feat(download): enforce strict audio_multistream gating and enrich stream metadata

- Return `None` from `_get_audio_languages` when `audio_multistream` is
  not effectively enabled; `audio_languages` alone must not trigger
  multi-track downloads (strict mode)
- Remove `audio_languages` from MKV container-forcing logic in
- Extend `StreamItemSerializer` with optional `language`, `title`,
  `channels`, and `channel_layout` fields to surface per-track metadata
- Improve `_extract_audio_metadata` to extract language (normalising
  "und" → None), track title, channel layout, and fall back to BPS/MKV
  tags when a stream-level bitrate is absent

backend/download/src/yt_dlp_handler.py

@@ -376,7 +376,14 @@ class VideoDownloader(DownloaderBase):
             obs["audio_multistreams"] = overwrites.get("audio_multistream")
 
     def _get_audio_languages(self, channel_id: str) -> list[str] | None:
-        """get audio languages from config or channel overwrites"""
+        """get audio languages from config or channel overwrites.
+
+        Returns None if audio_multistream is not effectively enabled — audio_languages
+        alone must not force multi-track downloads (Option A / strict mode).
+        """
+        if not self._is_audio_multistream_enabled(channel_id):
+            return None
+
         overwrites = self.channel_overwrites.get(channel_id, {})
         audio_languages = overwrites.get(
             "audio_languages",

backend/video/serializers.py

@@ -60,6 +60,10 @@ class StreamItemSerializer(serializers.Serializer):
     index = serializers.IntegerField()
     type = serializers.ChoiceField(choices=["video", "audio"])
     width = serializers.IntegerField(required=False)
+    language = serializers.CharField(required=False, allow_null=True)
+    title = serializers.CharField(required=False, allow_null=True)
+    channels = serializers.IntegerField(required=False, allow_null=True)
+    channel_layout = serializers.CharField(required=False, allow_null=True)
 
 
 class SubtitleFragmentSerializer(serializers.Serializer):

backend/video/src/index.py

@@ -334,7 +334,11 @@ class YoutubeVideo(YouTubeItem, YoutubeSubtitle):
         )
 
     def _get_download_container(self) -> str:
-        """resolve container with channel overwrites"""
+        """resolve container with channel overwrites.
+
+        MKV is only forced when audio_multistream is effectively enabled.
+        audio_languages alone must not override the container (Option A / strict).
+        """
         container = self.config["downloads"].get("container", "mp4")
         channel_overwrites = self.json_data.get("channel", {}).get(
             "channel_overwrites", {}
@@ -342,17 +346,14 @@ class YoutubeVideo(YouTubeItem, YoutubeSubtitle):
         if channel_overwrites.get("download_container"):
             container = channel_overwrites.get("download_container")
 
-        # audio_languages or audio_multistream forces mkv for multi-stream support
-        audio_languages = (
-            channel_overwrites.get("audio_languages")
-            or self.config["downloads"].get("audio_languages")
-        )
+        # audio_multistream being on requires mkv for multi-track muxing.
+        # Respect channel override false explicitly (suppress global setting).
         audio_multistream = (
             channel_overwrites.get("audio_multistream")
             if channel_overwrites.get("audio_multistream") is not None
             else self.config["downloads"].get("audio_multistream")
         )
-        if audio_languages or audio_multistream:
+        if audio_multistream:
             container = "mkv"
 
         return container

backend/video/src/media_streams.py

@@ -65,12 +65,41 @@ class MediaStreamExtractor:
 
     def _extract_audio_metadata(self, stream) -> None:
         """extract audio metadata"""
+        tags = stream.get("tags", {})
+
+        # Bitrate: prefer stream-level, fall back to BPS tag (common in MKV)
+        bitrate_raw = stream.get("bit_rate")
+        if not bitrate_raw:
+            bps_tag = tags.get("BPS") or tags.get("BPS-eng") or tags.get("NUMBER_OF_BYTES")
+            if bps_tag:
+                try:
+                    bitrate_raw = int(bps_tag)
+                except (TypeError, ValueError):
+                    bitrate_raw = 0
+            else:
+                bitrate_raw = 0
+
+        language = tags.get("language") or tags.get("LANGUAGE") or None
+        # Normalise "und" (undetermined) to None
+        if language == "und":
+            language = None
+
+        track_title = tags.get("title") or tags.get("TITLE") or None
+
+        # Channels: prefer channel_layout label, fall back to channel count
+        channel_layout = stream.get("channel_layout")
+        channels = stream.get("channels")
+
         self.metadata.append(
             {
-                "bitrate": int(stream.get("bit_rate", 0)),
+                "bitrate": int(bitrate_raw),
                 "codec": stream.get("codec_name", "undefined"),
                 "index": stream["index"],
                 "type": "audio",
+                "language": language,
+                "title": track_title,
+                "channels": channels,
+                "channel_layout": channel_layout,
             }
         )
 

frontend/src/pages/ChannelAbout.tsx

@@ -14,6 +14,7 @@ import useIsAdmin from '../functions/useIsAdmin';
 import InputConfig from '../components/InputConfig';
 import ToggleConfig from '../components/ToggleConfig';
 import { useUserConfigStore } from '../stores/UserConfigStore';
+import { useAppSettingsStore } from '../stores/AppSettingsStore';
 import { ApiResponseType } from '../functions/APIClient';
 
 export type ChannelBaseOutletContextType = {
@@ -35,6 +36,7 @@ type ChannelAboutParams = {
 const ChannelAbout = () => {
   const { channelId } = useParams() as ChannelAboutParams;
   const { userConfig } = useUserConfigStore();
+  const { appSettingsConfig } = useAppSettingsStore();
   const { setStartNotification } = useOutletContext() as ChannelBaseOutletContextType;
   const navigate = useNavigate();
   const isAdmin = useIsAdmin();
@@ -129,6 +131,11 @@ const ChannelAbout = () => {
     return 'Channel not found!';
   }
 
