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The Lightning-to-HDMI adapter is also an insane miniaturization. It runs a (very) stripped down version of iOS/darwin (not sure what apple counts it as) that is

by trangus_1985 5y ago

The Lightning-to-HDMI adapter is also an insane miniaturization. It runs a (very) stripped down version of iOS/darwin (not sure what apple counts it as) that is loaded in about a second when you plug in the phone, establishes a network connection, and streams compressed video frames over the network over USB to the HDMI. That's why when you use the iPhone HDMI adapter, everything looks a little bit compressed. Because it is.

gregsadetsky 5y ago
I didn’t know about this! Thank you. Truly nuts: https://hackaday.com/2019/07/30/apple-lightning-video-adaptors-run-ios-dynamically-loaded/ https://hackaday.com/2019/07/30/apple-lightning-video-adapto...
crazygringo 5y ago
Yup. It's actually an incredibly clever piece of tech that lets the iPad/iPhone get around the fact that lightning doesn't have enough bandwidth to transmit HDMI. For regular home/app views, it does hardware compression of the iPad's screen, outputs that over lightning, then the adapter decompresses it to raw HDMI. While for Netflix/etc. streams, it outputs the stream directly to the adapter to decompress, without quality loss. (And at full size as well, rather than double-letterboxed.) I still haven't figured out the magic of how apps like Netflix are able to do overlays of subtitles on top of the compressed video stream. Best I can tell, there must be a separate API for that, that gets sent in parallel.
- Dylan16807 5y ago
  As far as working within the constraints of USB 2, it's a solid way to do things. And I'll even leave aside the issue of running a whole OS just to decode video. But this is dealing with 1080p output. That's not very intensive. A lightning port has two high speed data pairs. You don't even need USB 3 speeds to transmit HDMI over one of those data pairs, and then put in like a $2 redriver. If you set up double-sided output I think you could even have a passive lightning to HDMI adapter. But that's a side issue, my main point is the bandwidth available that makes these tradeoffs unnecessary.
  - crazygringo 5y ago
    I'm not sure what point you're trying to make? Basic 1080p is 3.96 Gbps. Lightning is 480 Mbps. The bandwidth isn't there according to how lightning was designed.
    - Dylan16807 5y ago
      > Basic 1080p is 3.96 Gbps. Yes. (Well technically you need 3.20 or 3.33 for 1080p60, and HDMI 1.0 supports 3.96) > Lightning is 480 Mbps. The bandwidth isn't there according to how lightning was designed. Not true. Lightning has two differential data pairs. The port can do much more than 480 Mbps. If your response to that is "oh, but it's only connected to pins that do 480", they would have to reconnect it to video pins anyway to do HDMI out. And nothing else in the lightning ecosystem would limit it, because this is a directly-attached adapter. Also some of the iPad Pros have actual usb 3 support on their lightning ports.
outworlder 5y ago
Ok, this is the most amazing tidbit I've learned in this site in months. Thanks for the comment. Had no idea. Mind blown.

gregsadetsky 5y ago

I didn’t know about this! Thank you. Truly nuts: https://hackaday.com/2019/07/30/apple-lightning-video-adaptors-run-ios-dynamically-loaded/ https://hackaday.com/2019/07/30/apple-lightning-video-adapto...

crazygringo 5y ago

Yup. It's actually an incredibly clever piece of tech that lets the iPad/iPhone get around the fact that lightning doesn't have enough bandwidth to transmit HDMI. For regular home/app views, it does hardware compression of the iPad's screen, outputs that over lightning, then the adapter decompresses it to raw HDMI. While for Netflix/etc. streams, it outputs the stream directly to the adapter to decompress, without quality loss. (And at full size as well, rather than double-letterboxed.) I still haven't figured out the magic of how apps like Netflix are able to do overlays of subtitles on top of the compressed video stream. Best I can tell, there must be a separate API for that, that gets sent in parallel.

Dylan16807 5y ago
As far as working within the constraints of USB 2, it's a solid way to do things. And I'll even leave aside the issue of running a whole OS just to decode video. But this is dealing with 1080p output. That's not very intensive. A lightning port has two high speed data pairs. You don't even need USB 3 speeds to transmit HDMI over one of those data pairs, and then put in like a $2 redriver. If you set up double-sided output I think you could even have a passive lightning to HDMI adapter. But that's a side issue, my main point is the bandwidth available that makes these tradeoffs unnecessary.
- crazygringo 5y ago
  I'm not sure what point you're trying to make? Basic 1080p is 3.96 Gbps. Lightning is 480 Mbps. The bandwidth isn't there according to how lightning was designed.
  - Dylan16807 5y ago
    > Basic 1080p is 3.96 Gbps. Yes. (Well technically you need 3.20 or 3.33 for 1080p60, and HDMI 1.0 supports 3.96) > Lightning is 480 Mbps. The bandwidth isn't there according to how lightning was designed. Not true. Lightning has two differential data pairs. The port can do much more than 480 Mbps. If your response to that is "oh, but it's only connected to pins that do 480", they would have to reconnect it to video pins anyway to do HDMI out. And nothing else in the lightning ecosystem would limit it, because this is a directly-attached adapter. Also some of the iPad Pros have actual usb 3 support on their lightning ports.

outworlder 5y ago

Ok, this is the most amazing tidbit I've learned in this site in months. Thanks for the comment. Had no idea. Mind blown.