[h323plus] Video Resolution

Carlos Haj unazona at hotmail.com
Fri Jan 15 12:24:11 EST 2010


I used fixed width and height to determine display and reader working, and I traced again my application.

This time I went deeper into the h323plus library, I think it's a bug
of h323plus, between the library and the video codec plugin.

Bug Scenario:

I have set 

    AddAllCapabilities(0, P_MAX_INDEX, "*");

I only use H261 this time


Set the maximum Frame size and send a kind of parameter cifTag to the plugin

on my OnVideoChannel I initialise 

if (encoder) 

       codec.SetFrameSize(176, 144);

This is the call stack by chronological order for an h323 video call
using a CIF<->QCIF endpoint (trace is for endpoint that sending

1) H323PluginVideoCodec::H323PluginVideoCodec(...)

it creates the encoder, and set frame size to CIF (the default plugin maximum value)

2) H323PluginVideoCodec::SetFrameSize(...)

it adjusts the frame size, called from my OnVideoChannel, with qcif Value

3) H323PluginVideoCodec::Read(...)

All work, my rawChannel, renderer, etc... until I reach line 1690

H323pluginmgr.cxx::1690 - THE FIRST READ call to encode video fails

    int retval = (codec->codecFunction)(codec, context, 

                                        bufferRTP.GetPointer(), &fromLen,

                                        dst.GetPointer(), &toLen,


retval = 0, which results into closing the channel as it returns false,

if I change SetVideoFrameSize(H323Capability::cifMPI); into SetVideoFrameSize(H323Capability::qcifMPI);

The codec function works again, but naturally with qCIF on both sides

I think that once the codec parameter was tagged to use a cif or a qcif
it can't change resolution during the call. so the encoding function
fail for a resolution different than one setted using the

It's likely that the SetVideoFrameSize send an additional information
to plugin code using a setcontrolcodec which are required later so the
encoding function works properly.

I noticed, that video resolution fail is only a local behaviour, and has nothing to do with remote endpoint.

I will be debugging more, I still don't know the plugin code so much,
so you might have a clearer idea than me? I think if you make a simple
test you would encounter the same behaviour!


From: s.horne at packetizer.com
To: unazona at hotmail.com; h323plus at lists.packetizer.com
Subject: RE: [h323plus] Video Resolution
Date: Sat, 16 Jan 2010 01:37:07 +1000

You cannot know what the remote will send when you call 
OpenVideoChannel for the decoding side, that can only be done when you 
receive the first RTP packets. 
You need to do a level 6 trace to work out who and why the 
channel is being closed. I don't think it is a capability issue, usually the 
problem comes from either the video encoder device (webcam) or the display 
device. Check to see that you have set the video input device to 
send at the same size as your encoder. The old openH323 used 
to do be able to do that automatically as the frame size for the 
capability was known. You have to make sure the input 
to the encoder from the webcam is correct.  
Version of h323plus would be irrelevent in this case. 


From: Carlos Haj [mailto:unazona at hotmail.com] 

Sent: Saturday, 16 January 2010 1:06 AM
s.horne at spranto.com.au; s.horne at packetizer.com; 
h323plus at lists.packetizer.com
Subject: RE: [h323plus] Video 


Thanks for valuable information. What is happening 
literally in a minimised case: I derived OnVideoChannel

on the Local 

if (encoding)
codec.SetFrameSize(352, 288);
      cout << 
      cout << 
      // I receive CIF 

on the Remote 

if (encoding)
codec.SetFrameSize(176, 144);
      cout << 
      cout << 
      // I receive 
CIF (normal)

I looked into H323 trace Log, 
(remote endpoint which supposed to send QCIF) 

PLUGIN       Error encoding frame from 
plugin H.261-CIF
Request CloseLogicalChannel
H323RTP     Transmit 
H.261-CIF thread ended

It seems that the H.261 channel is closed 
prematurely. As my local endpoint received an incorrect video size I suppose 
that local endpoint causes remote to close the transmission 

Could this be related to the version of the plugin or h323plus 
lib which I use? it's likely that the video resolution is sent before 
codec.SetFrameSize is invoked!

Did you in practice used different video 
resolution under the same capability? e.g. CIF<->QCIF 


From: s.horne at spranto.com.au
To: unazona at hotmail.com; s.horne at packetizer.com; 
h323plus at lists.packetizer.com
Subject: RE: [h323plus] Video 
Date: Fri, 15 Jan 2010 23:14:23 +1000

The current behaviour is correct. 
The old OpenH323 used to only send CIF with *-CIF{sw} 
capability and only QCIF with *-QCIF{sw} . This was 
changed with the video plugins so the capability could do up to CIF so 
it would also supported QCIF. This is perfectly 
H.245 legal.
In this way only 1 capability can do both frame sizes. 
This is the way most manufacturers implement the capability 
The capability has a flag for the size it supports so the old CIF 
capability used to say QCIF - 0 CIF - 1. So if you wanted to do QCIF you 
had to use the *-QCIF{sw} capability as the QCIF flag in the *-CIF{sw} was 0. 
This was changed so that the *-CIF{sw} capability had the QCIF flag so it could 
also support QCIF. Then it was safe to remove the *-QCIF{sw} capability and only 
exchange using the *-CIF{sw}. 
Now SetVideoFrameSize() will set the global frame size limit so 
regardless of the direction that will be the maximum size permitted (if CIF 
only up to CIF capability is available). The codec.FrameSize() in the 
MyH323Endpoint::OpenVideoChannel() allows the implementor to set the 
actual frame size to send. 
Is there something else I missed?

