Reproduce MCA subdescriptors when writing XML without the assets being present.

This assumes that we don't read a CPL, modify the sound assets, then
write it out again.  Maybe we should make that possible (e.g. by
invalidating the CPL's MCA subdescriptors list when changing sound).

6 files changed, 251 insertions, 31 deletions

diff --git a/src/cpl.cc b/src/cpl.cc
index 2fbe373a..3e7ca7a3 100644
--- a/src/cpl.cc
+++ b/src/cpl.cc
@@ -272,6 +272,9 @@ CPL::read_composition_metadata_asset(cxml::ConstNodePtr node, vector<dcp::Verifi
 {
 	_cpl_metadata_id = remove_urn_uuid(node->string_child("Id"));
 
+	_cpl_metadata_edit_rate = dcp::Fraction(node->string_child("EditRate"));
+	_cpl_metadata_intrinsic_duration = node->number_child<int64_t>("IntrinsicDuration");
+
 	/* FullContentTitleText is compulsory but in DoM #2295 we saw a commercial tool which
 	 * apparently didn't include it, so as usual we have to be defensive.
 	 */
@@ -398,45 +401,52 @@ CPL::read_composition_metadata_asset(cxml::ConstNodePtr node, vector<dcp::Verifi
 
 	if (node->optional_node_child("MCASubDescriptors")) {
 		_profile = Profile::SMPTE_BV21;
+		for (auto descriptor: node->node_child("MCASubDescriptors")->node_children()) {
+			if (!descriptor->is_text()) {
+				_mca_sub_descriptors.push_back(MCASubDescriptor(descriptor));
+			}
+		}
 	} else {
 		_profile = Profile::SMPTE_BV20;
 	}
 }
 
 
-void
-CPL::write_mca_subdescriptors(xmlpp::Element* parent, shared_ptr<const SoundAsset> asset) const
+vector<MCASubDescriptor>
+CPL::create_mca_subdescriptors(shared_ptr<const SoundAsset> asset) const
 {
+	vector<MCASubDescriptor> descriptors;
+
 	auto reader = asset->start_read();
+
 	ASDCP::MXF::SoundfieldGroupLabelSubDescriptor* soundfield;
 	ASDCP::Result_t r = reader->reader()->OP1aHeader().GetMDObjectByType(
 		asdcp_smpte_dict->ul(ASDCP::MDD_SoundfieldGroupLabelSubDescriptor),
 		reinterpret_cast<ASDCP::MXF::InterchangeObject**>(&soundfield)
 		);
+
 	if (KM_SUCCESS(r)) {
-		auto mca_subs = cxml::add_child(parent, "mca:MCASubDescriptors");
-		mca_subs->set_namespace_declaration(mca_sub_descriptors_ns, "mca");
-		mca_subs->set_namespace_declaration(smpte_395_ns, "r0");
-		mca_subs->set_namespace_declaration(smpte_335_ns, "r1");
-		auto sf = cxml::add_child(mca_subs, "SoundfieldGroupLabelSubDescriptor", string("r0"));
+		MCASubDescriptor descriptor("SoundfieldGroupLabelSubDescriptor");
 		char buffer[64];
 		soundfield->InstanceUID.EncodeString(buffer, sizeof(buffer));
-		cxml::add_child(sf, "InstanceID", string("r1"))->add_child_text("urn:uuid:" + string(buffer));
+		descriptor.instance_id = buffer;
 		soundfield->MCALabelDictionaryID.EncodeString(buffer, sizeof(buffer));
-		cxml::add_child(sf, "MCALabelDictionaryID", string("r1"))->add_child_text("urn:smpte:ul:" + string(buffer));
+		descriptor.mca_label_dictionary_id = "urn:smpte:ul:" + string(buffer);
 		soundfield->MCALinkID.EncodeString(buffer, sizeof(buffer));
-		cxml::add_child(sf, "MCALinkID", string("r1"))->add_child_text("urn:uuid:" + string(buffer));
+		descriptor.mca_link_id = buffer;
 		soundfield->MCATagSymbol.EncodeString(buffer, sizeof(buffer));
-		cxml::add_child(sf, "MCATagSymbol", string("r1"))->add_child_text(buffer);
+		descriptor.mca_tag_symbol = buffer;
 		if (!soundfield->MCATagName.empty()) {
 			soundfield->MCATagName.get().EncodeString(buffer, sizeof(buffer));
-			cxml::add_child(sf, "MCATagName", string("r1"))->add_child_text(buffer);
+			descriptor.mca_tag_name = buffer;
 		}
 		if (!soundfield->RFC5646SpokenLanguage.empty()) {
 			soundfield->RFC5646SpokenLanguage.get().EncodeString(buffer, sizeof(buffer));
-			cxml::add_child(sf, "RFC5646SpokenLanguage", string("r1"))->add_child_text(buffer);
+			descriptor.rfc5646_spoken_language = buffer;
 		}
 
