Write MCA tags based on the specified sound field.

I had previously assumed that one should write MCA information into
the sound MXF based on what channels actually contain sound rather
than silence.

However a previous example of a stereo DCP gives a verification error
in EasyDCP (see DoM bug #1935) which is solved by adding MCA tags
for each channel in the specified sound field (e.g. at least 6 tags
for a file which is marked as 5.1) even if the audio is really stereo.

This commit removes the "active channels" stuff and makes sure
that if we say a file is 5.1 we write at least 6 MCA tags (and
similarly for 7.1).

5 files changed, 37 insertions, 29 deletions

diff --git a/src/sound_asset.cc b/src/sound_asset.cc
index 1c0a181f..fe0c5dd0 100644
--- a/src/sound_asset.cc
+++ b/src/sound_asset.cc
@@ -222,13 +222,13 @@ SoundAsset::equals (shared_ptr<const Asset> other, EqualityOptions opt, NoteHand
 
 
 shared_ptr<SoundAssetWriter>
-SoundAsset::start_write (boost::filesystem::path file, vector<Channel> active_channels, bool atmos_sync)
+SoundAsset::start_write (boost::filesystem::path file, bool atmos_sync)
 {
 	if (atmos_sync && _channels < 14) {
 		throw MiscError ("Insufficient channels to write ATMOS sync (there must be at least 14)");
 	}
 
-	return shared_ptr<SoundAssetWriter> (new SoundAssetWriter(this, file, active_channels, atmos_sync));
+	return shared_ptr<SoundAssetWriter> (new SoundAssetWriter(this, file, atmos_sync));
 }
 
 
diff --git a/src/sound_asset.h b/src/sound_asset.h
index e238de46..e58773e4 100644
--- a/src/sound_asset.h
+++ b/src/sound_asset.h
@@ -75,7 +75,7 @@ public:
 	explicit SoundAsset (boost::filesystem::path file);
 	SoundAsset (Fraction edit_rate, int sampling_rate, int channels, LanguageTag language, Standard standard);
 
-	std::shared_ptr<SoundAssetWriter> start_write (boost::filesystem::path file, std::vector<Channel> active_channels, bool atmos_sync = false);
+	std::shared_ptr<SoundAssetWriter> start_write (boost::filesystem::path file, bool atmos_sync = false);
 	std::shared_ptr<SoundAssetReader> start_read () const;
 
 	bool equals (
diff --git a/src/sound_asset_writer.cc b/src/sound_asset_writer.cc
index c0cdf0cb..205a45ab 100644
--- a/src/sound_asset_writer.cc
+++ b/src/sound_asset_writer.cc
@@ -66,12 +66,11 @@ struct SoundAssetWriter::ASDCPState
 };
 
 
-SoundAssetWriter::SoundAssetWriter (SoundAsset* asset, boost::filesystem::path file, vector<Channel> active_channels, bool sync)
+SoundAssetWriter::SoundAssetWriter (SoundAsset* asset, boost::filesystem::path file, bool sync)
 	: AssetWriter (asset, file)
 	, _state (new SoundAssetWriter::ASDCPState)
 	, _asset (asset)
 	, _sync (sync)
-	, _active_channels (active_channels)
 {
 	DCP_ASSERT (!_sync || _asset->channels() >= 14);
 	DCP_ASSERT (!_sync || _asset->standard() == Standard::SMPTE);
@@ -117,7 +116,7 @@ SoundAssetWriter::start ()
 		boost::throw_exception (FileError("could not open audio MXF for writing", _file.string(), r));
 	}
 
-	if (_asset->standard() == Standard::SMPTE && !_active_channels.empty()) {
+	if (_asset->standard() == Standard::SMPTE) {
 
 		ASDCP::MXF::WaveAudioDescriptor* essence_descriptor = nullptr;
 		_state->mxf_writer.OP1aHeader().GetMDObjectByType(
@@ -145,15 +144,26 @@ SoundAssetWriter::start ()
 		_state->mxf_writer.OP1aHeader().AddChildObject(soundfield);
 		essence_descriptor->SubDescriptors.push_back(soundfield->InstanceUID);
 
