Can you identify a particular HDTV screen or

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Can you identify a particular HDTV screen or screen vendor over HDMI without HDCP?

Can you identify a particular HDTV screen or screen vendor over HDMI without HDCP? Tim Wright Sept 2010 Version 0. 1

How are screens/Sinks identified? • See chapter 8, Control and Configuration, of the HDMI

How are screens/Sinks identified? • See chapter 8, Control and Configuration, of the HDMI spec: – HDMI has 3 separate channels: TDMS, DDC, CEC • TDMS takes all the AV data • DDC is the control channel • Optional CEC channel is optional extensions – We are interested in the DDC channel – Sink is identified/characterised over DDC using the Sink’s EEDID structure (Enhanced Extended Display Identification Data Standard)

What’s in the E-EDID? • For HDMI, the E-EDID must contain as its first

What’s in the E-EDID? • For HDMI, the E-EDID must contain as its first extension a version 3 CEA Extension (see section 8. 3. 1) • This extension must include an HDMI Vendor-Specific Datablock (VSDB) • VSDB contain – – Vendor-specific tag (=3 in all cases) IEEE Registration Identifier Physical address Various field describing the AV capabilities (caps) of the Sink

Is the physical address useful? No • E-EDID contains the Sink’s physical address •

Is the physical address useful? No • E-EDID contains the Sink’s physical address • But this address is generated by the Sink itself and is not a reliable indicator – It merely indicates the Sink’s position in Repeater-Sink chain • So if the Sink is the last link, then the physical address is 0. 0 • See HDMI spec, section 8. 7

Is the IEEE Registration Identifier useful? No • E-EDID contains the 24 bit IEEE

Is the IEEE Registration Identifier useful? No • E-EDID contains the 24 bit IEEE Registration Identifier • But this merely indicates if the Sink is HDMI or not – HDMI has an IEEE Registration Id of 0 x 000 C 03 and Source must assume Sink is DVI if its not HDMI

Are the AV descriptor fields useful? Yes • These fields describe the AV caps

Are the AV descriptor fields useful? Yes • These fields describe the AV caps of the Sink: – – – Picture aspect ratio Colorimetry Scan information Quantization range Other stuff • Its very unlikely that these values will be the same across the standard Sink (e. g. an HDTV) and a capture device (e. g. a PC) – PC could spoof the values of the screen, but would need to know them, and risks not being able to function correctly by using descriptor values that do not actually describe its real caps • Change of AV descriptor fields can therefore be a reasonable reliable indication that the Sink has changed from the normal Sink to a capture device

Conclusion • There is no reliable way to identify a particular screen/HDMI Sink without

Conclusion • There is no reliable way to identify a particular screen/HDMI Sink without HDCP • But you can identify that the Sink has changed