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Comment by stefan_ | Hacker News Reader

The VideoCore 4 (fuck the roman numerals, for exactly this reason) can not output 4k and it is also not a ES 3.0 capable GPU. So this must be a 5 or 6.

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I'm crossing my fingers here. This is really something they should have put in the specs if it's supported. With 10bit decoding and Rec. 2100 [1] support, this would make a fantastic platform to build a media center on. I'd certainly upgrade from the Pi 3 even though I don't currently have a 4K television.

[1] https://en.wikipedia.org/wiki/Rec._2100

I looked at the dmesg from someones Phoronix testsuite run and it has:

[drm] Initialized v3d 1.0.0 20180419 for fec00000.v3d on minor 0

So this is vc5/6, not vc4. Additionally:

    Vendor: Broadcom (0x14e4)
    Device: V3D 4.2 (0xffffffff)

Do we know for sure that all VC5/6 SoCs support HDR decoding, or is that still unknown? The Wikipedia page for VideoCore only lists one VC5 SoC and no VC6 SoCs. The Broadcom page for the VC5 SoC is pretty uninformative.

Edit: I found this thing someone on the RaspPi forums put together! https://cdn.shopify.com/s/files/1/1560/1473/files/Inside_Ras...

> The Pi 4 has seen an upgrade to VideoCore VI.

> The H.265 / HEVC decoder is a HEVCv2 Main 4:4:4 10 design supporting bitstreams up to profile 5.1

Sounds promising! (The documentation on the website should certainly be fixed if this is correct.) Now assuming Rec. 2100 is properly supported to allow connecting to HDR capable displays over HDMI 2.0, we should be good!

The KMS in this new chip is still the old VC4 HVS (high-speed video scaler). That chip can not output any 10 bit formats.

(But it also wasn't capable of 4k60, so maybe there are some modifications there.)

This was mentioned in the rpi forum by staff:

    May I ask whether RPI supports things such as 10 bit video decoding, Dolby Vision and Atmos? Thx.

HEVC hardware decode supports 4kp60, 10-bit. Audio output is pretty much unchanged, but the HDMI audio channels now support 8x192kHz bitrates.

Sure, but the video decode IP is a different piece of hardware from the video scaler/compositor. In a typical SoC, you have the GPU and the video decode engines as separate blocks that feed into the video scaler/compositor which then blends, rotates, scales, .. etc the inputs and feeds the final signal to LVDS, HDMI or whatever.

Now does it make sense to have your video decoder support 10 bit when your compositor can't handle that format? I guess you could argue that 10 bit source material will still improve the quality even if you downsample it to 8 bit for display, and I think for example DVB-T2 has standardized on 10 bit so if you can't decode that, that's a large chunk of market gone.

Ultimately, from the little we know, the compositor hardware is the same as the old Rpi, and that couldn't do 4k60 and it can't do 10 bit depths. The Raspbian image currently doesn't use the Linux kernel implementation for driving the compositor (it uses the fkms or "firmware kernel mode setting") so there might well have been hardware tweaks.

(Ok, instead of making this comment thread any longer, I simply asked and the compositor hardware in the RPi indeed has HDR support:

https://github.com/raspberrypi/linux/issues/3020#issuecommen...

Tweaked from the old HVS in the old RPis.)

Yeah, that makes sense - you wouldn't want to gimp the system by only doing half a job :)

> Sounds promising! (The documentation on the website should certainly be fixed if this is correct.) Now assuming Rec. 2100 is properly supported to allow connecting to HDR capable displays over HDMI 2.0, we should be good!

As hopeful as I am, that's quite a big assumption...

What are the odds that this will support 1080p streaming with Plex? I've tried Plex on a Pi 3 using a Roku as a player with 1080p and it's a complete failure. Plex tries to encode everything even if native playback to the Roku is possible using the Roku media player.

If encoding is required? Almost certainly won't work, it's just not powerful enough. But you should avoid reencoding if at all possible, and I imagine it will work if you can manage to disable it.

My plex isn't on a Pi but I do not have this issue with Roku Express as a player. Could be other factors like the video codec and direct stream is set on Roku.

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