When i use AVPlayer to obtain the video frame CVPixelBufferRef of an HDR video, and use AVSampleBufferDisplayLayer to display it on the screen, after a period of time, the HDR video content and screen gradually darken, losing the HDR effect. Steps to reproduce: Create an AVPlayer to loop an HDR video, specify the video frame format as kCVPixelFormatType_420YpCbCr10BiPlanarVideoRange Create a timer to get the video frame CVPixelBufferRef at 30 frames per second Use AVSampleBufferDisplayLayer to display CVPixelBufferRef on the screen Don't operate the phone, wait for a period of time (such as 40 minutes), the HDR effect disappears and the screen darkens Note: You need to use an iPhone device, iOS 18.5 and below operating system You need to ensure that the HDR video is played in a loop, that is, to ensure that the screen continues to display HDR content, wait for a period of time, depending on different devices, you need to wait for 20-40 minutes. In the iPhone Photos app,the same problem will occur after playing HDR video in a loop for a long time Expected Results: When rendering HDR content for a long time, it is guaranteed that there is always an HDR effect, and the HDR content and screen will not be darkened. Current Results: After about 20-40 minutes, the HDR effect disappears and the screen darkens.

When I play an HDR video in the iPhone Photos app, I can see the HDR effect obviously. But if this HDR video is played continuously for more than 30-40 minutes, the HDR effect will disappear and the brightness will be compressed to the SDR range. This issue will appear on any iPhone. Depending on the phone, it may be 20-30 minutes, or 30-40 minutes, or even a few minutes, such as iPhone 12 mini. Similarly, if I use AVPlayer to play and preview an HDR video, if it plays more than 30-40 minutes, the HDR effect will disappear and the screen brightness will dim. Also the currentEDRHeadroom will gradually decrease to 1 Note, test it with an HDR video longer than 1 hour, and if the video is short, please loop it. My question is how to avoid losing the HDR effect after 30-40 minutes when I use CAMetalLayer to render any HDR video.

On an iOS 18 phone, I use AVCaptureSession to capture HDR with x420 format. The output CMSampleBuffer is HLG colorspace, the propagated attachments contain kCVImageBufferAmbientViewingEnvironmentKey and kCVImageBufferSceneIlluminationKey. Now I use CAMetalLayer to render the CVPixelBuffer to the screen, but the brightness is brighter than AVSampleBufferDisplayLayer. Here is my code. - (void)_updateColorSpaceIfNeed:(CVPixelBufferRef)pixelBuffer { CAMetalLayer *layer = (CAMetalLayer *)_mtkView.layer; if (![layer isKindOfClass:CAMetalLayer.class]) return; layer.wantsExtendedDynamicRangeContent = YES; CFDataRef ambientViewingEnvironment = (CFDataRef)CVBufferCopyAttachment(pixelBuffer, kCVImageBufferAmbientViewingEnvironmentKey, NULL); NSData *data = (__bridge NSData *)ambientViewingEnvironment; if (ambientViewingEnvironment) CFRelease(ambientViewingEnvironment); CAEDRMetadata *metadata = [CAEDRMetadata HLGMetadataWithAmbientViewingEnvironment:data]; // CAEDRMetadata *metadata = [CAEDRMetadata HLGMetadata]; layer.EDRMetadata = metadata; layer.pixelFormat = MTLPixelFormatRGBA16Float; CGColorSpaceRef colorspace = CGColorSpaceCreateWithName(kCGColorSpaceITUR_2100_HLG); layer.colorspace = colorspace; if (colorspace) CGColorSpaceRelease(colorspace); } Why does the CAEDRMetadata class have "HLGMetadataWithAmbientViewingEnvironment:" and "HLGMetadata" methods, but does not provide the "HLGMetadataWithAmbientViewingEnvironment:sceneIllumination" method? I want to know how kCVImageBufferAmbientViewingEnvironmentKey and kCVImageBufferSceneIlluminationKey affect tone mapping. Is there any documentation I can refer to?