feat(translate): keep translated subtitles next to the video so they load on reopen (#14)

Co-authored-by: Tri Vo Khac <git@trivk.dev>

src/mpv/trackselection.h

@@ -28,11 +28,18 @@ bool sameLanguage(const QString &a, const QString &b);
 int pickAudio(const QList<Track> &tracks, const QStringList &preferredLanguages, int currentId);
 
 // The subtitle to turn on when the file opens. A track in one of \a preferredLanguages
-// wins over mpv's own choice \a currentId; without one, \a currentId is kept. When mpv
-// chose nothing and \a fallback is set, picks a full (not forced) subtitle in the first
-// of \a fallbackLanguages that has one, then one flagged default, then the first one.
-// Text subtitles win over bitmap ones in the same step. Returns 0 for no subtitle.
-int pickSubtitle(const QList<Track> &tracks, const QStringList &preferredLanguages, const QStringList &fallbackLanguages, int currentId, bool fallback);
+// wins over mpv's own choice \a currentId. Next comes \a translationId, the file's
+// saved translation, when \a fallback is set; without either, \a currentId is kept.
+// When mpv chose nothing and \a fallback is set, picks a full (not forced) subtitle in
+// the first of \a fallbackLanguages that has one, then one flagged default, then the
+// first one. Text subtitles win over bitmap ones in the same step. Returns 0 for no
+// subtitle.
+int pickSubtitle(const QList<Track> &tracks,
+                 const QStringList &preferredLanguages,
+                 const QStringList &fallbackLanguages,
+                 int currentId,
+                 bool fallback,
+                 int translationId = 0);
 
 // The subtitle to translate: \a currentId when it is a text subtitle, else a full text
 // subtitle in the first of \a sourceLanguages that has one, then one flagged default,