+		descriptors.push_back(descriptor);
+
 		/* Find the MCA subdescriptors in the MXF so that we can also write them here */
 		list<ASDCP::MXF::InterchangeObject*> channels;
 		auto r = reader->reader()->OP1aHeader().GetMDObjectsByType(
@@ -445,33 +455,36 @@ CPL::write_mca_subdescriptors(xmlpp::Element* parent, shared_ptr<const SoundAsse
 			);
 
 		for (auto i: channels) {
+			MCASubDescriptor descriptor("AudioChannelLabelSubDescriptor");
 			auto channel = reinterpret_cast<ASDCP::MXF::AudioChannelLabelSubDescriptor*>(i);
-			auto ch = cxml::add_child(mca_subs, "AudioChannelLabelSubDescriptor", string("r0"));
 			channel->InstanceUID.EncodeString(buffer, sizeof(buffer));
-			cxml::add_child(ch, "InstanceID", string("r1"))->add_child_text("urn:uuid:" + string(buffer));
+			descriptor.instance_id = buffer;
 			channel->MCALabelDictionaryID.EncodeString(buffer, sizeof(buffer));
-			cxml::add_child(ch, "MCALabelDictionaryID", string("r1"))->add_child_text("urn:smpte:ul:" + string(buffer));
+			descriptor.mca_label_dictionary_id = "urn:smpte:ul:" + string(buffer);
 			channel->MCALinkID.EncodeString(buffer, sizeof(buffer));
-			cxml::add_child(ch, "MCALinkID", string("r1"))->add_child_text("urn:uuid:" + string(buffer));
+			descriptor.mca_link_id = string(buffer);
 			channel->MCATagSymbol.EncodeString(buffer, sizeof(buffer));
-			cxml::add_child(ch, "MCATagSymbol", string("r1"))->add_child_text(buffer);
+			descriptor.mca_tag_symbol = buffer;
 			if (!channel->MCATagName.empty()) {
 				channel->MCATagName.get().EncodeString(buffer, sizeof(buffer));
-				cxml::add_child(ch, "MCATagName", string("r1"))->add_child_text(buffer);
+				descriptor.mca_tag_name = buffer;
 			}
 			if (!channel->MCAChannelID.empty()) {
-				cxml::add_child(ch, "MCAChannelID", string("r1"))->add_child_text(fmt::to_string(channel->MCAChannelID.get()));
+				descriptor.mca_channel_id = fmt::to_string(channel->MCAChannelID.get());
 			}
 			if (!channel->RFC5646SpokenLanguage.empty()) {
 				channel->RFC5646SpokenLanguage.get().EncodeString(buffer, sizeof(buffer));
-				cxml::add_child(ch, "RFC5646SpokenLanguage", string("r1"))->add_child_text(buffer);
+				descriptor.rfc5646_spoken_language = buffer;
 			}
 			if (!channel->SoundfieldGroupLinkID.empty()) {
 				channel->SoundfieldGroupLinkID.get().EncodeString(buffer, sizeof(buffer));
-				cxml::add_child(ch, "SoundfieldGroupLinkID", string("r1"))->add_child_text("urn:uuid:" + string(buffer));
+				descriptor.soundfield_group_link_id = buffer;
 			}
+			descriptors.push_back(descriptor);
 		}
 	}
+
+	return descriptors;
 }
 
