Clicking the "Limit to SDR" and "Allow Full HDR (as supported)" should show a significant difference if you device supports HDR. If you don't see a difference then your device doesn't support HDR (or your browser)
For these images, there's a specific extension to JPEG where they store the original JPEG like you've always seen, and then a separate embedded gain map to add brightness if the device supports it. That's for stills (JPEGs) though, not video but the "on the wire difference" is that gain map
I'm not an expert but for videos, ATM, afaict, they switched them to 10bits (SDR is 8bits), and added metadata to map that 10 bits to values > "white" where white = 100nits. This metadata (PQ or HLG) can map those 10 bits up to 10000 nits.
If so, try this: https://gregbenzphotography.com/hdr-gain-map-gallery/
Clicking the "Limit to SDR" and "Allow Full HDR (as supported)" should show a significant difference if you device supports HDR. If you don't see a difference then your device doesn't support HDR (or your browser)
For these images, there's a specific extension to JPEG where they store the original JPEG like you've always seen, and then a separate embedded gain map to add brightness if the device supports it. That's for stills (JPEGs) though, not video but the "on the wire difference" is that gain map
I'm not an expert but for videos, ATM, afaict, they switched them to 10bits (SDR is 8bits), and added metadata to map that 10 bits to values > "white" where white = 100nits. This metadata (PQ or HLG) can map those 10 bits up to 10000 nits.