gtechn
Posts: 161
Joined: Thu Jan 07, 2016 5:32 pm

4K decode limitations?

Wed Jun 26, 2019 1:45 am

Hello! Congrats on the RPi 4 release! Looks great, and it is beyond my best expectations for the new generation (and the 9-months-early announcement is delightful!)

I was looking at the specs, and it can power 1x4K monitor @ 60hz or 2x4K monitors @ 30hz. I also noticed the (amazing) ability to decode 4K H.265 @ 60fps. With this decode ability, what are the limitations? Is the H.265 decode limited to 1 4K display at a time, or can you H.265 decode on both 4K displays at the same time (albeit at 30fps)?

(Also, quick minor question not worth a second post: Was mini-HDMI too large? I'm just curious about the inconsistency with the Pi 4 and the Zero series.)

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 13235
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Location: ZZ9 Plural Z Alpha, aka just outside Cambridge.

Re: 4K decode limitations?

Wed Jun 26, 2019 7:25 am

Currently there is no arbitration between attempted uses of the hevc block, so trying to decode a 2nd stream will blow up. My understanding is that there is no reason why two streams can't be multiplexed through the block, but we need to get the software in place to do so.
It decodes to memory, and then the display pipeline reads back from memory, so you can put the output image wherever you like in the screen.

Mini hdmi connectors were still too big to get two into the space of one full sized one.
Software Engineer at Raspberry Pi Ltd. Views expressed are still personal views.
I'm not interested in doing contracts for bespoke functionality - please don't ask.

bunklung
Posts: 109
Joined: Tue Jun 25, 2019 12:10 pm

Re: 4K decode limitations?

Fri Jun 28, 2019 1:55 pm

6by9 wrote:
Wed Jun 26, 2019 7:25 am
Currently there is no arbitration between attempted uses of the hevc block, so trying to decode a 2nd stream will blow up. My understanding is that there is no reason why two streams can't be multiplexed through the block, but we need to get the software in place to do so.
It decodes to memory, and then the display pipeline reads back from memory, so you can put the output image wherever you like in the screen.

Mini hdmi connectors were still too big to get two into the space of one full sized one.
Is this limited to HEVC or all decoding including h.264?

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 31477
Joined: Sat Jul 30, 2011 7:41 pm

Re: 4K decode limitations?

Fri Jun 28, 2019 2:01 pm

bunklung wrote:
Fri Jun 28, 2019 1:55 pm
6by9 wrote:
Wed Jun 26, 2019 7:25 am
Currently there is no arbitration between attempted uses of the hevc block, so trying to decode a 2nd stream will blow up. My understanding is that there is no reason why two streams can't be multiplexed through the block, but we need to get the software in place to do so.
It decodes to memory, and then the display pipeline reads back from memory, so you can put the output image wherever you like in the screen.

Mini hdmi connectors were still too big to get two into the space of one full sized one.
Is this limited to HEVC or all decoding including h.264?
Just the HEVC, which is a completely new and different HW block to the H264 block, which is still the old block.
Principal Software Engineer at Raspberry Pi Ltd.
Working in the Applications Team.

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