Expect YouTube to provide 3-letter language codes by itself sometimes

YoutubeExplode.Converter/Converter.cs

@@ -137,7 +137,7 @@ private async ValueTask ProcessAsync(
             // three-letter codes, so we'll try to convert to that first.
             var languageCode =
                 subtitleInput.Info.Language.TryGetThreeLetterCode()
-                ?? subtitleInput.Info.Language.GetTwoLetterCode();
+                ?? subtitleInput.Info.Language.Code;
 
             arguments
                 .Add($"-metadata:s:s:{i}")

YoutubeExplode.Converter/Utils/Extensions/LanguageExtensions.cs

@@ -1,17 +1,23 @@
-using YoutubeExplode.Videos.ClosedCaptions;
+using System;
+using YoutubeExplode.Videos.ClosedCaptions;
 
 namespace YoutubeExplode.Converter.Utils.Extensions;
 
 internal static class LanguageExtensions
 {
-    public static string GetTwoLetterCode(this Language language)
+    public static string? TryGetThreeLetterCode(this Language language)
     {
-        var dashIndex = language.Code.IndexOf('-');
-        return dashIndex >= 0 ? language.Code[..dashIndex] : language.Code;
-    }
+        // YouTube provides either a two-letter or a three-letter language code,
+        // which may or may not also contain a region identifier.
+        var regionNeutralLanguageCode = language
+            .Code
+            .SubstringUntil("-", StringComparison.OrdinalIgnoreCase);
+
+        // Already a three-letter code
+        if (regionNeutralLanguageCode.Length == 3)
+            return regionNeutralLanguageCode;
 
-    public static string? TryGetThreeLetterCode(this Language language) =>
-        language.GetTwoLetterCode().ToLowerInvariant() switch
+        return regionNeutralLanguageCode.ToLowerInvariant() switch
         {
             "aa" => "aar",
             "ab" => "abk",
@@ -205,4 +211,5 @@ public static string GetTwoLetterCode(this Language language)
             "zu" => "zul",
             _ => null
         };
+    }
 }

YoutubeExplode.Converter/Utils/Extensions/StringExtensions.cs

@@ -1,7 +1,19 @@
-namespace YoutubeExplode.Converter.Utils.Extensions;
+using System;
+
+namespace YoutubeExplode.Converter.Utils.Extensions;
 
 internal static class StringExtensions
 {
     public static string? NullIfWhiteSpace(this string s) =>
         !string.IsNullOrWhiteSpace(s) ? s : null;
+
+    public static string SubstringUntil(
+        this string str,
+        string sub,
+        StringComparison comparison = StringComparison.Ordinal
+    )
+    {
+        var index = str.IndexOf(sub, comparison);
+        return index < 0 ? str : str[..index];
+    }
 }

YoutubeExplode/Utils/Extensions/StringExtensions.cs

@@ -18,7 +18,6 @@ public static string SubstringUntil(
     )
     {
         var index = str.IndexOf(sub, comparison);
-
         return index < 0 ? str : str[..index];
     }
 

YoutubeExplode/Videos/ClosedCaptions/Language.cs

@@ -9,7 +9,8 @@ namespace YoutubeExplode.Videos.ClosedCaptions;
 public readonly partial struct Language
 {
     /// <summary>
-    /// Two-letter (ISO 639-1) language code, possibly with a regional identifier (e.g. 'en' or 'en-US').
+    /// Two-letter or three-letter language code, possibly with a regional identifier
+    /// (e.g. 'en' or 'en-US' or 'eng').
     /// </summary>
     public string Code { get; }