[h323plus] H323-SIP Gateway with H264 Support

[Diego Carvalho]

Hi Simon and "chr_cb". First of all, thanks for your help. Today I was able
to establish an audio only call between H323 and SIP using the gateway I'm
developing. This is great but I still have some problems and I appreciate
any help on this:
1) Like I said, it was an audio only call. I was able to compile the
plugins with the packages from Ubuntu repositories (libx264-dev,
libavcodec-dev and libavutil-dev) but my project also uses ffmpeg and x264
so I would like to compile with the latest source code from git we use. The
config.log shows some errors and on the internet I saw somebody saying that
only a specific version of ffmpeg allows the compilation. Is that true? If
so, what would be the version of ffmpeg and x264 I should use? Again, I
would like to reiterate that I only want to have H264 on my capabilities
list (I don't want to capture/render video). Do I indeed need the plugin?
Is there another way?
2) If I set the gateway capabilities in the beginning it works but I want
so set them in a later time. Specifically, I receive the call and send an
invite on hold to SIP. Then it will answer with 200 OK with SDP. In this
moment, when I have the SIP SDP, I want to set the gateway capabilities
based on what the SIP side supports. How can I do this? If I try to add in
this moment it simply doesn't add them.
Thanks in advance.

2012/3/13 Simon Horne <s.horne at packetizer.com>

> Diego
>
> The plugins load default capability instances into the H323Endpoint.
> When the H323Connection is created these capabilities are cloned
> In H323Connection::OnSetLocalCapabilities()
> Simply remove the unmatched capabilities
> localCapabilities.Remove("H.264*");
>
> The H323_ExternalRTPChannel does not handle RTP but can be used to not use
> the internal RTP system. You can have your own external RTP stack or not
> have one at all.
> You needed to read and populate H245_H2250LogicalChannelParameters in the
> send and receive message of the class with those of the SIP Client.
>
> I do have serious doubts what you are planning will work not because it
> can't technically work but because of the differences in H.323 and SIP with
> Video. H.323 is very strict on rules while SIP is very loose on
> interpretations.
> Here are the problems
> 1. RTP packetization H.323 says strictly single NAL SIP is undefined 2
> options (Single NAL/Fragmented units) . You will get video on the H.323
> side
> just fine but your SIP side with some devices may not be able to decode.
> 2. Payload Type for H.264 is specified as being flexible but a lot of SIP
> implementations have them fixed (usually 96 or 97) so H.323 requests 103
> SIP always ends 97  no video on the H.323 side. There is no way you can fix
> this with signaling as SIP tells the other party what it is going to send
> and H.323 tells the party what it wants to receive. You have to proxy the
> media to fix the payload type number.
>
> Good luck.
>
> Simon
>
>
> ============================================================================
> =============================================
>
> From: Diego Carvalho [mailto:diego.cdomingos2010 at gmail.com]
> Sent: 14 March 2012 06:09
> To: Simon Horne
> Subject: Re: [h323plus] H323-SIP Gateway with H264 Support
>
> Hi Simon, thanks for answering but I still have some doubts:
> You said that this plugin will add the capability automatically. Actually,
> as I said, I'm building a H323-SIP gateway so, for instance, when the SIP
> endpoint is making a call I want to add the H264 capability only if the SIP
> endpoint offers it. Will I be able to add the capability manually? For
> instance, using localCapabilities.Add(new H323_H264Capability()). To
> sumarize, I want to be able to add (or remove if it was automatically added
> and the current call does not offer it) manualy the H264 capability.
> Also I don't know if the H323_ExternalRTPChannel applies to my situation.
> It's used to pass the RTP to another device. I don't want to handle the RTP
> at all (to be clear: I don't want RTP arriving on the gateway's network
> card). I want to send to h323 the RTP address/port SIP offered and
> vice-versa, so the RTP will flow directly between the endpoints. Any
> thoughts? Thanks in advance.
> 2012/3/13 Simon Horne <s.horne at packetizer.com>
> Diego
>
> H.264 is a video plugin in the plugin/video directory. You will need X264
> and FFMPEG.  For Ubuntu they are libx264-dev  libavcodec-dev and
> libavutil-dev.
>
> You build the plugin .so and the helper (in the gpl subdirectory) and place
> them both in the same directory as you app. The application will load them
> at startup and automatically add the capability to the capabilityset etc
>
> If you don’t want to use the plugin for RTP then have a look at the
> H323_ExternalRTPChannel. This will bypass the RTP handling in the codec to
> whatever you want.
> http://www.voxgratia.org/docs/external_rtp.html
> (its from 2004 but still current)
>
> Simon
>
>
> From: h323plus-bounces at lists.packetizer.com
> [mailto:h323plus-bounces at lists.packetizer.com] On Behalf Of Diego Carvalho
> Sent: 14 March 2012 03:05
> To: h323plus at lists.packetizer.com
> Subject: [h323plus] H323-SIP Gateway with H264 Support
>
> Hi all,
> I'm working on a h323-sip gateway with video (H264) support and I'm facing
> some problems. I'm new with H323plus and with h323 protocol itself (I'm
> learning as I go) so excuse me if I say something stupid.
> First of all, I believe that the stack can be used to build a gateway but
> it
> seems that it's more focused on terminals. Am I right? So is it possible or
> not to build a gateway using it?
> Second, there is no native support for H264. The documentation shows the
> class hierarchy. For audio we have, for instance, H323Cabability ->
> H323RealTimeCapability -> H323AudioCapability -> H323_G711Cabability but we
> don't have H323Cabability -> H323RealTimeCapability -> H323VideoCapability
> -> H323_H264Cabability. I tried to create this one, extending from
> H323Cabability -> H323RealTimeCapability -> H323VideoCapability ->
> H323GenericVideoCabability and then I discovered that I would need to
> override a function called CreateCodec to return a codec that handles the
> video. But I don't want to handle the RTP media. I just want to put H264 in
> the terminal capability set and establish a connection in a way that the
> H323 and SIP terminals can exchange the media directly. I've heard about a
> H264 plugin but it seems that it is for handling the media, so I don't know
> if it fits my purpose. How can I achieve this? Is there any plan to support
> H264 natively on H323plus? Also I need to get the remote RTP port. The only
> way I found to do this is trough H323Connection::OnStartLocicalChannel but
> this is called after a channel to handle the data is created and again, I
> don't want to handle the RTP data. I appreciate any help. Thanks.
>
>
>
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