[h323plus] H.261 and G.722

Alessandro Angeli packetizer.com at riseoftheants.com
Fri Jan 7 17:19:52 EST 2011

The H.261 VIC codec does not work with hardware devices like Polycom's. 
The device complains about invalid sbit/ebit values.

The codec resets the sbit to 0 on a new picture, introducing an apparent 
discontinuity in the bitstream. However the device expects the bitstream 
to be continuos (prev.ebit + this.sbit = 8).

The fix is quite simple: just comment out 
H261PixelEncoder::PreIncEncodeSetup() { ... sbit_ = 0; ... } in 

The G.722 codec is never initialized. The codec reports a format of 
"PCM-16-16kHz" (L16Desc[] in "opal\plugins\audio\G722\g722codec.c") 
while the plugin manager only accepts "L16" 
(H323PluginCodecManager::RegisterCodecs() in 

Shouldn't the codec report "L16" in the 8 kHz descriptor? Or is there a 
deeper issue? Replacing "PCM-16-16kHz" with "L16" enables the decoder 
but not the encoder and the decoder doesn't decode anything.

G.722.2 seems to have the same issue.


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