Comment by dwaite

> yes I know there was one iPad that could do USB 3 with one special dongle - and it couldn’t even do video out well with the dongle. The video adapter had hardware to decompress a compressed video stream and convert it.

Those are two separate things.

These iPad models had USB 3.0 over lightning. Lighting however was designed to solve the 30 pin connector "alt mode" problem. USB-C recreated the "alt mode" problem.

In the original 30-pin iPod, iPhone and iPad days, you had multiple video out adapters to support RCA, VGA, composite, and so on. These were also _different_ with the different i-device models - the adapters were not backward compatible, so when they came out with a new higher-resolution model of dongle, it wouldn't work on older devices. Conversely, the complexity of supporting various hardware mappings onto the 30 pin connector meant that older dongles could get deprecated from new devices.

There weren't a lot of people who invested in video output for their I-devices, but for those who did this was a very frustrating issue.

So for lightning, they went to serial protocols. So rather than negotiate a hardware mode where certain pins acted like HDMI pins in a pass-through mode, they streamed a H.264 video to the dongle - the dongle then rendered it and used its own HDMI output support.

Since this was software negotiation, a newer dongle could support new video formats and higher resolutions while still supporting older devices. There were also examples of improvements pushed to more complicated dongles like the HDMI adapter via software updates. But fundamentally, the complexity of supporting a broad hardware accessory ecosystem wasn't pushed into the physical port - it could evolve over time via more complex software rather than via increasingly complicated hardware in every phone.

With USB-C we are back to guessing whether the connector is expecting the phone to support HDMI alt mode, DisplayPort alt mode, MHL alt mode, or to output a proprietary system like DisplayLink data.

USB 3.0 (which is what these iPads supported) never had these alt modes. It was USB-C which became a connector for (optionally) supporting a lot of other, non-USB protocols. The lack of USB-C support is why these iPads only supported video out with the lightning to HDMI adapter.

USB-C is decent, but it suffers quite a bit from there not being strong certification. This is partly why Thunderbolt 5 has shifted to becoming a compatibility- and capability- oriented certification mark. You know for example that thunderbolt 5 video will always work, because the cables have all the data pins and the devices are going to support DisplayPort alt mode.