EDID and capabilities

CDS

Capability Data Structure, the eARC equivalent of EDID

An eARC connection does not read an EDID the way an ordinary HDMI source does. It is handed a Capability Data Structure instead, and that is what decides which formats a TV will send back down the cable.

CDS stands for Capability Data Structure. It is the list of audio capabilities that the device receiving eARC audio, an AVR, a soundbar or a box like this one, presents to the eARC transmitter at the other end, which is normally the television. It does the job an EDID does everywhere else in HDMI, but by a different route: an EDID is read out of a memory in the display by whatever is plugged into it, while a CDS is exchanged over the dedicated eARC data channel and can be updated when capabilities change.

The contents are the same currency as the audio part of an EDID. Short Audio Descriptors name each format the receiver can decode, with channel counts and sample rates, alongside speaker allocation and a few capability flags. That is how a television knows it may send Dolby Atmos over TrueHD to one soundbar and no more than Dolby Digital to another. The reason eARC needed its own structure at all is bandwidth: the old ARC return path could not carry the formats the new one can, so both ends had to be able to state exactly what they support.

eARC and CDS on the HDfury Diva

Nothing in the Diva web server is labelled CDS and there is no editor for it. What the manual describes is the result. With a television whose eARC capable input is connected to TX0, the Diva extracts up to Dolby Atmos HBR over TrueHD from it and forwards that to the dedicated HDMI audio output, which can then feed any AVR input able to decode the format. Extraction happens automatically, and because eARC does not rely on CEC you do not need to select any CEC option to get it.

The routing rule that follows catches people out. CEC, ARC and eARC master is TX0, so the television you want sound from belongs on TX0 whichever display you consider primary, with TX1 left for a second, older 1080p SDR set. The AVR then sits on the HDMI audio output rather than in the video chain.

What you control instead

For a television with ARC rather than eARC there is no capability structure involved at all: that path is CEC based, handles up to DD+ and Atmos over DD+, and needs ENABLE CEC ticked, the CEC device type set to Audio Processor in the CEC and RS232 section, and Enable DD+/ATMOS ARC if your AVR can take it. Over IP those are set cec on, set cecla audio and set archbr on.

All glossary terms