Apple's Lightning-to-HDMI adapter and the product page for the iPad mini claims that the device is able to output 1080p images to televisions. But that may not be strictly true, according to some research from developers over at Panic. They've discovered two separate-but-related issues with the claim: first, the Lightning version of the adapter only supports an output resolution of 1600×900 from the iPad mini, not 1920×1080 as advertised. The second is that the output is full of visual artifacts consistent with signals that have been compressed and sent to a TV though Apple's AirPlay feature.

The Panic Blog proceeded to tear one of Apple's adapters apart and, with the help of an anonymous commenter purporting to be an Apple employee, figured out what was going on: the iDevice is actually sending an H.264-encoded image through the Lightning interface to the adapter, where a small ARM chip decodes that information and outputs it over HDMI.

"The reason why this adapter exists is because Lightning is simply not capable of streaming a 'raw' HDMI signal across the cable," said the supposed Apple employee. "Lightning is a serial bus. There is no clever wire multiplexing involved."

The upside of this approach is that it shifts the complexities of supporting new output interfaces away from the device and to the cable itself—if something comes along and replaces HDMI (or if you want to connect to another existing interface, like DVI or even GPIB), you won't need to throw out your expensive device and get a new one to get support. Apple just has to update its software to support the interface and make an appropriate adapter to supply the hardware, since the adapter is the piece that's actually responsible for handling output.

One downside of this approach is that it's going to result in more costly adapters for consumers—the Lightning-to-HDMI adapter in question costs $49 on the Apple store, where the older 30-pin-to-HDMI adapter costs $39. Another is that, at least for now, the image quality and resolution delivered by the Lightning version of the adapter is lesser than that provided by the older 30-pin version of the cable. However, future iOS updates should be able to add true 1080p resolution support to the adapter as well as improved streaming quality.

"Certain people are aware that the quality could be better and others are working on it," said the Panic Blog's anonymous commenter. "For the time being, the quality was deemed to be suitably acceptable."