Re: [AVT] AVT opinions required on Vorbis over RTP

On 2 Sep 2005, at 19:50, Tor-Einar Jarnbjo wrote:
>> In H.264, we have data structures known as parameter sets, which  
>> are very
>> sensitive to errors and which need to be available before the  
>> decoding of
>> the actual slice data starts.  I guess that makes them comparable  
>> to a
>> vorbis codebook.  Likely they are smaller; perhaps much smaller,  
>> though.  I
>> don't know vorbis enough to make a judgment here.  A typical  
>> parameter set
>> is only a couple of bytes, but it can grow to several hundred  
>> bytes per set,and we need more than one (perhaps many) of them.
>>
>>
> Perhaps I should have explained the details a bit more thrououghly.  
> The Vorbis codebook size depends on the encoder and have (in  
> theory) no size limitation. The reference encoder creates codebooks  
> at around 5kB for common bit rates. I think SDPs are recommended to  
> be kept below 1kB, so including the codebook header in the SDP is  
> not an option and I am concerned that repeating the codebooks at  
> the session beginning will result in unacceptable delays before  
> audio transmission can start. We must also try to find a solution  
> which will work in multicast situations.

The 1kB recommendation is for SDP carried in SAP, since it has to fit  
within a single UDP packet. If the SDP is delivered by other means,  
e.g. SIP, RTSP, web page, then there is no size limit (although,  
clearly, smaller is better if you want to reduce setup delays).

Colin

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