3 ms·

While I can see the technical reason why channel changes take a while with digital TV, I've always wondered why switching the digital input of your TV, or just

While I can see the technical reason why channel changes take a while with digital TV, I've always wondered why switching the digital input of your TV, or just changing the resolution of the connected devices takes so long. On most TVs it's over two seconds. The signal is in most cases just a stream of standalone, uncompressed frames. Switching from HDMI1 to HDMI2 should take a few milliseconds.

gregmac 6y ago
There's a lot going on: HDCP handshake, resolution negotiation, HDMI-CEC setup.. HDCP obviously being consumer-hostile, but the others are decent features to make things "just work".
- iforgotpassword 6y ago
  Ok so HDCP might be an explanation although I wonder if it has any impact if it's not in use. Don't really know how it works tbh. As for the rest: Resolution negotiation is optional and wouldn't matter if the device is already outputting at some resolution, also this happens on different pins, so even if the device would first query the EDID of the TV to figure out what mode it prefers, the TV could meanwhile already display whatever the device is outputting. Same with CEC, this is another protocol on different pins than where the picture data is sent. HDMI really is just DVI with some extras, at least for the older versions.
- Dylan16807 6y ago
  Why didn't it already do all of that, before I told it to switch inputs?
formerly_proven 6y ago
I don't know why (but would be interested), but even PC screens are usually very slow at switching (>1 second delay), and for some inexplicable reason practically all of them turn their backlight off while doing it.
kergonath 6y ago
I’ve always assumed that’s because TV manufacturers choose the most under-powered SoC they can get away with, don’t put half as much RAM as it needs, and let loose incompetent programmers who don’t have to use the damn thing ever. Still very frustrating.

gregmac 6y ago

There's a lot going on: HDCP handshake, resolution negotiation, HDMI-CEC setup.. HDCP obviously being consumer-hostile, but the others are decent features to make things "just work".

iforgotpassword 6y ago
Ok so HDCP might be an explanation although I wonder if it has any impact if it's not in use. Don't really know how it works tbh. As for the rest: Resolution negotiation is optional and wouldn't matter if the device is already outputting at some resolution, also this happens on different pins, so even if the device would first query the EDID of the TV to figure out what mode it prefers, the TV could meanwhile already display whatever the device is outputting. Same with CEC, this is another protocol on different pins than where the picture data is sent. HDMI really is just DVI with some extras, at least for the older versions.
Dylan16807 6y ago
Why didn't it already do all of that, before I told it to switch inputs?

formerly_proven 6y ago

I don't know why (but would be interested), but even PC screens are usually very slow at switching (>1 second delay), and for some inexplicable reason practically all of them turn their backlight off while doing it.

kergonath 6y ago

I’ve always assumed that’s because TV manufacturers choose the most under-powered SoC they can get away with, don’t put half as much RAM as it needs, and let loose incompetent programmers who don’t have to use the damn thing ever. Still very frustrating.