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White Clipping

tvOS Video playback support subforum
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barong
Posts: 58
Joined: 07 Nov 2017, 07:33

White Clipping

Post by barong » 17 Dec 2017, 15:53

I have noticed MrMC is clipping whites in SDR playback.
Using this file:
https://m.youtube.com/watch?v=3vCn5JXny8w

Values over 234 are clipped. Playing this back in the inbuilt YouTube app works fine with no clipping.

I notice that there is a setting under acceleration that stops it from clipping, but it also elevates the black level to full range/0 instead of video black /16.

Wondering if there can be another option that leaves video black at 16 but doesn’t clip whites eg. 16 - 253?

Hope this makes sense.

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davilla
Team MrMC
Posts: 3656
Joined: 26 Oct 2015, 17:01

Re: White Clipping

Post by davilla » 17 Dec 2017, 17:00

The choice is limited (16 - 234) or full (0 - 255). There is no video spec for 16 - 253.

You can always adjust brightness/contract for ffmpeg/videotoolbox but not avfoundation codecs.

cosmoxl
Posts: 1407
Joined: 12 Dec 2015, 14:16

Re: White Clipping

Post by cosmoxl » 17 Dec 2017, 17:12

davilla wrote:
17 Dec 2017, 17:00
The choice is limited (16 - 234) or full (0 - 255). There is no video spec for 16 - 253.

You can always adjust brightness/contract for ffmpeg/videotoolbox but not avfoundation codecs.
16-253 is actually what I get with the ATV4 using AVF, or other "native players", and with roku devices, and what I used to get with shield TV, all using ycbcr 444 8bit.

barong
Posts: 58
Joined: 07 Nov 2017, 07:33

Re: White Clipping

Post by barong » 17 Dec 2017, 23:39

davilla wrote:
17 Dec 2017, 17:00
The choice is limited (16 - 234) or full (0 - 255). There is no video spec for 16 - 253.

You can always adjust brightness/contract for ffmpeg/videotoolbox but not avfoundation codecs.
That may be the case, but just about all other media players operate this way with black level 16 and not clipping whites.
Youtube, TV's inbuilt player (various manufacturers), various kodi boxes etc.

I understand if it is a limitation of the Apple TV 4K though and it can't be implemented.

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davilla
Team MrMC
Posts: 3656
Joined: 26 Oct 2015, 17:01

Re: White Clipping

Post by davilla » 18 Dec 2017, 01:31

They might operate this way but the actual video content comes in two forms for SDR. Limited or Full. There is nothing in between.

If you want to 'boost' the white levels, use the contrast setting in the video OSD. A value of 43-45 should create the desired effect.

Note, All XBMC/Kodi/SPMC/MrMC share the identical code for color range scaling. They all treat limited as 16-235. That is the spec definition of limited range for video content.

barong
Posts: 58
Joined: 07 Nov 2017, 07:33

Re: White Clipping

Post by barong » 29 Oct 2018, 03:31

Just a followup on this (very old) post...
I have worked out that enabling Hardware Acceleration - VideoToolbox is causing this for my setup.
Disabling it gives me the expected results.

I also tested the colour space with and without it enabled using this pattern:
http://spearsandmunsil.com/portfolio-it ... r-space-2/

When HWA is enabled, the colours are clipped and the Colour Space and Chrome Range is not converted properly.
When disabled (so decoded via SW), everything displays as it should.

Again, this could be something to do with my display, but as the Apple TV 4K has plenty of CPU grunt I think I'll leave HWA disabled for now.

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