From: Carlos Haj [mailto:unazona at hotmail.com] 

Sent: Friday, 15 January 2010 8:39 PM
s.horne at packetizer.com; h323plus at lists.packetizer.com
Subject: RE: 
[h323plus] Video Resolution


Thanks for your quick answer, just noticed that I had a 
bad thread name;)

Well, I have the codec.SetFrameSize(w, h); in my 

When adding capabilities I 

AddAllCapabilities(0, P_MAX_INDEX, 

table shows as 

Set 0: 0: 

I receive an OpenVideoChannel for encoder, I open 
channel and attach video reader + colourConverter, just after that I receive a 
close video signal from a H245Negotation, here I join Call Stack

>   testApp.exe!mmDDSVideoOutputBridge::close2()  Ligne 
359    C++
testApp.exe!mmVideoInputDevice::~mmVideoInputDevice()  Ligne 43 + 
0x1b    C++
testApp.exe!mmVideoInputDevice::`scalar deleting destructor'()  + 
0x2b    C++
testApp.exe!PVideoChannel::CloseVideoReader()  Ligne 203 + 
0x24    C++
testApp.exe!PVideoChannel::Close()  Ligne 145    
testApp.exe!H323Codec::CloseRawDataChannel()  Ligne 488 + 
0x11    C++
testApp.exe!H323VideoCodec::Close()  Ligne 747    
testApp.exe!H323Channel::CleanUpOnTermination()  Ligne 
716    C++
testApp.exe!H323_RTPChannel::CleanUpOnTermination()  Ligne 
1160    C++
testApp.exe!H245NegLogicalChannel::Release()  Ligne 1219    
H245_CloseLogicalChannelAck & __formal={...})  Ligne 
1086    C++
H245_CloseLogicalChannelAck & pdu={...})  Ligne 1372 + 
0xf    C++
testApp.exe!H323Connection::OnH245Response(const H323ControlPDU & 
pdu={...})  Ligne 3293 + 0x22    C++
testApp.exe!H323Connection::HandleControlPDU(const H323ControlPDU & 
pdu={...})  Ligne 3189 + 0x12    C++
testApp.exe!H323Connection::HandleControlData(PPER_Stream & 
strm={...})  Ligne 3170 + 0x18    C++
testApp.exe!H323Connection::HandleReceivedControlPDU(bool readStatus=true, 
PPER_Stream & strm={...})  Ligne 3103 + 0x12    
testApp.exe!H323Connection::HandleControlChannel()  Ligne 3085 + 
0x13    C++
testApp.exe!H245TransportThread::Main()  Ligne 700    

If I remove the 
"SetVideoFrameSize(H323Capability::cifMPI);", I get the following capabilities 

1: H.261-CIF{sw}

with exactly same 
strange behaviour, QCIF is not sending while CIF is being received, by the way 
qcif endpoint says

Local Video Codec - H.261-CIF{sw}
Local Resolution 
- 176x144

Remote Video Codec - H.261-CIF{sw}
Remote Resolution - 

I tried a "ReorderCapabilities(PStringArray("QCIF"));" after 
my addcapabilities, I ended up with both endpoints using QCIF and ignoring my 
SetFrameSize anyway!!

Is there a glitch using H323Plus video plugins? my 
code works perfectly on openh323 

"SetVideoFrameSize(H323Capability::cifMPI);" is supposed to define 
a maximum video resolution?! as you said in API doc "... to set the maximum 
framesize allowed to the specified value "

Is that usual to have 
H.261-CIF with a QCIF resolution? On which order codec plugins can be added to 
avoid such problems of negotiation?


From: s.horne at packetizer.com
To: unazona at hotmail.com; 
h323plus at lists.packetizer.com
Subject: RE: [h323plus] Valid sessionID in 
OpenLogicalChannel command
Date: Fri, 15 Jan 2010 08:12:54 +1000

In your 

From: h323plus-bounces at lists.packetizer.com 
[mailto:h323plus-bounces at lists.packetizer.com] On Behalf Of Carlos 
Sent: Friday, 15 January 2010 12:59 AM
h323plus at lists.packetizer.com
Subject: Re: [h323plus] Valid sessionID 
in OpenLogicalChannel command

Hello Guys,

I would like to have different frame sizes for two endpoints, 
first I tried to play around with H323Endpoint::SetVideoFrameSize, but it seems 
that part changes the maximum allowed size, which means that if I switch the 
videoFrameSize to qCIF, I wouldn't be able to receive CIF from the other 
endpoint. my test only received QCIF.

I tried also to modify the 
OpalMediaFormat by using a GetWritableMediaFormat for a capability, that ended 
with unusual CIF format while having a QCIF resolution.

On the other 
hand, I looked Opal examples where they use an OpalManager, but unfortuntly that 
seems incompatible with h323plus, while old openh323 tutorials and exampls don't 
have any video plugins support.

How I can manage to receive and send 
different resolutions (frame sizes) using H323plus?

I appreciate a lot 
your help

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