The app_h324m application will allow to bridge the h223 multiplexed channel to a local asterisk channel that will be routed again to the pbx core following the configured dialplan, converting the Asterisk server in a 3G-H324m Video Gateway.
The following diagram shows the architecture of the final solution that will enable a 3G mobile handset to establish a UMTS video call with a Video Softphone IP.
The 3G Gateway is connected to a ISDN E1 interface and with an IP PBX. It will handle both the SIP and H245 negotiations to establish the two legs of the communication, one with the 3G handset and the other with the Video Softphone. When the communication is establish it will mux and demux the h223 video call data from the 3G handset to be able to bridge the audio and video between the endpoints performing the necessary transcoding operations needed to meet the endpoint capabilities.
The 3G gateway will be implemented as an application to the Asterisk PBX and use the other Asterisk applications to provide all the required functionality.
The library will handle the h245 negotiation with the 3G handset and establish both audio and video streams. Media streams will be bridged together and forwarded from one channel to another, multiplexing or demultiplexing in each case.
Video calls require a special media formats and codecs. Audio will be passed through an AMR codec to encode it before sending to the 3G handset and to decode the reverse stream to allow asterisk to handle it. Video sent to the 3G handset needs to be rescaled to QCIF size and transcoded to fit in 52Kbits.
You can download the documentetion from here