H323plus does not call to_customise_options function. This is only for Opal.

Simon

From: h323plus-bounces@lists.packetizer.com [mailto:h323plus-bounces@lists.packetizer.com] On Behalf Of Vladimir Fekete
Sent: 25 February 2011 23:33
To: opalvoip-devel@lists.sourceforge.net
Cc: h323plus@lists.packetizer.com
Subject: [h323plus] "possible" bug in H323plus video codec for h.264

Hello all,

 I've been playing with h.264-x264 plugin for a while and since I had no problems between h323plus vs h323plus nor OpenPhone 3.8.3 application I do have problems with 

video codec h.264 for h323 from recent h323 plus  (e.g. version 1.22.0, 01/11/2011)

and 

application based on recent opal (rev. 25192)

I say "possible" because - as was said from few recent mails on mailing lists, opal and h323+ have similar root but they don't share plugins (necessarily). Nevertheless, when I tried to make a connection from OPAL application to h323+ based application, where both used h264-x264 plugin from h323plus video codecs (v. 1.22.0), my opal application crashed. 

I traced down the problem and fixed the lines in h264-x264.cxx and now it works for me.

Problem was following :

during the codec options set stage a method of OpalPluginMediaFormatInternal class is called. This one (opalpluginmgr.cxx)

bool OpalPluginMediaFormatInternal::AdjustOptions(OpalMediaFormatInternal & fmt, OpalPluginControl & control) const

call was made from void H323Capabilities::BuildPDU(const H323Connection & connection,  H245_TerminalCapabilitySet & pdu) const

line n.2706 (capability.GetWritableMediaFormat().ToCustomisedOptions();) in h323caps.cxx

in method AdjustOptions there are 2 variables set inside :

    char ** input = fmt.GetOptions().ToCharArray(false);

    char ** output = input;

and yes there are set *correctly*

they are immediately followed by this line (in my case line n. 477 in opalpluginmgr.cxx)

    bool ok = control.Call(&output, sizeof(output)) != 0;

which calls (opalpluginmgr.h)

    int  OpalPluginControl::Call(void * parm, unsigned   parmLen, void * context = NULL) const

and that one calls 

    int OpalPluginControl::Call(void * parm, unsigned * parmLen, void * context = NULL) const

(these 2 methods are not same, difference is in the second parameter, one is not a pointer other is) and this second Call(..) calls to_customised_options from h264_x264.cxx

    static int to_customised_options(const struct PluginCodec_Definition * codec, void * _context, const char *, void * parm, unsigned * parmLen)

and there is a line (in my case 837)

    const char ** option = (const char **)parm;

and here is the problem. if you look at the chain :

    AdjustOptions > Call > the "other" Call > to_customised_options

then you see that the output variable is transfered as :

   AdjustOptions               &output    char***

   Call                              parm        void *

   Call                              parm        void *

   to_customised_options  parm        void*

so in the end, parm is char *** and not char ** and this caused the crash

 How I fixed it 

changed "to_custoimized_options", file h323plus/plugins/video/H.264/h264-x264.cxx, line number 837

   const char ** option = (const char **)parm;

to

   const char ** option = *((const char ***)parm);

and also (same function, same file, line 858)

    char ** options = (char **)parm;

to

    char ** options = *((char ***)parm);

recompiled h264 plugin and it works.

Best regards,

 Vladimir Fekete

P.S.  I don't want to call it a bug because I'm not sure whether it's valid to mix h323plus codecs with opal (eg. separately they may work ok).