Handle forced AV subtitles without needing a forced track to be selected

This improves the behaviour of mythfrontend in its automatic handling of
forced subtitle tracks. The previous behaviour relied on automatically
selecting the forced track as a default for the user's preference. The new
behaviour attempts to find a non-forced track for the user's preference and
changes the subtitle toggle feature to be between forced and non-forced,
rather than on and off.

mythtv/libs/libmythtv/decoders/avformatdecoder.cpp

@@ -3916,6 +3916,7 @@ bool AvFormatDecoder::ProcessSubtitlePacket(AVStream *curstream, AVPacket *pkt)
 
     m_trackLock.lock();
     int subIdx = m_selectedTrack[kTrackTypeSubtitle].m_av_stream_index;
+    int forcedSubIdx = m_selectedForcedSubtitleTrack.m_av_stream_index;
     bool isForcedTrack = m_selectedTrack[kTrackTypeSubtitle].m_forced;
     m_trackLock.unlock();
 
@@ -3941,7 +3942,8 @@ bool AvFormatDecoder::ProcessSubtitlePacket(AVStream *curstream, AVPacket *pkt)
             }
         }
     }
-    else if (m_decodeAllSubtitles || pkt->stream_index == subIdx)
+    else if (m_decodeAllSubtitles || pkt->stream_index == subIdx
+                                  || pkt->stream_index == forcedSubIdx)
     {
         m_avCodecLock.lock();
         AVCodecContext *ctx = m_codecMap.GetCodecContext(curstream);
@@ -3950,6 +3952,9 @@ bool AvFormatDecoder::ProcessSubtitlePacket(AVStream *curstream, AVPacket *pkt)
 
         subtitle.start_display_time += pts;
         subtitle.end_display_time += pts;
+
+        if (pkt->stream_index == forcedSubIdx)
+            isForcedTrack = true;
     }
 
     if (gotSubtitles)

mythtv/libs/libmythtv/decoders/decoderbase.cpp

@@ -1144,6 +1144,24 @@ int DecoderBase::AutoSelectTrack(uint Type)
     {
         // Find best track favoring forced.
         selTrack = BestTrack(Type, true);
+
+        if (Type == kTrackTypeSubtitle)
+        {
+            if (m_tracks[Type][selTrack].m_forced)
+            {
+                // A forced AV Subtitle tracks is handled without the user
+                // explicitly enabling subtitles. Try to find a good non-forced
+                // track that can be swapped to in the case the user does
+                // explicitly enable subtitles.
+                int nonForcedTrack = BestTrack(Type, false);
+
+                if (!m_tracks[Type][nonForcedTrack].m_forced)
+                {
+                    m_selectedForcedSubtitleTrack = m_tracks[Type][selTrack];
+                    selTrack = nonForcedTrack;
+                }
+            }
+        }
     }
 
     int oldTrack = m_currentTrack[Type];

mythtv/libs/libmythtv/decoders/decoderbase.h

@@ -361,6 +361,7 @@ class DecoderBase
     std::array<sinfo_vec_t,kTrackTypeCount> m_tracks;
     std::array<StreamInfo, kTrackTypeCount> m_wantedTrack;
     std::array<StreamInfo, kTrackTypeCount> m_selectedTrack;
+    StreamInfo           m_selectedForcedSubtitleTrack;
 
     /// language preferences for auto-selection of streams
     std::vector<int>     m_languagePreference;