Fix subtitle stream selection for vobsubs with multiple streams

Until now, we've always assumed that a subtitle file contains exactly 1
subtitle. This is not true with some vobsub files. We have to abandon
the current simplistic way of selecting streams. Instead, check the
stream list as returned by the player directly, and select the wanted
streams explicitly.

Requires a corresponding web-client change to work, but is backwards
compatible.

src/player/PlayerComponent.cpp

@@ -148,8 +148,8 @@ bool PlayerComponent::componentInitialize()
   // (See handler in handleMpvEvent() for details.)
   mpv::qt::command_variant(m_mpv, QStringList() << "hook-add" << "on_load" << "1" << "0");
 
-  // Setup a hook with the ID 1, which is run at a certain stage during loading.
-  // We use it to probe the codecs.
+  // Setup a hook with the ID 2, which is run at a certain stage during loading.
+  // We use it to initialize stream selections and to probe the codecs.
   mpv::qt::command_variant(m_mpv, QStringList() << "hook-add" << "on_preloaded" << "2" << "0");
 
   updateAudioDeviceList();
@@ -242,32 +242,16 @@ void PlayerComponent::queueMedia(const QString& url, const QVariantMap& options,
   if (startMilliseconds != 0)
     extraArgs.insert("start", "+" + QString::number(startMilliseconds / 1000.0));
 
-  // force default audio selection
-  extraArgs.insert("ff-aid", "auto");
-
-  // by default ignore all subtitles, unless overridden
+  // we're going to select these streams later, in the preloaded hook
+  extraArgs.insert("aid", "no");
   extraArgs.insert("sid", "no");
-  extraArgs.insert("ff-sid", "auto");
 
-  // detect subtitles
-  if (!subtitleStream.isEmpty())
-  {
-    // If the stream title starts with a #, then it's an index
-    if (subtitleStream.startsWith("#"))
-      extraArgs.insert("ff-sid", subtitleStream.mid(1));
-    else {
-      extraArgs.insert("sub-file", subtitleStream);
-      extraArgs.insert("sid", "auto"); // select the external one by default
-    }
-  }
+  m_currentSubtitleStream = subtitleStream;
+  m_currentAudioStream = audioStream;
 
   if (metadata["type"] == "music")
     extraArgs.insert("vid", "no");
 
-  // and then the audio stream
-  if (!audioStream.isEmpty())
-    extraArgs.insert("ff-aid", audioStream);
-
   extraArgs.insert("pause", options["autoplay"].toBool() ? "no" : "yes");
 
