From c832c8e860a573396d59e3f082c2c335796c7c09 Mon Sep 17 00:00:00 2001
From: Jason Dove <jason@jasondove.me>
Date: Fri, 24 Feb 2023 15:45:30 -0600
Subject: [PATCH] prioritize default audio tracks (#1178)

---
 CHANGELOG.md                                 |  4 ++-
 ErsatzTV.Core/FFmpeg/FFmpegStreamSelector.cs | 32 ++++++++++++++------
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6f5f844fc..fda5403f8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
- Changelog
+# Changelog
 All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
@@ -17,6 +17,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   - Streaming from disk is preferred, so every playback attempt will first check the local file system
 - Use libvpl instead of libmfx to provide intel acceleration in vaapi docker images
 - Search queries no longer remove duplicate results as this was causing incorrect behavior
+- Prioritize audio streams that are flagged as "default" over number of audio channels
+    - For example, a video with a stereo commentary track and a mono "default" track will now prefer the "default" track
 
 ## [0.7.4-beta] - 2023-02-12
 ### Added
diff --git a/ErsatzTV.Core/FFmpeg/FFmpegStreamSelector.cs b/ErsatzTV.Core/FFmpeg/FFmpegStreamSelector.cs
index bec6c14ea..e5f5e1a9b 100644
--- a/ErsatzTV.Core/FFmpeg/FFmpegStreamSelector.cs
+++ b/ErsatzTV.Core/FFmpeg/FFmpegStreamSelector.cs
@@ -199,7 +199,7 @@ public class FFmpegStreamSelector : IFFmpegStreamSelector
 
     private Option<MediaStream> DefaultSelectAudioStream(
         MediaVersion version,
-        List<string> preferredLanguageCodes,
+        IReadOnlyCollection<string> preferredLanguageCodes,
         string preferredAudioTitle)
     {
         var audioStreams = version.Streams.Filter(s => s.MediaStreamKind == MediaStreamKind.Audio).ToList();
@@ -232,8 +232,7 @@ public class FFmpegStreamSelector : IFFmpegStreamSelector
     {
         if (string.IsNullOrWhiteSpace(title))
         {
-            _logger.LogDebug("No audio title has been specified; selecting stream with most channels");
-            return streams.OrderByDescending(s => s.Channels).ThenByDescending(s => s.Default).Head();
+            return PrioritizeDefault(streams);
         }
 
         // prioritize matching titles
@@ -243,18 +242,31 @@ public class FFmpegStreamSelector : IFFmpegStreamSelector
         if (matchingTitle.Any())
         {
             _logger.LogDebug(
-                "Found {Count} audio streams with preferred title {Title}; selecting stream with most channels",
+                "Found {Count} audio streams with preferred title {Title}",
                 matchingTitle.Count,
                 title);
 
-            return matchingTitle.OrderByDescending(s => s.Channels).ThenByDescending(s => s.Default).Head();
+            return PrioritizeDefault(streams);
+        }
+        
+        _logger.LogDebug("Unable to find audio stream with preferred title {Title}", title);
+
+        return PrioritizeDefault(streams);
+    }
+
+    private Option<MediaStream> PrioritizeDefault(IReadOnlyCollection<MediaStream> streams)
+    {
+        var sorted = streams.OrderByDescending(s => s.Channels).ToList();
+        Option<MediaStream> maybeDefault = Optional(sorted.Find(s => s.Default));
+        foreach (MediaStream stream in maybeDefault)
+        {
+            _logger.LogDebug("Found audio stream flagged as default");
+            return stream;
         }
 
-        _logger.LogDebug(
-            "Unable to find audio stream with preferred title {Title}; selecting stream with most channels",
-            title);
+        _logger.LogDebug("Unable to find default audio stream; selecting stream with most channels");
 
-        return streams.OrderByDescending(s => s.Channels).ThenByDescending(s => s.Default).Head();
+        return streams.HeadOrNone();
     }
 
     private async Task<Option<MediaStream>> SelectEpisodeAudioStream(
@@ -310,7 +322,7 @@ public class FFmpegStreamSelector : IFFmpegStreamSelector
         _logger.LogDebug("Checking for JS Script at {Path}", jsScriptPath);
         if (!_localFileSystem.FileExists(jsScriptPath))
         {
-            _logger.LogWarning("Unable to locate movie audio stream selector script; falling back to built-in logic");
+            _logger.LogInformation("Unable to locate movie audio stream selector script; falling back to built-in logic");
             return Option<MediaStream>.None;
         }