feat: translate subtitles with an OpenAI-compatible LLM

src/mpv/mpvitem.h

@@ -21,7 +21,8 @@ class MpvItem : public MpvAbstractItem
     Q_PROPERTY(bool fileLoaded READ isFileLoaded NOTIFY fileLoadedChanged)
 
     // Subtitle tracks of the current file, each a map with id, title, lang, codec,
-    // external and externalFilename. Track id 0 means "no subtitle".
+    // external, externalFilename and ffIndex (FFmpeg stream index, -1 for external
+    // files). Track id 0 means "no subtitle".
     Q_PROPERTY(QVariantList subtitleTracks READ subtitleTracks NOTIFY subtitleTracksChanged)
     Q_PROPERTY(int subtitleId READ subtitleId WRITE setSubtitleId NOTIFY subtitleTracksChanged)
     Q_PROPERTY(int secondarySubtitleId READ secondarySubtitleId WRITE setSecondarySubtitleId NOTIFY subtitleTracksChanged)
@@ -53,6 +54,9 @@ public:
     Q_INVOKABLE void seek(double seconds);
     // Adds an external subtitle file and makes it the primary subtitle.
     Q_INVOKABLE void addSubtitleFile(const QUrl &url);
+    // Shows \a url as the secondary subtitle, adding it first (named \a title) unless it
+    // is already loaded.
+    Q_INVOKABLE void showSecondarySubtitleFile(const QUrl &url, const QString &title);
     // Shows a short message on mpv's on-screen display.
     Q_INVOKABLE void showText(const QString &text);
 
@@ -83,4 +87,6 @@ private:
     int m_subtitleId = 0;
     int m_secondarySubtitleId = 0;
     double m_subtitleDelay = 0.0;
+    // File added by showSecondarySubtitleFile() that should become secondary once mpv lists it.
+    QString m_pendingSecondaryPath;
 };