   QString userAgent = metadata["headers"].toMap()["User-Agent"].toString();
@@ -553,10 +537,12 @@ void PlayerComponent::handleMpvEvent(mpv_event *event)
         }
         break;
       }
-      // Start "on_preload" hook.
-      // Used to probe codecs.
+      // Start "on_preloaded" hook.
+      // Used initialize stream selections and to probe codecs.
       if (!strcmp(msg->args[1], "2"))
       {
+        reselectStream(m_currentSubtitleStream, MediaType::Subtitle);
+        reselectStream(m_currentAudioStream, MediaType::Audio);
         startCodecsLoading([=] {
           mpv::qt::command_variant(m_mpv, QStringList() << "hook-ack" << resumeId);
         });
@@ -675,30 +661,125 @@ bool PlayerComponent::muted()
 }
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
-void PlayerComponent::setSubtitleStream(const QString &subtitleStream)
+QVariantList PlayerComponent::findStreamsForURL(const QString &url)
 {
-  if (subtitleStream.isEmpty())
+  bool isExternal = !url.isEmpty();
+  QVariantList res;
+
+  auto tracks = mpv::qt::get_property_variant(m_mpv, "track-list");
+  for (auto track : tracks.toList())
   {
-    mpv::qt::set_property_variant(m_mpv, "ff-sid", "no");
+    QVariantMap map = track.toMap();
+
+    if (map["external"].toBool() != isExternal)
+      continue;
+
+    if (!isExternal || map["external-filename"].toString() == url)
+      res += map;
   }
-  else if (subtitleStream.startsWith("#"))
+
+  return res;
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+void PlayerComponent::reselectStream(const QString &streamSelection, MediaType target)
+{
+  QString streamIdPropertyName;
+  QString streamAddCommandName;
+  QString mpvStreamTypeName;
+
+  switch (target)
+  {
+  case MediaType::Subtitle:
+    mpvStreamTypeName = "sub";
+    streamIdPropertyName = "sid";
+    streamAddCommandName = "sub-add";
+    break;
+  case MediaType::Audio:
+    mpvStreamTypeName = "audio";
+    streamIdPropertyName = "aid";
+    streamAddCommandName = "audio-add";
+    break;
+  }
+
+  if (streamSelection.isEmpty())
   {
-    mpv::qt::set_property_variant(m_mpv, "ff-sid", subtitleStream.mid(1));
+    mpv::qt::set_property_variant(m_mpv, streamIdPropertyName, "no");
+    return;
+  }
+
+  QString streamName;
+  QString streamID;
+
+  if (streamSelection.startsWith("#"))
+  {
+    int splitPos = streamSelection.indexOf(",");
+    if (splitPos < 0)
+    {
+      // Stream from the main file
+      streamID = streamSelection.mid(1);
+      streamName = "";
+    }
+    else
+    {
+      // Stream from an external file
+      streamID = streamSelection.mid(1, splitPos - 1);
+      streamName = streamSelection.mid(splitPos + 1);
+    }
   }
   else
   {
-    QStringList args = (QStringList() << "sub-add" << subtitleStream << "cached");
-    mpv::qt::command_variant(m_mpv, args);
+    if (target == MediaType::Audio)
+    {
+      // For some reason, audio stream selections never start with '#'.
+      streamID = streamSelection;
+      streamName = "";
+    }
+    else
+    {
+      // Legacy web-client single external subtitle
+      streamID = "0";
+      streamName = streamSelection;
+    }
+  }
+
+  if (!streamName.isEmpty())
+  {
+    auto streams = findStreamsForURL(streamName);
+    if (streams.isEmpty())
+    {
+      QStringList args = (QStringList() << streamAddCommandName << streamName);
+      mpv::qt::command_variant(m_mpv, args);
+    }
+  }
+
+  for (auto stream : findStreamsForURL(streamName))
+  {
+    auto map = stream.toMap();
+
+    if (map["type"].toString() != mpvStreamTypeName)
+      continue;
+
+    if (map["ff-index"].toString() == streamID)
+    {
+      mpv::qt::set_property_variant(m_mpv, streamIdPropertyName, map["id"]);
+      break;
+    }
   }
 }
 
+///////////////////////////////////////////////////////////////////////////////////////////////////
+void PlayerComponent::setSubtitleStream(const QString &subtitleStream)
+{
+  m_currentSubtitleStream = subtitleStream;
+  reselectStream(m_currentSubtitleStream, MediaType::Subtitle);
+}
+
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 void PlayerComponent::setAudioStream(const QString &audioStream)
 {
-  if (audioStream.isEmpty())
-    mpv::qt::set_property_variant(m_mpv, "ff-aid", "no");
-  else
-    mpv::qt::set_property_variant(m_mpv, "ff-aid", audioStream);
+  m_currentAudioStream = audioStream;
+  reselectStream(m_currentAudioStream, MediaType::Audio);
 }
 
 /////////////////////////////////////////////////////////////////////////////////////////

src/player/PlayerComponent.h

@@ -126,6 +126,11 @@ public:
     playing,
     buffering,
   };
+
+  enum class MediaType {
+    Subtitle,
+    Audio,
+  };
   
 public Q_SLOTS:
   void setAudioConfiguration();
@@ -187,6 +192,8 @@ private:
   // Call resume() when done.
   void startCodecsLoading(std::function<void()> resume);
   void updateVideoAspectSettings();
+  QVariantList findStreamsForURL(const QString &url);
+  void reselectStream(const QString &streamSelection, MediaType target);
 
   mpv::qt::Handle m_mpv;
 
@@ -211,6 +218,8 @@ private:
   bool m_doAc3Transcoding;
   QStringList m_passthroughCodecs;
   QVariantMap m_serverMediaInfo;
+  QString m_currentSubtitleStream;
+  QString m_currentAudioStream;
 };
 
 #endif // PLAYERCOMPONENT_H