From fd39084e8885ca26db9cbc6ba10756d0e6062c5b Mon Sep 17 00:00:00 2001
From: Vanilagy <1696106+Vanilagy@users.noreply.github.com>
Date: Thu, 19 Mar 2026 15:08:29 +0100
Subject: [PATCH] Simplify/fix 3d matrix rotation extraction (#330)

---
 src/isobmff/isobmff-demuxer.ts | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/src/isobmff/isobmff-demuxer.ts b/src/isobmff/isobmff-demuxer.ts
index d52e160..02be3fb 100644
--- a/src/isobmff/isobmff-demuxer.ts
+++ b/src/isobmff/isobmff-demuxer.ts
@@ -3177,22 +3177,16 @@ const offsetFragmentTrackDataByTimestamp = (trackData: FragmentTrackData, timest
 
 /** Extracts the rotation component from a transformation matrix, in degrees. */
 const extractRotationFromMatrix = (matrix: TransformationMatrix) => {
-	const [m11, , , m21] = matrix;
+	const [a, b] = matrix; // (1, 0) projects onto (a, b), so that's all we need
 
-	const scaleX = Math.hypot(m11, m21);
+	const radians = Math.atan2(b, a);
 
-	const cosTheta = m11 / scaleX;
-	const sinTheta = m21 / scaleX;
-
-	// Invert the rotation because matrices are post-multiplied in ISOBMFF
-	const result = -Math.atan2(sinTheta, cosTheta) * (180 / Math.PI);
-
-	if (!Number.isFinite(result)) {
+	if (!Number.isFinite(radians)) {
 		// Can happen if the entire matrix is 0, for example
 		return 0;
 	}
 
-	return result;
+	return radians * (180 / Math.PI);
 };
 
 const sampleTableIsEmpty = (sampleTable: SampleTable) => {