It's compressed data via an H.264 stream. USB-C has way more bandwidth, especially once Gen2 comes out.
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Really? Other than Lightning, what non-standard interfaces have they adopted recently? If anything they're waaaaay better now and over the past 5 years than they've been at any other point.
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You're confusing compressed vs. uncompressed with frame size and frame rate. ATV and Lightning take compressed H.264 1080p and pass it out as uncompressed video, according to such analysis. It's still 1080p, just not uncompressed video like DisplayPort. Which is why USB-C is rocking for computers.