Ticket #7638: dvd-audio-stream-ordering.dpatch

diff --git a/mythtv/libs/libmythtv/avformatdecoder.cpp b/mythtv/libs/libmythtv/avformatdecoder.cpp
index ab4017d..0b2ec38 100644
--- a/mythtv/libs/libmythtv/avformatdecoder.cpp
+++ b/mythtv/libs/libmythtv/avformatdecoder.cpp
@@ -215,6 +215,43 @@ class AvFormatDecoderPrivate
 };
 
 /**
+ * \brief returns the logical audio stream id of a dvd audio stream
+ *
+ * subtracts the stream id offset based on the stream encoding
+ */
+static uint dvd_get_logical_audio_stream_id(uint stream_id)
+{
+    const uint AC3_OFFSET  = 0x80;
+    const uint DTS_OFFSET  = 0x88;
+    const uint LPCM_OFFSET = 0xA0;
+    if (stream_id >= LPCM_OFFSET)
+    {
+        return stream_id - LPCM_OFFSET;
+    }
+    else if (stream_id >= DTS_OFFSET)
+    {
+        return stream_id - DTS_OFFSET;
+    }
+    else if (stream_id >= AC3_OFFSET)
+    {
+        return stream_id - AC3_OFFSET;
+    }
+    return -1;
+}
+
+/**
+ * \brief compares dvd audio streams based on their logical stream id
+ */
+static bool dvd_audio_stream_id_comparator(
+    const StreamInfo& a,
+    const StreamInfo& b)
+{
+    return
+        dvd_get_logical_audio_stream_id(a.stream_id)
+        < dvd_get_logical_audio_stream_id(b.stream_id);
+}
+
+/**
  * \brief Initialise either libmpeg2, or DVDV (Mac HW accel), to do decoding
  *
  * Both of these are meant to be alternatives to FFMPEG,
@@ -2027,6 +2064,9 @@ int AvFormatDecoder::ScanStreams(bool novideo)
     {
         if (tracks[kTrackTypeAudio].size() > 1)
         {
+            sort(tracks[kTrackTypeAudio].begin(),
+                 tracks[kTrackTypeAudio].end(),
+                 dvd_audio_stream_id_comparator);
             sinfo_vec_t::iterator it = tracks[kTrackTypeAudio].begin();
             for (; it != tracks[kTrackTypeAudio].end(); ++it)
             {