+  // The effective container is the channel override if set, otherwise the global setting.
+  const globalContainer = appSettingsConfig.downloads.container ?? 'mp4';
+  const effectiveContainer = downloadContainer ?? globalContainer;
+  const isMkvActive = effectiveContainer === 'mkv';
+
   return (
     <>
       <title>{`TA | Channel: About ${channel.channel_name}`}</title>
@@ -342,9 +349,9 @@ const ChannelAbout = () => {
                 <ToggleConfig
                   name="audio_multistream"
                   value={audioMultistream ?? false}
-                  disabled={(downloadContainer ?? 'mp4') !== 'mkv'}
+                  disabled={!isMkvActive}
                   helperText={
-                    (downloadContainer ?? 'mp4') !== 'mkv'
+                    !isMkvActive
                       ? 'Choose mkv above (or use the global mkv setting) to enable multiple audio tracks.'
                       : 'Downloads every available audio language for this channel.'
                   }
@@ -358,19 +365,21 @@ const ChannelAbout = () => {
                   <p className="settings-error">{audioMultistreamWarning}</p>
                 )}
               </div>
-              <div className="settings-box-wrapper">
-                <div>
-                  <p>Audio Languages</p>
+              {isMkvActive && (
+                <div className="settings-box-wrapper">
+                  <div>
+                    <p>Audio Languages</p>
+                  </div>
+                  <InputConfig
+                    type="text"
+                    name="audio_languages"
+                    value={audioLanguages}
+                    setValue={setAudioLanguages}
+                    oldValue={channel.channel_overwrites?.audio_languages ?? null}
+                    updateCallback={handleUpdateConfig}
+                  />
                 </div>
-                <InputConfig
-                  type="text"
-                  name="audio_languages"
-                  value={audioLanguages}
-                  setValue={setAudioLanguages}
-                  oldValue={channel.channel_overwrites?.audio_languages ?? null}
-                  updateCallback={handleUpdateConfig}
-                />
-              </div>
+              )}
               <div className="settings-box-wrapper">
                 <div>
                   <p>

frontend/src/pages/Home.tsx

@@ -47,6 +47,10 @@ export type StreamType = {
   width?: number;
   height?: number;
   bitrate: number;
+  language?: string | null;
+  title?: string | null;
+  channels?: number | null;
+  channel_layout?: string | null;
 };
 
 export type Subtitles = {

frontend/src/pages/Video.tsx

@@ -19,7 +19,6 @@ import humanFileSize from '../functions/humanFileSize';
 import ScrollToTopOnNavigate from '../components/ScrollToTop';
 import ChannelOverview from '../components/ChannelOverview';
 import deleteVideo from '../api/actions/deleteVideo';
-import capitalizeFirstLetter from '../functions/capitalizeFirstLetter';
 import formatDate from '../functions/formatDates';
 import formatNumbers from '../functions/formatNumbers';
 import queueReindex from '../api/actions/queueReindex';
@@ -465,15 +464,40 @@ const Video = () => {
 
             {video.streams &&
               video.streams.map(stream => {
+                const bitrateDisplay =
+                  stream.bitrate > 0
+                    ? `${humanFileSize(stream.bitrate, useSiUnits)}/s`
+                    : null;
+
+                if (stream.type === 'video') {
+                  return (
+                    <p key={stream.index}>
+                      Video: {stream.codec}
+                      {bitrateDisplay && <> {bitrateDisplay}</>}
+                      {stream.width && (
+                        <>
+                          <span className="space-carrot">|</span> {stream.width}x{stream.height}
+                        </>
+                      )}
+                    </p>
+                  );
+                }
+
+                // Audio stream
+                const langLabel = stream.title || stream.language?.toUpperCase() || null;
+                const layoutLabel = stream.channel_layout || (stream.channels ? `${stream.channels}ch` : null);
+
                 return (
                   <p key={stream.index}>
-                    {capitalizeFirstLetter(stream.type)}: {stream.codec}{' '}
-                    {humanFileSize(stream.bitrate, useSiUnits)}/s
-                    {stream.width && (
+                    Audio
+                    {langLabel && <> [{langLabel}]</>}:{' '}
+                    {stream.codec}
+                    {bitrateDisplay && <> {bitrateDisplay}</>}
+                    {layoutLabel && (
                       <>
-                        <span className="space-carrot">|</span> {stream.width}x{stream.height}
+                        <span className="space-carrot">|</span> {layoutLabel}
                       </>
-                    )}{' '}
+                    )}
                   </p>
                 );
               })}