 
@@ -488,7 +501,8 @@ CPL::maybe_write_composition_metadata_asset(xmlpp::Element* node) const
 		!_main_picture_stored_area ||
 		!_main_picture_active_area ||
 		_reels.empty() ||
-		!_reels.front()->main_picture()) {
+		(!_reels.front()->main_picture() && (!_cpl_metadata_edit_rate || !_cpl_metadata_intrinsic_duration))
+	   ) {
 		return;
 	}
 
@@ -497,9 +511,15 @@ CPL::maybe_write_composition_metadata_asset(xmlpp::Element* node) const
 
 	cxml::add_text_child(meta, "Id", "urn:uuid:" + _cpl_metadata_id);
 
-	auto mp = _reels.front()->main_picture();
-	cxml::add_text_child(meta, "EditRate", mp->edit_rate().as_string());
-	cxml::add_text_child(meta, "IntrinsicDuration", fmt::to_string(mp->intrinsic_duration()));
+	if (_cpl_metadata_edit_rate && _cpl_metadata_intrinsic_duration) {
+		/* We read these in, so reproduce them */
+		cxml::add_text_child(meta, "EditRate", _cpl_metadata_edit_rate->as_string());
+		cxml::add_text_child(meta, "IntrinsicDuration", fmt::to_string(*_cpl_metadata_intrinsic_duration));
+	} else {
+		auto mp = _reels.front()->main_picture();
+		cxml::add_text_child(meta, "EditRate", mp->edit_rate().as_string());
+		cxml::add_text_child(meta, "IntrinsicDuration", fmt::to_string(mp->intrinsic_duration()));
+	}
 
 	auto fctt = cxml::add_child(meta, "FullContentTitleText", string("meta"));
 	if (_full_content_title_text && !_full_content_title_text->empty()) {
@@ -604,10 +624,25 @@ CPL::maybe_write_composition_metadata_asset(xmlpp::Element* node) const
 		add_extension_metadata("http://www.dolby.com/schemas/2014/EDR-Metadata", "Dolby EDR", "image transfer function", *_dolby_edr_image_transfer_function);
 	}
 
-	if (_reels.front()->main_sound()) {
-		auto asset = _reels.front()->main_sound()->asset();
-		if (asset && _profile == Profile::SMPTE_BV21) {
-			write_mca_subdescriptors(meta, asset);
+	if (_profile == Profile::SMPTE_BV21) {
+		vector<MCASubDescriptor> descriptors;
+		if (!_mca_sub_descriptors.empty()) {
+			/* We read these in, so reproduce them */
+			descriptors = _mca_sub_descriptors;
+		} else if (_reels.front()->main_sound()) {
+			if (auto asset = _reels.front()->main_sound()->asset()) {
+				descriptors = create_mca_subdescriptors(asset);
+			}
+		}
+
+		if (!descriptors.empty()) {
+			auto mca_subs = cxml::add_child(meta, "mca:MCASubDescriptors");
+			mca_subs->set_namespace_declaration(mca_sub_descriptors_ns, "mca");
+			mca_subs->set_namespace_declaration(smpte_395_ns, "r0");
+			mca_subs->set_namespace_declaration(smpte_335_ns, "r1");
+			for (auto const& descriptor: descriptors) {
+				descriptor.as_xml(mca_subs);
+			}
 		}
 	}
 }
diff --git a/src/cpl.h b/src/cpl.h
index c7e41353..7bbb2d53 100644
--- a/src/cpl.h
+++ b/src/cpl.h
@@ -47,6 +47,7 @@
 #include "key.h"
 #include "language_tag.h"
 #include "main_sound_configuration.h"
+#include "mca_sub_descriptor.h"
 #include "picture_encoding.h"
 #include "profile.h"
 #include "rating.h"
@@ -367,7 +368,7 @@ private:
 
