Lightning to Digital AV adapter could be pushing lower res H.264 because it's not yet capable of streaming raw HDMI
Earlier today we linked to a post by Cabel Sasser on the Panic Blog about Apple's Lightning Digital AV connector, which is basically their HDMI adapter. Sasser had discovered that the adapter provided a less-than-1080p signal, broke it open, and found a tiny computer contained inside. Lots of speculation followed as to why that was, and what might be going on. A comment left on the Panic Blog by "Anonymous Coward", however, implies internal Apple knowledge of the matter, and purports to have the answer. In part, the comment says:
The reason why this adapter exists is because Lightning is simply not capable of streaming a “raw” HDMI signal across the cable. Lightning is a serial bus. There is no clever wire multiplexing involved. [...] Airplay uses a bunch of hardware h264 encoding technology that we’ve already got access to, so what happens here is that we use the same hardware to encode an output stream on the fly and fire it down the Lightning cable straight into the ARM SoC the guys at Panic discovered. Airplay itself (the network protocol) is NOT involved in this process. The encoded data is transferred as packetized data across the Lightning bus, where it is decoded by the ARM SoC and pushed out over HDMI.
If the comment is legitimate -- and there's no way to know at this point if it is or not -- Apple is basically hanging all the electronics outside the device, rather than glutting Lightning up with signals that may fall into disuse over the time. There are trade-offs, to be sure, but given how the old 30-pin Dock connector abandoned FireWire over time, added HDMI, and jumbled in everything from line to serial, if accurate, this could also be a better, more future-proof solution.
And, since the on-device side is software-centric, an update could improve the HDMI out to true 1080p. Fingers crossed.
If anyone has any specific knowledge of how this kind of stuff works, give the full comment a read via the link below and then please weigh in a let me know how likely (or unlikely) it all sounds.
Source: Panic Blog comment