feat(mux): add muxing.default_language to override default track per type

Allows users to force a preferred audio/video/subtitle language as the MKV default track regardless of the title's original_language. Each track type falls back to its previous default rule when no match is found.

unshackle/core/tracks/tracks.py

@@ -428,13 +428,40 @@ class Tracks:
         if config.muxing.get("set_title", True):
             cl.extend(["--title", title])
 
+        default_language = config.muxing.get("default_language") or {}
+        preferred_video_lang = default_language.get("video")
+        preferred_audio_lang = default_language.get("audio")
+        preferred_subtitle_lang = default_language.get("subtitle")
+
+        preferred_video_idx: Optional[int] = None
+        if preferred_video_lang:
+            preferred_video_idx = next(
+                (idx for idx, v in enumerate(self.videos) if is_close_match(v.language, [preferred_video_lang])),
+                None,
+            )
+
+        preferred_audio_idx: Optional[int] = None
+        if preferred_audio_lang:
+            preferred_audio_idx = next(
+                (idx for idx, a in enumerate(self.audio) if is_close_match(a.language, [preferred_audio_lang])),
+                None,
+            )
+
+        preferred_subtitle_idx: Optional[int] = None
+        if preferred_subtitle_lang and not skip_subtitles:
+            preferred_subtitle_idx = next(
+                (idx for idx, s in enumerate(self.subtitles) if is_close_match(s.language, [preferred_subtitle_lang])),
+                None,
+            )
+
         for i, vt in enumerate(self.videos):
             if not vt.path or not vt.path.exists():
                 raise ValueError("Video Track must be downloaded before muxing...")
             events.emit(events.Types.TRACK_MULTIPLEX, track=vt)
 
-            is_default = False
-            if title_language:
+            if preferred_video_idx is not None:
+                is_default = i == preferred_video_idx
+            elif title_language:
                 is_default = vt.language == title_language
                 if not any(v.language == title_language for v in self.videos):
                     is_default = vt.is_original_lang or i == 0
@@ -490,6 +517,10 @@ class Tracks:
             if not at.path or not at.path.exists():
                 raise ValueError("Audio Track must be downloaded before muxing...")
             events.emit(events.Types.TRACK_MULTIPLEX, track=at)
+            if preferred_audio_idx is not None:
+                audio_default = i == preferred_audio_idx
+            else:
+                audio_default = at.is_original_lang
             cl.extend(
                 [
                     "--track-name",
@@ -497,7 +528,7 @@ class Tracks:
                     "--language",
                     f"0:{at.language}",
                     "--default-track",
-                    f"0:{at.is_original_lang}",
+                    f"0:{audio_default}",
                     "--visual-impaired-flag",
                     f"0:{at.descriptive}",
                     "--original-flag",
@@ -511,10 +542,13 @@ class Tracks:
             )
 
         if not skip_subtitles:
-            for st in self.subtitles:
+            for i, st in enumerate(self.subtitles):
                 if not st.path or not st.path.exists():
                     raise ValueError("Text Track must be downloaded before muxing...")
                 events.emit(events.Types.TRACK_MULTIPLEX, track=st)
+                if preferred_subtitle_idx is not None:
+                    default = i == preferred_subtitle_idx
+                else:
                     default = bool(self.audio and is_close_match(st.language, [self.audio[0].language]) and st.forced)
                 cl.extend(
                     [

unshackle/unshackle-example.yaml

@@ -147,6 +147,19 @@ muxing:
   #   false: Separate MKV per (quality, audio_codec) combination
   #     Example: Title.1080p.AAC.mkv, Title.1080p.EC3.mkv
   merge_audio: true
+  # default_language: Override which track is flagged as the default in the muxed MKV.
+  #   audio:  BCP-47 tag of the preferred default audio track (e.g. pl, en, pt-BR).
+  #           Wins over the title's original_language. Falls back to is_original_lang
+  #           if no matching track is present.
+  #   video:  BCP-47 tag of the preferred default video track. Falls back to the
+  #           original-language / first-track rule if no match is found.
+  #   subtitle: BCP-47 tag of the preferred default subtitle track. Falls back to
+  #             the existing rule (forced sub matching the audio language) if no
+  #             matching subtitle is present.
+  # default_language:
+  #   audio: pl
+  #   video: pl
+  #   subtitle: pl
 
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