 	void maybe_write_composition_metadata_asset(xmlpp::Element* node) const;
 	void read_composition_metadata_asset(cxml::ConstNodePtr node, std::vector<dcp::VerificationNote>* notes);
-	void write_mca_subdescriptors(xmlpp::Element* parent, std::shared_ptr<const SoundAsset> asset) const;
+	std::vector<MCASubDescriptor> create_mca_subdescriptors(std::shared_ptr<const SoundAsset> asset) const;
 
 	std::string _issuer;
 	std::string _creator;
@@ -381,6 +382,8 @@ private:
 	 *  or the one read in from the existing CPL.
 	 */
 	std::string _cpl_metadata_id = make_uuid();
+	boost::optional<Fraction> _cpl_metadata_edit_rate;
+	boost::optional<int64_t> _cpl_metadata_intrinsic_duration;
 	/** Human-readable name of the composition, without any metadata (i.e. no -FTR-EN-XX- etc.) */
 	boost::optional<std::string> _full_content_title_text;
 	boost::optional<std::string> _full_content_title_text_language;
@@ -403,6 +406,7 @@ private:
 	std::vector<std::string> _additional_subtitle_languages;
 	boost::optional<std::string> _sign_language_video_language;
 	boost::optional<std::string> _dolby_edr_image_transfer_function;
+	std::vector<MCASubDescriptor> _mca_sub_descriptors;
 	bool _read_composition_metadata = false;
 
