feat: add subtitle track selection, secondary subtitle and delay

src/mpv/mpvitem.h

@@ -3,6 +3,7 @@
 #include <MpvAbstractItem>
 
 #include <QUrl>
+#include <QVariantList>
 #include <QtQml/qqmlregistration.h>
 
 // QML video surface backed by libmpv (through MpvQt).
@@ -19,6 +20,14 @@ class MpvItem : public MpvAbstractItem
     Q_PROPERTY(bool paused READ paused WRITE setPaused NOTIFY pausedChanged)
     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".
+    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)
+    // In seconds; applied to both subtitles so a translation stays in sync with its source.
+    Q_PROPERTY(double subtitleDelay READ subtitleDelay WRITE setSubtitleDelay NOTIFY subtitleDelayChanged)
+
 public:
     explicit MpvItem(QQuickItem *parent = nullptr);
     ~MpvItem() override = default;
@@ -31,9 +40,21 @@ public:
     void setPaused(bool paused);
     bool isFileLoaded() const;
 
+    QVariantList subtitleTracks() const;
+    int subtitleId() const;
+    void setSubtitleId(int id);
+    int secondarySubtitleId() const;
+    void setSecondarySubtitleId(int id);
+    double subtitleDelay() const;
+    void setSubtitleDelay(double seconds);
+
     Q_INVOKABLE void loadFile(const QUrl &url);
     Q_INVOKABLE void togglePause();
     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 short message on mpv's on-screen display.
+    Q_INVOKABLE void showText(const QString &text);
 
 Q_SIGNALS:
     void currentUrlChanged();
@@ -42,10 +63,13 @@ Q_SIGNALS:
     void durationChanged();
     void pausedChanged();
     void fileLoadedChanged();
+    void subtitleTracksChanged();
+    void subtitleDelayChanged();
 
 private:
     void onPropertyChanged(const QString &property, const QVariant &value);
     void setFileLoaded(bool loaded);
+    void updateTracks(const QVariantList &trackList);
 
     bool m_ready = false;
     QUrl m_pendingUrl;
@@ -55,4 +79,8 @@ private:
     double m_duration = 0.0;
     bool m_paused = false;
     bool m_fileLoaded = false;
+    QVariantList m_subtitleTracks;
+    int m_subtitleId = 0;
+    int m_secondarySubtitleId = 0;
+    double m_subtitleDelay = 0.0;
 };