fix: Snapshots from rotated videos should have correct width/height

Some video-files have their metadata as -90 instead of 90. This PR handles correct aspect-ratio and rotation when taking snapshots.

The sample video provided in the PR is my own recording. A bit too big maybe? I couldn't find any command to set the metadata to `-90` on existing video. Would be happy to get it working on already existing test-data to reduce size.

Fixes #509

FFMpegCore.Test/FFMpegCore.Test.csproj

@@ -51,6 +51,9 @@
     <None Update="Resources\input_3sec_rotation_90deg.mp4">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>
+    <None Update="Resources\input_3sec_rotation_negative_90deg.mp4">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
     <None Update="Resources\input_audio_only_10sec.mp4">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>

FFMpegCore.Test/FFProbeTests.cs

@@ -145,6 +145,13 @@ public void Probe_Rotation()
             Assert.AreEqual(90, info.PrimaryVideoStream.Rotation);
         }
 
+        [TestMethod]
+        public void Probe_Rotation_Negative_Value()
+        {
+            var info = FFProbe.Analyse(TestResources.Mp4VideoRotationNegative);
+            Assert.AreEqual(-90, info.PrimaryVideoStream.Rotation);
+        }
+
         [TestMethod, Timeout(10000)]
         public async Task Probe_Async_Success()
         {

FFMpegCore.Test/Resources/TestResources.cs

@@ -4,6 +4,7 @@ public static class TestResources
     {
         public static readonly string Mp4Video = "./Resources/input_3sec.mp4";
         public static readonly string Mp4VideoRotation = "./Resources/input_3sec_rotation_90deg.mp4";
+        public static readonly string Mp4VideoRotationNegative = "./Resources/input_3sec_rotation_negative_90deg.mp4";
         public static readonly string WebmVideo = "./Resources/input_3sec.webm";
         public static readonly string Mp4WithoutVideo = "./Resources/input_audio_only_10sec.mp4";
         public static readonly string Mp4WithoutAudio = "./Resources/input_video_only_3sec.mp4";

FFMpegCore.Test/VideoTest.cs

@@ -480,6 +480,21 @@ public void Video_Snapshot_PersistSnapshot()
             Assert.AreEqual("png", analysis.PrimaryVideoStream!.CodecName);
         }
 
+        [TestMethod, Timeout(BaseTimeoutMilliseconds)]
+        public void Video_Snapshot_Rotated_PersistSnapshot()
+        {
+            using var outputPath = new TemporaryFile("out.png");
+            var input = FFProbe.Analyse(TestResources.Mp4VideoRotationNegative);
+
+            FFMpeg.Snapshot(TestResources.Mp4VideoRotationNegative, outputPath);
+
+            var analysis = FFProbe.Analyse(outputPath);
+            // height and width should be swapped
+            Assert.AreEqual(input.PrimaryVideoStream!.Height, analysis.PrimaryVideoStream!.Width);
+            Assert.AreEqual(input.PrimaryVideoStream.Width, analysis.PrimaryVideoStream!.Height);
+            Assert.AreEqual("png", analysis.PrimaryVideoStream!.CodecName);
+        }
+
         [TestMethod, Timeout(BaseTimeoutMilliseconds)]
         public void Video_GifSnapshot_PersistSnapshot()
         {

FFMpegCore/FFMpeg/SnapshotArgumentBuilder.cs

@@ -64,7 +64,7 @@ public static (FFMpegArguments, Action<FFMpegArgumentOptions> outputOptions) Bui
         }
 
         var currentSize = new Size(source.PrimaryVideoStream.Width, source.PrimaryVideoStream.Height);
-        if (source.PrimaryVideoStream.Rotation == 90 || source.PrimaryVideoStream.Rotation == 180)
+        if (IsRotated(source.PrimaryVideoStream.Rotation))
         {
             currentSize = new Size(source.PrimaryVideoStream.Height, source.PrimaryVideoStream.Width);
         }
@@ -88,4 +88,10 @@ public static (FFMpegArguments, Action<FFMpegArgumentOptions> outputOptions) Bui
 
         return null;
     }
+
+    private static bool IsRotated(int rotation)
+    {
+        var absRotation = Math.Abs(rotation);
+        return absRotation == 90 || absRotation == 180;
+    }
 }