updated 12:52 am EST, Tue March 5, 2013
'HDMI' signal is actually compressed, but will improve with OS update
The teardown of Apple's Lightning-to-HDMI iPad mini adapter done by developers at Panic has revealed a bit of misleading advertising from Apple's product page for the adapter: while the adapter does indeed produce a 1080p image on a television, it has been compressed using H.264 -- resulting in some compression artifacts. While inferior to the previous (and cheaper) 30pin-to-HDMI adapter Apple still sells for older iOS devices, the problem is expected to be resolved in a future software update -- thanks to the Lightning adapter's future-proofing.
The root of the "issue" lies within Apple's decision to make the Lightning standard as future-proof as possible, leading it to include an ARM SoC (System on a Chip) processor inside the cable itself to handle decoding duties. This choice means that Lightning can adapt to any new interface that comes along (and a variety of older protocols) simply by making an adapter for it, since the adapter is programmed through firmware to do the decoding. This also means that if, for example, a new standard emerges for HDTV, current Lighting devices will not be affected by the change, adding to their useful lifespan.
However, at present the Lightning standard is "simply not capable of streaming a 'raw' HDMI signal across the cable," according to an "anonymous" commenter on Panic's blog who strongly hints he or she is an Apple or Intel employee working closely with the Lightning technology. "Lightning is a serial bus ... there is no clever wire multiplexing involved." Lightning cables use only eight pins compared to HDMI's 19 pins, according to the commenter. To accommodate future changes, Apple needs only to update the firmware on the adapters SoC chip and make an adapter for it.
The same commenter said that a decision was made for the time being that the compressed 1080p coming from the Lightning-HDMI adapter was "suitably acceptable," but that future iOS firmware updates should add support for true 1080p signals, along with improved streaming. Currently, the Lightning adapter can only handle up to 1600x900 rather than 1920x1080. The commenter indicated that Apple is well aware that "quality could be better" and that the issue is being addressed, though he or she didn't give any clues as to a timeframe for the needed firmware updates.