fix(macos): capture and tag the screen track as BT.709 studio range

electron/native/screencapturekit/Sources/OpenScreenCaptureCore/VideoColor.swift

@@ -0,0 +1,22 @@
+import AVFoundation
+import CoreGraphics
+
+// The colour every recording is decoded as: BT.709 primaries, transfer and matrix, studio
+// range. The compositor assumes it for every file, and the Windows (#929) and Linux (#932)
+// helpers write it. Left to the defaults, ScreenCaptureKit hands over the display's own colour
+// space (P3 on most Macs) and VideoToolbox picks the matrix and the tags
+// (getopenscreen/openscreen#943).
+//
+// Range has no key here: it comes from the pixel format, and the stream captures `420v`, the
+// studio-range one.
+
+/// The matrix ScreenCaptureKit converts to YCbCr with. It has to be the one the file is tagged
+/// with in `videoColorProperties`, which `VideoColorTests` pins.
+public let captureYCbCrMatrix: CFString = CGDisplayStream.yCbCrMatrix_ITU_R_709_2
+
+/// `AVVideoColorPropertiesKey` for the H.264 writer input.
+public let videoColorProperties: [String: String] = [
+	AVVideoColorPrimariesKey: AVVideoColorPrimaries_ITU_R_709_2,
+	AVVideoTransferFunctionKey: AVVideoTransferFunction_ITU_R_709_2,
+	AVVideoYCbCrMatrixKey: AVVideoYCbCrMatrix_ITU_R_709_2,
+]

electron/native/screencapturekit/Sources/OpenScreenScreenCaptureKitHelper/ScreenCaptureRecorder.swift

@@ -701,7 +701,15 @@ final class ScreenCaptureRecorder: NSObject, SCStreamOutput, SCStreamDelegate {
 		configuration.minimumFrameInterval = CMTime(value: 1, timescale: CMTimeScale(max(1, request.video.fps)))
 		configuration.queueDepth = 6
 		configuration.showsCursor = !request.video.hideSystemCursor
-		configuration.pixelFormat = kCVPixelFormatType_32BGRA
+		// Studio-range BT.709 YCbCr from ScreenCaptureKit itself, which the encoder takes as is
+		// and the compositor decodes (#943). BGRA left the matrix to VideoToolbox. Nothing here
+		// reads the pixels: a frame goes through `retimedSampleBuffer` (timing only) to
+		// `append`, and `isCompleteFrame` reads attachments. 1.5 bytes a pixel instead of 4,
+		// times `queueDepth`.
+		configuration.pixelFormat = kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange
+		configuration.colorMatrix = captureYCbCrMatrix
+		// Unset, the buffers carry the display's colour space: P3 on most Macs.
+		configuration.colorSpaceName = CGColorSpace.sRGB
 		configuration.sampleRate = 48_000
 		configuration.channelCount = 2
 		configuration.excludesCurrentProcessAudio = true
@@ -754,6 +762,8 @@ final class ScreenCaptureRecorder: NSObject, SCStreamOutput, SCStreamDelegate {
 			AVVideoCodecKey: AVVideoCodecType.h264,
 			AVVideoWidthKey: outputWidth,
 			AVVideoHeightKey: outputHeight,
+			// BT.709 tags, the colour the stream is captured in (#943).
+			AVVideoColorPropertiesKey: videoColorProperties,
 			AVVideoCompressionPropertiesKey: [
 				// From the size this stream really got. The renderer sends none (#924).
 				AVVideoAverageBitRateKey: request.video.bitrate

electron/native/screencapturekit/Tests/OpenScreenCaptureCoreTests/VideoColorTests.swift

@@ -0,0 +1,18 @@
+import AVFoundation
+import XCTest
+
+import OpenScreenCaptureCore
+
+/// The file has to say what its samples are: a matrix that converts with one standard and tags
+/// another is the shifted-hue defect #943 exists to remove.
+final class VideoColorTests: XCTestCase {
+	func testCaptureMatrixIsTheOneTheFileIsTaggedWith() {
+		XCTAssertEqual(captureYCbCrMatrix as String, videoColorProperties[AVVideoYCbCrMatrixKey])
+	}
+
+	func testFileIsTaggedBT709() {
+		XCTAssertEqual(videoColorProperties[AVVideoColorPrimariesKey], "ITU_R_709_2")
+		XCTAssertEqual(videoColorProperties[AVVideoTransferFunctionKey], "ITU_R_709_2")
+		XCTAssertEqual(videoColorProperties[AVVideoYCbCrMatrixKey], "ITU_R_709_2")
+	}
+}