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The Lightning Digital AV Adapter Surprise

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Re: The Lightning Digital AV Adapter Surprise

#11

Post by cabel »

drivebyacct2 wrote: post #7
tptacek wrote: post #6

Earlier quoted context omitted.

You think Cabel Sasser doesn't know what Airplay is?

I honestly don't know. Someone is somehow implying that the adapter is implementing a full stack capable of being an AirPlay receiver and transcoding video on the fly. I think Cabel is wrong or has explained what they think is occuring incorrectly. /shrug

In this case, AirPlay is our easier-to-understand way of saying "the results you're getting are exactly the same as when you stream iOS video using AirPlay". (Which is really weird for a video-out dongle! Especially since the former, non-Lightning one did proper video out.)

I've tweaked the post to make it clearer that AirPlay isn't _necessarily_ the _exact_ mechanism being used! It could just be H.264 or MPEG or whatever.

Mostly I'd love to know exactly what this chip/system does, so if anyone here with far more advanced hardware knowledge than any of us have feels up to hacking around, that'd be amazing! :)

The key takeaways from the post are:

1. It's feels unusual that a AV adapter would have a full SoC ARM-based CPU with RAM etc, not just a video encoder/decoder chip. Is it unusual? Let me know. :)

2. It's a bummer that the Video Out isn't very good, and not true 1080p, and has MPEG artifacts.

(Thanks for sharing the link.)

Re: The Lightning Digital AV Adapter Surprise

#13

Post by drivebyacct2 »

cabel wrote: post #11
drivebyacct2 wrote: post #7

Earlier quoted context omitted.

I honestly don't know. Someone is somehow implying that the adapter is implementing a full stack capable of being an AirPlay receiver and transcoding video on the fly. I think Cabel is wrong or has explained what they think is occuring incorrectly. /shrug

In this case, AirPlay is our easier-to-understand way of saying "the results you're getting are exactly the same as when you stream iOS video using AirPlay". (Which is really weird for a video-out dongle! Especially since the former, non-Lightning one did proper video out.) I've tweaked the post to make it clearer that AirPlay isn't _necessarily_ the _exact_ mechanism being used! It could just be H.264 or MPEG or wha…

Yeah, someone mentioned something similar elsewhere in the thread and it certainly makes sense to me. It fits in with the comparison to Miracast, the need for hardware support for full screen mirroring over AirPlay. I can see the adapter processing a stream in a similar format or some such as AirPlay (without being a classic "AirPlay receiver" which is what I was hung up on)

For your two points:

1. I think that comes with the territory of being a Lightnin accessory and makes sense if they're doing some sort of compression or something before hand. It certainly fits with Apple's persona. Control the content, don't let any-old-body create a video adapter. They have to deal with Apple's handshake/stream/whatever because Apple doesn't pin-out the HDMI for the Lightning connector...

2. That is a major bummer and seems like one of those "details" that Apple would get right. I'm certainly curious the more I think about it as well.

Re: The Lightning Digital AV Adapter Surprise

#14

Post by userna »

supercoder wrote: post #4

I think they're way off on the theory the cable is running iOS. I think what's most likely is the phone is putting out a h264 stream and the chip is just decoding it. Rather than a whole ios stack & AirPlay protocol. Sure this shares some similarities with how AirPlay works (showing a h264 stream from the device ) but wouldn't require a whole system on a chip just for showing this feed.

Actually, they're dead on. (And no, I won't corroborate that further. But it does download a stub copy of iOS.)

Re: The Lightning Digital AV Adapter Surprise

#15

Post by pifflesnort »

userna wrote: post #14
supercoder wrote: post #4

I think they're way off on the theory the cable is running iOS. I think what's most likely is the phone is putting out a h264 stream and the chip is just decoding it. Rather than a whole ios stack & AirPlay protocol. Sure this shares some similarities with how AirPlay works (showing a h264 stream from the device ) but wouldn't require a whole system on a chip just for showing this feed.

Actually, they're dead on. (And no, I won't corroborate that further. But it does download a stub copy of iOS.)

This provides no useful information whatsoever. I wouldn't be hugely surprised if they wrote code to the ARM MCU (if it has 2GB of RAM to work with), but what does "stub copy of iOS" even mean?

Also. Jimmy Hoffa is buried inside that microcontroller. I won't corroborate this further, but this is the dead-on truth.

Re: The Lightning Digital AV Adapter Surprise

#16

Post by wmf »

zacharyvoase wrote: post #2

Most cables that adapt signals from one format to another are 'active' (that is, contain a microcontroller). c.f.: https://en.wikipedia.org/wiki/Active_cable

But there's a big difference between demuxing (e.g. DisplayPort to HDMI) and decompressing video.

Re: The Lightning Digital AV Adapter Surprise

#18

Post by mortenlarsen »

pifflesnort wrote: post #15
userna wrote: post #14

Earlier quoted context omitted.

Actually, they're dead on. (And no, I won't corroborate that further. But it does download a stub copy of iOS.)

This provides no useful information whatsoever. I wouldn't be hugely surprised if they wrote code to the ARM MCU (if it has 2GB of RAM to work with), but what does "stub copy of iOS" even mean? Also. Jimmy Hoffa is buried inside that microcontroller. I won't corroborate this further, but this is the dead-on truth.

2Gb = 2 GigaBit = 256MB RAM. It is common to measure individual RAM chips in bits, not bytes.

Re: The Lightning Digital AV Adapter Surprise

#20

Post by shabble »

If bored, you could try probing those various little gold test pads on the off chance they have a debug port[1] somewhere. Then again, Apple paranoia makes that overwhelmingly unlikely.

[1] http://www.devttys0.com/2012/11/reverse-engineering-serial-p... (although JTAG is probably much more likely if anything)

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