From 462057a4b15d826633224752da288b7726a95a87 Mon Sep 17 00:00:00 2001
From: Jason Dove <1695733+jasongdove@users.noreply.github.com>
Date: Fri, 27 Jun 2025 08:31:50 -0500
Subject: [PATCH] prioritize stream selection by language (#2079)

---
 .../FFmpeg/CustomStreamSelectorTests.cs       | 60 +++++++++++++++++--
 ErsatzTV.Core/FFmpeg/CustomStreamSelector.cs  | 35 +++++++++--
 2 files changed, 85 insertions(+), 10 deletions(-)

diff --git a/ErsatzTV.Core.Tests/FFmpeg/CustomStreamSelectorTests.cs b/ErsatzTV.Core.Tests/FFmpeg/CustomStreamSelectorTests.cs
index dd19ab28..0e1564a3 100644
--- a/ErsatzTV.Core.Tests/FFmpeg/CustomStreamSelectorTests.cs
+++ b/ErsatzTV.Core.Tests/FFmpeg/CustomStreamSelectorTests.cs
@@ -36,7 +36,8 @@ public class CustomStreamSelectorTests
                 new Subtitle { Id = 1, Language = "eng", Title = "Words", SubtitleKind = SubtitleKind.Embedded },
                 new Subtitle { Id = 2, Language = "en", Title = "Signs" },
                 new Subtitle { Id = 3, Language = "en", Title = "Songs" },
-                new Subtitle { Id = 4, Language = "en", Forced = true, SubtitleKind = SubtitleKind.Sidecar }
+                new Subtitle { Id = 4, Language = "en", Forced = true, SubtitleKind = SubtitleKind.Sidecar },
+                new Subtitle { Id = 5, Language = "jp" }
             ];
         }
 
@@ -73,9 +74,7 @@ items:
 """
 ---
 items:
-  - audio_language:
-    - "en"
-    - "eng"
+  - audio_language: ["en", "eng"]
 """;
 
             var streamSelector = new CustomStreamSelector(
@@ -584,6 +583,59 @@ items:
             }
         }
 
+        [Test]
+        public async Task Should_Select_Prioritized_Audio_Language()
+        {
+            const string YAML =
+"""
+---
+items:
+  - audio_language: ["en*","ja"]
+    audio_title_blocklist: ["riff"]
+""";
+
+            var streamSelector = new CustomStreamSelector(
+                new FakeLocalFileSystem([new FakeFileEntry(TestFileName) { Contents = YAML }]),
+                new NullLogger<CustomStreamSelector>());
+
+            StreamSelectorResult result = await streamSelector.SelectStreams(_channel, _audioVersion, _subtitles);
+
+            result.AudioStream.IsSome.ShouldBeTrue();
+
+            foreach (MediaStream audioStream in result.AudioStream)
+            {
+                audioStream.Index.ShouldBe(2);
+                audioStream.Language.ShouldBe("eng");
+            }
+        }
+
+        [Test]
+        public async Task Should_Select_Prioritized_Subtitle_Language()
+        {
+            const string YAML =
+"""
+---
+items:
+  - audio_language:
+    - "*"
+    subtitle_language: ["jp","en*"]
+""";
+
+            var streamSelector = new CustomStreamSelector(
+                new FakeLocalFileSystem([new FakeFileEntry(TestFileName) { Contents = YAML }]),
+                new NullLogger<CustomStreamSelector>());
+
+            StreamSelectorResult result = await streamSelector.SelectStreams(_channel, _audioVersion, _subtitles);
+
+            result.Subtitle.IsSome.ShouldBeTrue();
+
+            foreach (Subtitle subtitle in result.Subtitle)
+            {
+                subtitle.Id.ShouldBe(5);
+                subtitle.Language.ShouldBe("jp");
+            }
+        }
+
         private static MediaItemAudioVersion GetTestAudioVersion(string englishLanguage)
         {
             var mediaItem = new OtherVideo();
diff --git a/ErsatzTV.Core/FFmpeg/CustomStreamSelector.cs b/ErsatzTV.Core/FFmpeg/CustomStreamSelector.cs
index 63570320..f9f60cd8 100644
--- a/ErsatzTV.Core/FFmpeg/CustomStreamSelector.cs
+++ b/ErsatzTV.Core/FFmpeg/CustomStreamSelector.cs
@@ -33,8 +33,8 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
 
             foreach (StreamSelectorItem streamSelectorItem in streamSelector.Items)
             {
-                var candidateAudioStreams = audioStreams.ToList();
-                var candidateSubtitles = allSubtitles.ToList();
+                var candidateAudioStreams = audioStreams.ToDictionary(a => a, _ => int.MaxValue);
+                var candidateSubtitles = allSubtitles.ToDictionary(s => s, _ => int.MaxValue);
 
                 // try to find matching audio stream
                 foreach (MediaStream audioStream in audioStreams.ToList())
@@ -45,8 +45,10 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
                     if (streamSelectorItem.AudioLanguages.Count > 0)
                     {
                         // match any of the listed languages
-                        foreach (string audioLanguage in streamSelectorItem.AudioLanguages)
+                        for (var langIndex = 0; langIndex < streamSelectorItem.AudioLanguages.Count; langIndex++)
                         {
+                            string audioLanguage = streamSelectorItem.AudioLanguages[langIndex];
+
                             // special case
                             if (audioLanguage == "*")
                             {
@@ -56,6 +58,12 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
                             matches = matches || FileSystemName.MatchesSimpleExpression(
                                 audioLanguage.ToLowerInvariant(),
                                 audioStream.Language.ToLowerInvariant());
+
+                            // store lang index for prioritizing later
+                            if (matches && candidateAudioStreams[audioStream] == int.MaxValue)
+                            {
+                                candidateAudioStreams[audioStream] = langIndex;
+                            }
                         }
                     }
                     else
@@ -121,8 +129,10 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
                         if (streamSelectorItem.SubtitleLanguages.Count > 0)
                         {
                             // match any of the listed languages
-                            foreach (string subtitleLanguage in streamSelectorItem.SubtitleLanguages)
+                            for (var langIndex = 0; langIndex < streamSelectorItem.SubtitleLanguages.Count; langIndex++)
                             {
+                                string subtitleLanguage = streamSelectorItem.SubtitleLanguages[langIndex];
+
                                 // special case
                                 if (subtitleLanguage == "*")
                                 {
@@ -132,6 +142,12 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
                                 matches = matches || FileSystemName.MatchesSimpleExpression(
                                     subtitleLanguage,
                                     subtitle.Language);
+
+                                // store lang index for prioritizing later
+                                if (matches && candidateSubtitles[subtitle] == int.MaxValue)
+                                {
+                                    candidateSubtitles[subtitle] = langIndex;
+                                }
                             }
                         }
                         else
@@ -183,8 +199,15 @@ public class CustomStreamSelector(ILocalFileSystem localFileSystem, ILogger<Cust
                     }
                 }
 
-                Option<MediaStream> maybeAudioStream = candidateAudioStreams.HeadOrNone();
-                Option<Subtitle> maybeSubtitle = candidateSubtitles.HeadOrNone();
+                Option<MediaStream> maybeAudioStream = candidateAudioStreams
+                    .OrderBy(a => a.Value)
+                    .Select(a => a.Key)
+                    .HeadOrNone();
+
+                Option<Subtitle> maybeSubtitle = candidateSubtitles
+                    .OrderBy(s => s.Value)
+                    .Select(s => s.Key)
+                    .HeadOrNone();
 
                 if (maybeAudioStream.IsSome)
                 {