Video over IP

H.239 in Video Conferencing – Share Data and Presentations along with Video

The above video is a demo video for something else, but they do show glimpses of how two monitors can be connected to a video conferencing system, where one displays video and another displays data/presentation. Sorry, I didn’t get a video specific to H.239!

What is H.239 in Video Conferencing?

H.239 is a standard to share data/presentations/second video channel along with the primary video channel. That means, while you can see and talk to people from remote locations using video conferencing technology, you can also share your computer monitor output or a document camera output to the participants on the remote end. The person who is talking can show a presentation/ graphic file from their computer, to remote conference participants. This enables people to understand the context of discussion better.

H.239 basically enables a video conference system to send two streams of media together. So, either video is combined with computer monitor output (data/presentation) or an auxiliary video source and sent to the other end, which can divide them into two separate streams and display them separately. People on the remote remote end can view the computer monitor/document output connected on the other side, LIVE. If a cursor is moved from one location on the computer screen to another (for example), the people on the remote end will be able to see it in real-time.

Each VC system supports a certain maximum resolution for data transfer (Like HD, XGA, SVGA, etc). Since two streams of media are transmitted with H.239, some additional bandwidth is occupied but the maximum bandwidth limit for the data stream can be set in many video conference systems.

Which media sources can be connected to a video conference system & shared with the remote end?

Many video conference systems support a PC/laptop to be connected to it (over a VGA/DVI cable).  Some of them can even connect to a document camera/DVD player/second (auxiliary) camera, etc and send their output to other end. These additional multimedia streams are sent along with the main video output of the video conference system.

How do people at the remote end view the data/presentations/auxiliary video?

Depending on the make and model of the video conferencing system, there are many ways to view the second media stream. The best way is to have two different monitors or one monitor + one projector connected to the VC system and display the main video (people) on one of them and display the data/presentations on the other. This enables people to easily see both outputs clearly.

But some video conferencing systems do not support two monitors to be connected to them. In such cases, people can use a single monitor but they need to toggle between the video and data using their remote control or they can view them side by side on the same screen (screen is divided into two parts).

Some VC systems support picture in picture feature which lets the users see the presentation on the main screen and the people (main video) on a small box on one corner of the same screen. There are multiple customizations available for these options.

How does one enable H.239 in their VC system?

While most of the video conferencing systems meant for enterprises support H.239, a few models may not. So, its better to check before-hand. Many VC systems support this feature natively but some of them require additional software licenses or additional hardware units to enable H.239 (at additional cost).

Once this feature is enabled, it is just a question of connecting a media source and sharing its output by pressing a key on the remote control. It is better if both the video conferencing systems that want to use H.239 are manufactured by the same vendor. But it is possible to use it, even otherwise.


Since H.239 is a standard, the data sharing capability of the VC system is supposed to work even if there are different brands of video conferencing equipments at either end. While this is possible, there are factors like make, model, firmware version, license and other factors that can hinder VC models manufactured by different vendors to share data/content using H.239.

H.239 is supposed to be compatible with Video Conferencing systems connected over both IP and ISDN networks. In case of Multi-Conference system (video conference between 3 or more locations simultaneously), a user present at one location can connect their laptop and send the data/presentation, which is received by all the participants. Of course, there are some limitations in these cases.

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  • Rinka

    Here’s a brief comparison of H.329 vs the T.120 suite
    The T.120 suite is older, looks like it’s richer (H.329 allows for sync between video & data) and (because it’s older) is integrated into far more products (the NetMeeting for example).

    Would you like to comment on the additional value that H.329 brings to the table that T.120 doesn’t?

    • admin

      I don’t know much about T.120. Let me look at some resources and try to do a separate article on the same. Thanks for bringing this to my notice.