[h323plus] H.261 and G.722

Alessandro Angeli packetizer.com at riseoftheants.com
Mon Jan 10 15:50:24 EST 2011

From: "Jan Willamowius" <jan at willamowius.de>
Date: Monday 10 January 2011 04:30

> after your change to the H.261 plugin, it stopped working for me: With
> the new plugin, I only receive a black video stream with Spranto and
> Polycom PVX.
> I had tested the old plugin with Polycom PVX, Polycom HDX 9004,
> Tandberg T3 and the Mirial Softphone and all worked.
> Alessandro, which Polycom device causes you trouble ? Is the new
> plugin working any better there ?

So far only the Polycom VSX 5000: it was the first one I tried and it 
did not work, so I found a fix for it but have not tested it with other 
devices yet.

In any case the fix makes sense: resetting the sbit to 0 produces a 
packet stream that is RFC2032-compliant but the resulting bitstream is 
not H.261-compliant, that is it is decodable only by an RFC-aware 

However H261Encoder::sbit_ seems to never be initialized to a know 
value, so it is possible that (depending on machine, build type and 
alignment of the Moon in Pisces) the initial value falls outside the 
0..7 range and nothing will work.

Can you try to add

, sbit_(0)

(including the leading comma) to the list of initializers of 
H261Encoder::H261Encoder() (the very first function defined in 


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