Fix race between the Butler thread starting and audio (perhaps) being disabled.

This could cause Butler::audio to be called with _audio_channels = 0
and _disable_audio = false, causing an exception in AudioBuffers when
remap() tried to make an AudioBuffers object with a channel count of 0.

3 files changed, 21 insertions, 14 deletions

diff --git a/src/lib/butler.cc b/src/lib/butler.cc
index 27b39ba4f..ce35b1f39 100644
--- a/src/lib/butler.cc
+++ b/src/lib/butler.cc
@@ -69,7 +69,8 @@ Butler::Butler (
 	VideoRange video_range,
 	Image::Alignment alignment,
 	bool fast,
-	bool prepare_only_proxy
+	bool prepare_only_proxy,
+	Audio audio
 	)
 	: _film (film)
 	, _player (player)
@@ -81,7 +82,7 @@ Butler::Butler (
 	, _stop_thread (false)
 	, _audio_mapping (audio_mapping)
 	, _audio_channels (audio_channels)
-	, _disable_audio (false)
+	, _disable_audio (audio == Audio::DISABLED)
 	, _pixel_format (pixel_format)
 	, _video_range (video_range)
 	, _alignment (alignment)
@@ -394,14 +395,6 @@ Butler::get_audio (Behaviour behaviour, float* out, Frame frames)
 }
 
 
-void
-Butler::disable_audio ()
-{
-	boost::mutex::scoped_lock lm (_mutex);
-	_disable_audio = true;
-}
-
-
 pair<size_t, string>
 Butler::memory_used () const
 {
diff --git a/src/lib/butler.h b/src/lib/butler.h
index c7e71658d..79701d370 100644
--- a/src/lib/butler.h
+++ b/src/lib/butler.h
@@ -38,6 +38,12 @@ class PlayerVideo;
 class Butler : public ExceptionStore
 {
 public:
+	enum class Audio
+	{
+		ENABLED,
+		DISABLED
+	};
+
 	Butler (
 		std::weak_ptr<const Film> film,
 		std::shared_ptr<Player> player,
@@ -47,7 +53,8 @@ public:
 		VideoRange video_range,
 		Image::Alignment alignment,
 		bool fast,
-		bool prepare_only_proxy
+		bool prepare_only_proxy,
+		Audio audio
 		);
 
 	~Butler ();
@@ -81,8 +88,6 @@ public:
 	boost::optional<dcpomatic::DCPTime> get_audio (Behaviour behaviour, float* out, Frame frames);
 	boost::optional<TextRingBuffers::Data> get_closed_caption ();
 
-	void disable_audio ();
-
 	std::pair<size_t, std::string> memory_used () const;
 
 private:
diff --git a/src/lib/ffmpeg_encoder.cc b/src/lib/ffmpeg_encoder.cc
index d4f0b4b47..bcf2b82de 100644
--- a/src/lib/ffmpeg_encoder.cc
+++ b/src/lib/ffmpeg_encoder.cc
@@ -108,7 +108,16 @@ FFmpegEncoder::FFmpegEncoder (
 	}
 
 	_butler = std::make_shared<Butler>(
-		_film, _player, map, _output_audio_channels, bind(&PlayerVideo::force, FFmpegFileEncoder::pixel_format(format)), VideoRange::VIDEO, Image::Alignment::PADDED, false, false
+		_film,
+		_player,
+		map,
+		_output_audio_channels,
+		bind(&PlayerVideo::force, FFmpegFileEncoder::pixel_format(format)),
+		VideoRange::VIDEO,
+		Image::Alignment::PADDED,
+		false,
+		false,
+		Butler::Audio::ENABLED
 		);
 }