-		for (auto i: _active_channels) {
+		/* We must describe at least the number of channels in `field', even if they aren't
+		 * in the asset (I think)
+		 */
+		int descriptors = max(_asset->channels(), field == MCASoundField::FIVE_POINT_ONE ? 6 : 8);
+
+		auto const used = used_audio_channels();
+
+		for (auto i = 0; i < descriptors; ++i) {
+			auto dcp_channel = static_cast<dcp::Channel>(i);
+			if (find(used.begin(), used.end(), dcp_channel) == used.end()) {
+				continue;
+			}
 			auto channel = new ASDCP::MXF::AudioChannelLabelSubDescriptor(asdcp_smpte_dict);
 			GenRandomValue (channel->MCALinkID);
 			channel->SoundfieldGroupLinkID = soundfield->MCALinkID;
-			channel->MCAChannelID = static_cast<int>(i) + 1;
-			channel->MCATagSymbol = "ch" + channel_to_mca_id(i, field);
-			channel->MCATagName = channel_to_mca_name(i, field);
+			channel->MCAChannelID = i + 1;
+			channel->MCATagSymbol = "ch" + channel_to_mca_id(dcp_channel, field);
+			channel->MCATagName = channel_to_mca_name(dcp_channel, field);
 			channel->RFC5646SpokenLanguage = _asset->language();
-			channel->MCALabelDictionaryID = channel_to_mca_universal_label(i, field, asdcp_smpte_dict);
+			channel->MCALabelDictionaryID = channel_to_mca_universal_label(dcp_channel, field, asdcp_smpte_dict);
 			_state->mxf_writer.OP1aHeader().AddChildObject(channel);
 			essence_descriptor->SubDescriptors.push_back(channel->InstanceUID);
 		}
diff --git a/src/sound_asset_writer.h b/src/sound_asset_writer.h
index d2eba024..b024749f 100644
--- a/src/sound_asset_writer.h
+++ b/src/sound_asset_writer.h
@@ -78,7 +78,7 @@ private:
 	friend class SoundAsset;
 	friend struct ::sync_test1;
 
-	SoundAssetWriter (SoundAsset *, boost::filesystem::path, std::vector<Channel> active_channels, bool sync);
+	SoundAssetWriter (SoundAsset *, boost::filesystem::path, bool sync);
 
 	void start ();
 	void write_current_frame ();
@@ -99,8 +99,6 @@ private:
 	/** index of the sync packet (0-3) which starts the next edit unit */
 	int _sync_packet = 0;
 	FSK _fsk;
-
-	std::vector<Channel> _active_channels;
 };
 
 }
diff --git a/src/types.cc b/src/types.cc
index b4c10ddc..44422ca9 100644
--- a/src/types.cc
+++ b/src/types.cc
@@ -827,20 +827,20 @@ dcp::channel_to_mca_universal_label (Channel c, MCASoundField field, ASDCP::Dict
 vector<dcp::Channel>
 dcp::used_audio_channels ()
 {
-	vector<Channel> c;
-	c.push_back (Channel::LEFT);
-	c.push_back (Channel::RIGHT);
-	c.push_back (Channel::CENTRE);
-	c.push_back (Channel::LFE);
-	c.push_back (Channel::LS);
-	c.push_back (Channel::RS);
-	c.push_back (Channel::HI);
-	c.push_back (Channel::VI);
-	c.push_back (Channel::BSL);
-	c.push_back (Channel::BSR);
-	c.push_back (Channel::MOTION_DATA);
-	c.push_back (Channel::SYNC_SIGNAL);
-	c.push_back (Channel::SIGN_LANGUAGE);
-	return c;
+	return {
+		Channel::LEFT,
+		Channel::RIGHT,
+		Channel::CENTRE,
+		Channel::LFE,
+		Channel::LS,
+		Channel::RS,
+		Channel::HI,
+		Channel::VI,
+		Channel::BSL,
+		Channel::BSR,
+		Channel::MOTION_DATA,
+		Channel::SYNC_SIGNAL,
+		Channel::SIGN_LANGUAGE
+	};
 }