[streaming] Re: Reliable streaming format for wireless links

[Niall Donegan]

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Marshall Eubanks wrote:
> 
> On Mar 13, 2006, at 12:18 PM, Thomas Kernen wrote:
> 
>>> The other thing is the size of your GOP. Can you shorten it ? 
>>> Suppose you are sending out 100 pps
>>> (packets per second) and the GOP is 30 seconds. Then, 1 packet  lost
>>> out of 3000 will mess things up,
>>> on average for 15 seconds. If you can lower the GOP to 30 frames  (1
>>> second), then the same packet loss rate
>>> will case errors for 1 second out of 30, lasting on average for  0.5
>>> seconds, which is a lot
>>> more tolerable.
>>> I always try and lower the GOP for streaming.
>>
>>
>> Shorter GOP would therefore mean a higher bitrate due to the 
>> increased number of I-frames. So that may cause more issues with  APs
>> that can't handle multicast properly?!?
>>
> 
> Yes, if the quality is kept constant. (Well, sort off. This is true  if
> your packet losses are caused by thermal noise. In many cases,  however,
> packet losses are caused by other events, and are thus not  random. If
> the WLAN is overloaded for 1 second, then for a 30 second  GOP you are
> killed by
> on average 15 seconds, regardless of the bit rate.)
> 
> In any case, in the streaming projects I have worked with, the bit
> rate is more or less constant (or at least has an upper bound), which 
> is set by cost of bandwidth or
> availability of bandwidth.
> 
> In that case a shorter GOP means (in some average sense) lower  quality
> if the bit rate is kept constant. That's how I generally  think of it,
> and I was assuming that the bit rate is constant or at  least capped.

Pardon my ignorance, but what exactly is GOP? From the description of
how it would affect the performance, I'm thinking that it's related to
the Beacon setting on the Linksys APs. Would I be anywhere close to the
mark?

- --
Niall Donegan
niall\at\moybella\dot\net
Public-Key: http://moybella.net/~niall/public.gpg
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