ClearOne Digital Media - Manual (Page 28)

Why transport stream DRM is problematic in multi-source
systems.
As is often the case with complex digital systems, particularly when DRM or digital
encryption technologies are involved, what should “just work” rarely does as promised
which is why a complete understanding of the pitfalls and challenges of multi-source and
multi-display video distribution must be understood.
To begin we need to define key elements contained within HDMI starting with the Data
Display Channel (DDC). The DDC is a two-way communications interface that sits between
the source and associated downstream repeater (or display device). The purpose of this
channel is to communicate device capability information encoded in a structure known
as Extended Display Identification Data (EDID). HDMI devices use EDID to broadcast to
receiving devices the audio and video formats supported. It should also be noted that the
DDC interface is used to set up and maintain HDCP encryption.
Adjacent to DDC is Hot Plug Detect (HPD), which broadcasts to downstream devices,
indicating its presence to the source. HPD allows each device to know when a cable has
been connected and automatically triggers authentication including EDID information about
a display to a source conveying its resolution capabilities.
Initially developed for computers and monitors, EDID is now found in most all consumer
electronic devices that support HDMI. As an example, a television may use EDID to indicate
support for the standard HD resolutions in addition to 1080p and Deep Color while another
TV may not support higher than 720p / 1080i resolution. All information regarding the audio
and video capabilities of each device is stored in its EDID.
The challenge AV professionals face in simple installations is minimal. In fact one could
argue HDMI greatly eases set-up and compatibility issues when dealing with simple
consumer systems comprising a single source and a single display. However, it is our
assumption the reader of this guide is commonly dealing with system designs of a much
more complex nature such as multi-room and multi-source, with perhaps dozens of displays
needing to be switched reliably. And for these system design applications, StreamNet was
developed.
pg 28 StreamNet Digital Media and System Design Reference Guide
Digital File Security and DRM