fix watermark opacity filter (#820)

CHANGELOG.md

@@ -6,6 +6,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ## [Unreleased]
 ### Fixed
 - Additional fix for duplicate `Other Videos` entries; trash may need to be emptied one last time after upgrading
+- Fix watermark opacity in cultures where `,` is a decimal separator
 
 ### Added
 - Enable QSV hardware acceleration for vaapi docker images

ErsatzTV.FFmpeg.Tests/Filter/WatermarkOpacityFilterTests.cs

@@ -0,0 +1,47 @@
+using System.Collections.Generic;
+using ErsatzTV.FFmpeg.Filter;
+using ErsatzTV.FFmpeg.State;
+using FluentAssertions;
+using LanguageExt;
+using NUnit.Framework;
+
+namespace ErsatzTV.FFmpeg.Tests.Filter;
+
+[TestFixture]
+public class WatermarkOpacityFilterTests
+{
+    [Test]
+    // this needs to be a culture where ',' is a decimal separator
+    [SetCulture("it-IT")]
+    public void Should_Return_Filter_With_Period_Decimal_Unlike_Local_Culture()
+    {
+        var filter = new WatermarkOpacityFilter(
+            new WatermarkState(
+                Option<List<WatermarkFadePoint>>.None,
+                WatermarkLocation.BottomRight,
+                WatermarkSize.ActualSize,
+                50,
+                50,
+                50,
+                75));
+
+        filter.Filter.Should().Be("colorchannelmixer=aa=0.75");
+    }
+
+    [Test]
+    [SetCulture("en-US")]
+    public void Should_Return_Filter_With_Period_Decimal()
+    {
+        var filter = new WatermarkOpacityFilter(
+            new WatermarkState(
+                Option<List<WatermarkFadePoint>>.None,
+                WatermarkLocation.BottomRight,
+                WatermarkSize.ActualSize,
+                50,
+                50,
+                50,
+                75));
+
+        filter.Filter.Should().Be("colorchannelmixer=aa=0.75");
+    }
+}

ErsatzTV.FFmpeg/Filter/WatermarkOpacityFilter.cs

@@ -1,4 +1,5 @@
-using ErsatzTV.FFmpeg.State;
+using System.Globalization;
+using ErsatzTV.FFmpeg.State;
 
 namespace ErsatzTV.FFmpeg.Filter;
 
@@ -13,7 +14,7 @@ public class WatermarkOpacityFilter : BaseFilter
         get
         {
             double opacity = _desiredState.Opacity / 100.0;
-            return $"colorchannelmixer=aa={opacity:F2}";
+            return $"colorchannelmixer=aa={opacity.ToString("F2", NumberFormatInfo.InvariantInfo)}";
         }
     }