Auto-switch macOS HDR when IINA plays an HDR video

[dylanbuchi]

Hi! I made a small free tool for IINA users with an HDR external monitor. It reads video-params through mpv's IPC socket. When the gamma is PQ/HLG or the video is Dolby Vision, it turns macOS HDR on (and brightness up), and puts both back when playback stops.

It adds one option in Advanced settings: input-ipc-server=/tmp/mpvsocket. Nothing else in IINA changes.

https://github.com/dylanbuchi/iina-auto-hdr

Tested on macOS 27.0.1 with IINA 1.5.0. Happy to hear if it works on other setups.

[low-batt]

Hello from a junior IINA developer,

I do not see a discussion of why this is needed. IINA itself does this. Or at least tries to. Is this needed because macOS fails to properly support non-Apple external HDR displays?

To determine if a display is capable of supporting HDR, IINA checks the value of the property NSScreen.maximumPotentialExtendedDynamicRangeColorComponentValue:

The value of this property is determined when you create the NSScreen object, and doesn’t change afterwards. If this property is greater than 1.0, the screen supports EDR values. If the screen doesn’t support EDR values, the value is 1.0.

Is macOS returning a value that indicates the display is not capable of HDR when it is?

What macOS is telling IINA can be seen in messages near the start of the log file:

09:16:06.223 [iina][d] Display 2 (main, online):
  Product name: LG UltraFine
  Model: 23412
  Vendor: 40557
  Bounds: (0.0, 0.0, 2560.0, 1440.0)
  Mode: 2560x1440 @ 60 Hz
  Native modes:
    5120x2880 @ 60 Hz
09:16:06.223 [iina][d] NSScreen.screens[0], LG UltraFine (main screen), on display 2:
  Frame: (0.0, 0.0, 2560.0, 1440.0), visible (0.0, 62.0, 2560.0, 1348.0)
  EDR: Not supported, max potential 1.0, max current 1.0

That is my external Apple / LG UltraFine display which does not support HDR.

The status of EDR support is also reported when IINA starts playing a HDR video:

09:18:31.337 [hdr0][d] Refreshing HDR for player0 on display2, LG UltraFine:
  EDR: Not supported, max potential 1.0, max current 1.0
09:18:31.337 [hdr0][d] Video gamma=pq, primaries=bt.2020, sig_peak=4.926108360290527
09:18:31.337 [hdr0][d] HDR video was found but the display does not support EDR mode

What is happening with your display?

[dylanbuchi]

Thanks for looking into this! Yes, that's exactly it. On my external HDR monitor (Acer Predator X32 FP), macOS reports EDR as not supported while the system "High Dynamic Range" switch in Display settings is off, which is how most people keep it because the desktop looks washed out with HDR on. From my IINA log:

00:56:56 [hdr0] EDR: Not supported, max potential 1.0, max current 1.0
00:56:56 [hdr0] HDR video was found but the display does not support EDR mode

iina-auto-hdr flips that system switch when an HDR video starts. A few seconds later IINA refreshes on its own and picks it up:

00:57:02 [hdr0] EDR: Supported, max potential 12.337686538696289, max current 1.0
00:57:02 [hdr0] Using HDR color space instead of ICC profile

So it doesn't replace IINA's HDR handling, it just turns on the macOS switch IINA needs, and turns it off when playback stops. Built-in Apple XDR displays don't need it, since their HDR is always available.

If IINA ever wanted to do this natively, I'd be happy to help, though the switch is a private SkyLight API (SLSDisplaySetHDRModeEnabled), so it may not be something you'd want in IINA itself.

[low-batt]

Thank you very much for explaining. Sounds like on the external display macOS is unable to control HDR on an individual window basis. Does the display not have localized dimming, or is this just poor support by macOS?

On IINA doing this natively…

Using a private API does not rule that out. Not sure how the senior developers will feel about adding use of another private API, but IINA's PiP feature uses private APIs, so there is precedent to point to.

At the moment IINA needs to focus on fixing a number of problems. The highest priority is adding support for GPU Next and Metal. GPU Next fixes a lot of HDR problems.

[dylanbuchi]

Thanks! It's not about local dimming. On an external HDR10 monitor, HDR is a signal mode for the whole display: macOS has to switch the output to an HDR (PQ) signal, and that's all or nothing. macOS only does it when the "High Dynamic Range" toggle in Display settings is on, never automatically when an app requests EDR. Apple's XDR displays are different because the Mac drives the backlight itself, so EDR can work per window there.

Makes total sense to focus on GPU Next first. If native support ever comes up, I'm happy to help or share what I found about the private call. Until then the tool covers it.