2009-11-05

HDMI-CEC is SLOOOOOOOOOOOOOW!!!

Well, like many, I was convinced that HDMI-CEC was the wave of the future with regards to AV automation, until I actually read the specs of the thing (in "Supplement 1 Consumer Electronics Control (CEC)" of the HDMI Specifications version 1.3a).
The interesting bits are to be found in "CEC 5 Signaling and Bit Timings" and "CEC 6 Frame Description", where, if you do the maths, you actually find out that the shortest time it takes to transfer a single 8 bit packet (start bit + 10 bit header + 10 bit packet) is 52.5 ms. And if you were to transfer 32 bits of data, you get close to 125 ms, or, in other words, no more than eight 32 bit data packets per second.
Heck, I can mash a remote button faster than that!

What this means really is that. no matter how cool HDMI-CEC might look, with a max data rate of only 41 bytes per second, future proof it ain't.
Thinking of transferring a GUI menu content from one device to another using CEC? Won't happen.
Thinking of transferring a reasonable amount of text in a short time? Nuh-huh.

For a format designed in 2002 to be more than 20 times slower than what has been the de-facto lowest speed for any form of serial data communication (9600 bauds) for more than 30 years now, you really got to be kidding us.
And it's not like either the cable or devices connected can't support high transmission speed (it's HDMI - both the cable, and the devices it connects were designed for high speed!).

So really there you have it. On one hand, a handful of transmission lines that can transfer at least half a Gigabyte of data per second, and in the same cable, a puny line that will barely transfer 1/1,000,000th of it, because of our regular corporate overlords' lack of vision (guys: if you're going to borrow what SCART has been doing for more than 2 decades, at least bring it up to speed).

Oh the irony!

1 comment:

  1. Couldn't agree more. It really is pathetic and very frustrating :-(. If there's one thing that drives me crazy it's a sluggish remote/gui on an HTPC or STB.

    http://blog.rhysgoodwin.com/

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