[Asterisk-video] Re: [asterisk-dev] Video packetization proposal

Mihai Balea mihai at hates.ms
Mon Jun 4 07:48:06 MST 2007

On Jun 3, 2007, at 1:08 PM, Sergio Garcia Murillo wrote:
> h263-1998/2000 behaves exactly the same way and it has make my
> life much more easier than h263-1996.
> Also, if you miss one packet (I've never seen an missordered one) or
> you add data redundancy to the stream or your next frames will
> be displayed incorrectly.

That is correct.  However, dropping one p-frame will result in less  
crappiness than using an incomplete or screwed-up one.
I thought about adding redundancy using some sort of FEC, but the  
reality is that dropped packets usually happen when there is some  
sort of network congestion, and pushing even more data on the pipe  
does not help in that situation.  I have not done any real testing in  
this area, so I'm not speaking from experience here.  If you, or  
anybody else for that matter, have played with video data redundancy,  
I'd be very interested in hearing about your results.

>> Compare to H.264 which does have built in packetization and is
>> resistant to lost or miss-ordered packets.
> Video packetizating is thigthly coupled with the encoding and the  
> decoding
> process. If your going to offer good error correction capabilities  
> you'll
> have
> to implement it directly into de encoder/decoder (have you ever  
> tried to
> packetize h263-1996?) and don't mix it with the transport.

I agree that this should be handled at the codec level.  However,  
Theora doesn't do it so we have to work with what we have.   
Unfortunately, I am not a DSP expert, so I cannot really dig into  
Theora's internals to add these features myself.


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