So, in the process of trying to help a colleague find a way to add HDMI support to an existing 5-BNC RGBHV switching system, I’m reminded of just how poor the state of EDID handling is on A/V equipment.

Essentially, my colleague needs an HDMI-to-VGA converter so he can feed the resulting signal into his RGBHV matrix switch. If problem with this setup is EDID handling. In an RGBHV system, there’s no DDC signal and, hence, no EDID information can be passed to the computer. This has all kinds of bad results, ranging from the computer not detecting the connection at all, to being unable to select the right output resolution, to (on Macs, particularly) getting an output picture that’s horizontally compressed due to aspect ratio mis-match.

Why can’t equipment vendors consider EDID processing and, even more importantly, publish their device’s EDID capability in their manuals? I have to resort to buying 5 different devices and testing their EDID handling and sending most (or all) of them back when I discover that they do the wrong thing.

So, what’s the wrong thing? Well, on HDMI-to-whatever devices, it’s usually one of:

• No EDID handling whatsoever (they send no EDID at all)
• Sending a hard-coded “1080p” EDID regardless of the sink device or output resolution (I’m looking at you, Kramer Electronics; and you Aurora Multimedia)
• Passing most of the sink device’s EDID, but adding in extra resolutions that don’t match the sink device’s aspect ratio

Any one of these common flaws results in an unusable connection.

And this is especially true of Mac systems. For some reason, they always re-format their output to match the aspect ratio of the connected device. If the device says it supports 1080p or any other 16:9 resolution, and you switch your output resolution to, say 1024×768, the Mac will add black bars to the side to pad out the video to 16:9! Then, your XGA projector shows a tall, squished picture on the screen even though you selected the right resolution manually. Why, Apple? Why?

So, the moral of this story is: Always make sure your EDID is handled correctly. (And have lots of EDID emulators on hand for when it’s not 🙁 )