The search for the truth behind Apple’s Lightning digital AV adapter

Sending video from your phone or tablet to your TV is a very useful ability, and many options exist for doing so wirelessly – though most existing solutions are highly compressed and quite laggy. Obviously, a wired connection is what’s needed, right?

If you want a crisp 1080p signal from your iPhone or iPad, the best bet is to plug it in directly using Apple’s own £39 Lightning digital AV adapter. Unfortunately, it seems that this latest iteration of the device – designed to work with the new Lightning connector – isn’t putting out full 1080p.

Even worse, it seems that it is introducing noticeable compression artifacts (pictured below). Now comes the search for the truth amongst all of the Internet rage this is kicking up among Apple enthusiasts.

Cabel Sasser, a well-known software developer at Panic Inc., brought this issue to light at the end of last week. Through his own testing, he discovered that using the old Dock Connector AV adapter will output a full 1920 x 1080 video mirroring signal, but the newer Lightning AV adapter tops out at 1600 x 900.

After taking a hacksaw to the tiny adapter, it’s apparent that this isn’t just a simple cable. In fact, it has a minuscule ARM SoC and it is sporting upwards of 256MB of RAM. Cabel theorises that it is employing the same compression used in AirPlay to stream out the video, and that would explain the lag and artifacts being introduced to the signal. But why bother with this middleman at all? Well, we don’t have an official answer from Apple, but we have the next best thing: Wild conjecture and anonymous comments.

The Internet exploded with countless rage-posts about how Apple is screwing consumers. As cathartic as that may be, it didn’t provide much insight. Luckily, a comment on the original post provides interesting background to the ordeal. The anonymous commenter gives plenty of detail, and hints heavily that he or she is an Apple engineer. The commenter confirms that the SoC boots into Apple’s XNU kernel, but that’s as close as it gets to being iOS-like. Lightning isn’t capable of outputting an HDMI signal, so instead of adding complexity to each device, HDMI functionality was moved into the adapter.

According to this explanation, the iPhone uses the same hardware H.264 encoding that it would use to send video wirelessly over AirPlay. It then sends that compressed data out of the Lightning serial bus, and directly to the adapter. The SoC decodes the video, and handles the rest of the trip out to the end of the HDMI plug.

This accounts for all of the problems that Cabel ran into, and it seemingly has an understandable reason for existing in the first place. By having the iPhone spit a vanilla H.264 signal out of the Lightning connector, countless adapters can be made to work with existing phones instead of relying on the phone itself to support different specs (like HDMI itself). All of the heavy lifting is done by the adapter.

The quality is a problem, but updates are certainly a possibility if this commenter is to be believed. He or she even goes as far as to claim that iOS updates on the phone or tablet will be able to improve the quality of the output. At least it won’t require you to shell out for a whole new phone or £39 adapter. This isn’t a good excuse for the low quality output, but at least improvement seems inevitable and free of additional cost. Now we just have to wait for Apple to get round to making this better.