Labs, builds and sell gear that sits as a man-in-the  
middle and impairs network flows so that implementers can build more  
robust receivers.  So I may be a bit more alarmist than others.

I have heard that 802.11N will considerably increase the number of out- 
of-order packets that will be delivered.  (I don't know this for a  
fact from my own direct experience; I'm merely repeating what I've  
heard from people I trust.)  But if that is true, then we may well see  
many internet multimedia devices that work OK today not work so well  
tomorrow.

        --karl--





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