Prevent selection of too few DCP channels (#611).

This makes Film::audio_channels() return a minimum of any active
processor's output channel count, even if fewer DCP channels have
been selected.  It may have been neater code-wise to make Player cope
if such a setting is made, but it would probably confuse people
if we don't auto-fix it (like this commit does).

2 files changed, 21 insertions, 4 deletions

diff --git a/src/lib/film.cc b/src/lib/film.cc
index d67182022..98b921029 100644
--- a/src/lib/film.cc
+++ b/src/lib/film.cc
@@ -72,6 +72,7 @@ using std::map;
 using std::vector;
 using std::setfill;
 using std::min;
+using std::max;
 using std::make_pair;
 using std::endl;
 using std::cout;
@@ -805,6 +806,7 @@ Film::set_audio_processor (AudioProcessor const * processor)
 {
 	_audio_processor = processor;
 	signal_changed (AUDIO_PROCESSOR);
+	signal_changed (AUDIO_CHANNELS);
 }
 
 void
@@ -1230,3 +1232,18 @@ Film::audio_output_names () const
 
 	return vector<string> (n.begin(), n.begin() + audio_channels ());
 }
+
+int
+Film::audio_channels () const
+{
+	int minimum = 0;
+	if (_audio_processor) {
+		minimum = _audio_processor->out_channels ();
+	}
+
+	if (minimum % 2 == 1) {
+		++minimum;
+	}
+
+	return max (minimum, _audio_channels);
+}
diff --git a/src/lib/film.h b/src/lib/film.h
index f9dc0ed9c..a1daebe78 100644
--- a/src/lib/film.h
+++ b/src/lib/film.h
@@ -223,9 +223,7 @@ public:
 		return _video_frame_rate;
 	}
 
-	int audio_channels () const {
-		return _audio_channels;
-	}
+	int audio_channels () const;
 
 	bool three_d () const {
 		return _three_d;
@@ -326,7 +324,9 @@ private:
 	int _video_frame_rate;
 	/** The date that we should use in a ISDCF name */
 	boost::gregorian::date _isdcf_date;
-	/** Number of audio channels to put in the DCP */
+	/** Number of audio channels requested for the DCP; this will be overridden
+	    if we are using an audio processor which outputs more channels.
+	*/
 	int _audio_channels;
 	/** If true, the DCP will be written in 3D mode; otherwise in 2D.
 	    This will be regardless of what content is on the playlist.