From bc316b3dc855e93d4d11e2c0d73d70326c38b889 Mon Sep 17 00:00:00 2001
From: NoFear0411 <9083405+NoFear0411@users.noreply.github.com>
Date: Sun, 1 Mar 2026 00:00:05 +0400
Subject: [PATCH] Fix near-1:1 SAR values falsely flagged as anamorphic

Encoders sometimes produce sample aspect ratios like 3201:3200
(0.03% off square) for content that has effectively square pixels.
The exact string comparison against "1:1" marks these as anamorphic,
which triggers unnecessary transcoding on clients that require
non-anamorphic video.

Parse the SAR ratio numerically and treat values within 1% of 1:1
as square pixels. This threshold is well clear of the nearest real
anamorphic SAR (PAL 4:3 at 16:15 = 6.67% off).
---
 .../Probing/ProbeResultNormalizer.cs          | 28 ++++++++++++++++++-
 .../Probing/ProbeResultNormalizerTests.cs     | 18 ++++++++++++
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/MediaBrowser.MediaEncoding/Probing/ProbeResultNormalizer.cs b/MediaBrowser.MediaEncoding/Probing/ProbeResultNormalizer.cs
index dbe5322897..471df369ba 100644
--- a/MediaBrowser.MediaEncoding/Probing/ProbeResultNormalizer.cs
+++ b/MediaBrowser.MediaEncoding/Probing/ProbeResultNormalizer.cs
@@ -863,7 +863,7 @@ namespace MediaBrowser.MediaEncoding.Probing
                 {
                     stream.IsAnamorphic = false;
                 }
-                else if (string.Equals(streamInfo.SampleAspectRatio, "1:1", StringComparison.Ordinal))
+                else if (IsNearSquarePixelSar(streamInfo.SampleAspectRatio))
                 {
                     stream.IsAnamorphic = false;
                 }
@@ -1154,6 +1154,32 @@ namespace MediaBrowser.MediaEncoding.Probing
             return Math.Abs(d1 - d2) <= variance;
         }
 
+        /// <summary>
+        /// Determines whether a sample aspect ratio represents square (or near-square) pixels.
+        /// Some encoders produce SARs like 3201:3200 for content that is effectively 1:1,
+        /// which would be falsely classified as anamorphic by an exact string comparison.
+        /// A 1% tolerance safely covers encoder rounding artifacts while preserving detection
+        /// of genuine anamorphic content (closest standard is PAL 4:3 at 16:15 = 6.67% off).
+        /// </summary>
+        internal static bool IsNearSquarePixelSar(string sar)
+        {
+            if (string.IsNullOrEmpty(sar))
+            {
+                return false;
+            }
+
+            var parts = sar.Split(':');
+            if (parts.Length == 2
+                && double.TryParse(parts[0], CultureInfo.InvariantCulture, out var num)
+                && double.TryParse(parts[1], CultureInfo.InvariantCulture, out var den)
+                && den > 0)
+            {
+                return IsClose(num / den, 1.0, 0.01);
+            }
+
+            return string.Equals(sar, "1:1", StringComparison.Ordinal);
+        }
+
         /// <summary>
         /// Gets a frame rate from a string value in ffprobe output
         /// This could be a number or in the format of 2997/125.
diff --git a/tests/Jellyfin.MediaEncoding.Tests/Probing/ProbeResultNormalizerTests.cs b/tests/Jellyfin.MediaEncoding.Tests/Probing/ProbeResultNormalizerTests.cs
index 8a2f84734e..40f853699b 100644
--- a/tests/Jellyfin.MediaEncoding.Tests/Probing/ProbeResultNormalizerTests.cs
+++ b/tests/Jellyfin.MediaEncoding.Tests/Probing/ProbeResultNormalizerTests.cs
@@ -39,6 +39,23 @@ namespace Jellyfin.MediaEncoding.Tests.Probing
         public void GetFrameRate_Success(string value, float? expected)
             => Assert.Equal(expected, ProbeResultNormalizer.GetFrameRate(value));
 
+        [Theory]
+        [InlineData("1:1", true)]           // exact square pixels
+        [InlineData("3201:3200", true)]     // 0.03% off — encoder rounding artifact (4K HEVC)
+        [InlineData("1215:1216", true)]     // 0.08% off — encoder rounding artifact
+        [InlineData("1001:1000", true)]     // 0.1% off — encoder rounding artifact
+        [InlineData("16:15", false)]        // 6.67% off — PAL DVD 4:3, genuinely anamorphic
+        [InlineData("8:9", false)]          // 11.1% off — NTSC DVD 4:3
+        [InlineData("32:27", false)]        // 18.5% off — NTSC DVD 16:9
+        [InlineData("10:11", false)]        // 9.1% off — DV NTSC
+        [InlineData("64:45", false)]        // 42.2% off — PAL DVD 16:9
+        [InlineData("4:3", false)]          // 33.3% off — classic anamorphic
+        [InlineData("0:1", false)]          // invalid/unknown SAR
+        [InlineData("", false)]             // empty
+        [InlineData(null, false)]           // null
+        public void IsNearSquarePixelSar_DetectsCorrectly(string sar, bool expected)
+            => Assert.Equal(expected, ProbeResultNormalizer.IsNearSquarePixelSar(sar));
+
         [Fact]
         public void GetMediaInfo_MetaData_Success()
         {
@@ -123,6 +140,7 @@ namespace Jellyfin.MediaEncoding.Tests.Probing
             Assert.Equal(358, res.VideoStream.Height);
             Assert.Equal(720, res.VideoStream.Width);
             Assert.Equal("2.40:1", res.VideoStream.AspectRatio);
+            Assert.True(res.VideoStream.IsAnamorphic); // SAR 32:27 — genuinely anamorphic NTSC DVD 16:9
             Assert.Equal("yuv420p", res.VideoStream.PixelFormat);
             Assert.Equal(31d, res.VideoStream.Level);
             Assert.Equal(1, res.VideoStream.RefFrames);