 	std::vector<std::shared_ptr<Reel>> _reels;
diff --git a/src/mca_sub_descriptor.cc b/src/mca_sub_descriptor.cc
new file mode 100644
index 00000000..34bde9f8
--- /dev/null
+++ b/src/mca_sub_descriptor.cc
@@ -0,0 +1,84 @@
+/*
+    Copyright (C) 2026 Carl Hetherington <cth@carlh.net>
+
+    This file is part of libdcp.
+
+    libdcp is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    libdcp is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with libdcp.  If not, see <http://www.gnu.org/licenses/>.
+
+    In addition, as a special exception, the copyright holders give
+    permission to link the code of portions of this program with the
+    OpenSSL library under certain conditions as described in each
+    individual source file, and distribute linked combinations
+    including the two.
+
+    You must obey the GNU General Public License in all respects
+    for all of the code used other than OpenSSL.  If you modify
+    file(s) with this exception, you may extend this exception to your
+    version of the file(s), but you are not obligated to do so.  If you
+    do not wish to do so, delete this exception statement from your
+    version.  If you delete this exception statement from all source
+    files in the program, then also delete it here.
+*/
+
+
+#include "dcp_assert.h"
+#include "mca_sub_descriptor.h"
+#include "util.h"
+LIBDCP_DISABLE_WARNINGS
+#include <libxml++/libxml++.h>
+LIBDCP_ENABLE_WARNINGS
+
+
+using std::string;
+using namespace dcp;
+
+
+MCASubDescriptor::MCASubDescriptor(cxml::ConstNodePtr node)
+{
+	tag = node->name();
+	instance_id = remove_urn_uuid(node->string_child("InstanceID"));
+	mca_label_dictionary_id = node->string_child("MCALabelDictionaryID");
+        mca_link_id = remove_urn_uuid(node->string_child("MCALinkID"));
+        mca_tag_symbol = node->string_child("MCATagSymbol");
+        mca_tag_name = node->optional_string_child("MCATagName");
+        mca_channel_id = node->optional_string_child("MCAChannelID");
+        rfc5646_spoken_language = node->optional_string_child("RFC5646SpokenLanguage");
+	if (auto id = node->optional_string_child("SoundfieldGroupLinkID")) {
+		soundfield_group_link_id = remove_urn_uuid(*id);
+	}
+}
+
+
+void
+MCASubDescriptor::as_xml(xmlpp::Element* parent) const
+{
+	auto node = cxml::add_child(parent, tag, string("r0"));
+	cxml::add_child(node, "InstanceID", string("r1"))->add_child_text("urn:uuid:" + instance_id);
+	cxml::add_child(node, "MCALabelDictionaryID", string("r1"))->add_child_text(mca_label_dictionary_id);
+	cxml::add_child(node, "MCALinkID", string("r1"))->add_child_text("urn:uuid:" + mca_link_id);
+	cxml::add_child(node, "MCATagSymbol", string("r1"))->add_child_text(mca_tag_symbol);
+	if (mca_tag_name) {
+		cxml::add_child(node, "MCATagName", string("r1"))->add_child_text(*mca_tag_name);
+	}
+	if (mca_channel_id) {
+		cxml::add_child(node, "MCAChannelID", string("r1"))->add_child_text(*mca_channel_id);
+	}
+	if (rfc5646_spoken_language) {
+		cxml::add_child(node, "RFC5646SpokenLanguage", string("r1"))->add_child_text(*rfc5646_spoken_language);
+	}
+	if (soundfield_group_link_id) {
+		cxml::add_child(node, "SoundfieldGroupLinkID", string("r1"))->add_child_text("urn:uuid:" + *soundfield_group_link_id);
+	}
+}
+
diff --git a/src/mca_sub_descriptor.h b/src/mca_sub_descriptor.h
new file mode 100644
index 00000000..4a2e8c09
--- /dev/null
+++ b/src/mca_sub_descriptor.h
@@ -0,0 +1,65 @@
+/*
+    Copyright (C) 2026 Carl Hetherington <cth@carlh.net>
+
+    This file is part of libdcp.
+
+    libdcp is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    libdcp is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with libdcp.  If not, see <http://www.gnu.org/licenses/>.
+
+    In addition, as a special exception, the copyright holders give
+    permission to link the code of portions of this program with the
+    OpenSSL library under certain conditions as described in each
+    individual source file, and distribute linked combinations
+    including the two.
+
+    You must obey the GNU General Public License in all respects
+    for all of the code used other than OpenSSL.  If you modify
+    file(s) with this exception, you may extend this exception to your
+    version of the file(s), but you are not obligated to do so.  If you
+    do not wish to do so, delete this exception statement from your
+    version.  If you delete this exception statement from all source
+    files in the program, then also delete it here.
+*/
+
+
+#include <libcxml/cxml.h>
+#include <boost/optional.hpp>
+#include <string>
+
+
+namespace dcp {
+
+
+class MCASubDescriptor
+{
+public:
+	explicit MCASubDescriptor(std::string tag_)
+		: tag(std::move(tag_))
+	{}
+	explicit MCASubDescriptor(cxml::ConstNodePtr node);
+
+	void as_xml(xmlpp::Element* node) const;
+
+	std::string tag;
+	std::string instance_id;
+	std::string mca_label_dictionary_id;
+	std::string mca_link_id;
+	std::string mca_tag_symbol;
+	boost::optional<std::string> mca_tag_name;
+	boost::optional<std::string> mca_channel_id;
+	boost::optional<std::string> rfc5646_spoken_language;
+	boost::optional<std::string> soundfield_group_link_id;
+};
+
+
+}
diff --git a/src/wscript b/src/wscript
index 4fb4c359..4df80173 100644
--- a/src/wscript
+++ b/src/wscript
@@ -75,6 +75,7 @@ def build(bld):
              local_time.cc
              locale_convert.cc
              main_sound_configuration.cc
+             mca_sub_descriptor.cc
              metadata.cc
              modified_gamma_transfer_function.cc
              mono_j2k_picture_asset.cc
@@ -189,6 +190,7 @@ def build(bld):
               local_time.h
               locale_convert.h
               main_sound_configuration.h
+              mca_sub_descriptor.h
               metadata.h
               mpeg2_picture_asset_writer.h
               modified_gamma_transfer_function.h
diff --git a/test/cpl_metadata_test.cc b/test/cpl_metadata_test.cc
index 2dc6da7d..cc86a37e 100644
--- a/test/cpl_metadata_test.cc
+++ b/test/cpl_metadata_test.cc
@@ -507,3 +507,33 @@ BOOST_AUTO_TEST_CASE(check_dolby_edr_metadata)
 	BOOST_CHECK_EQUAL(check.dolby_edr_image_transfer_function().get_value_or(""), "PQ10K");
 }
 
+
+BOOST_AUTO_TEST_CASE(cpl_metadata_passthrough)
+{
+	boost::filesystem::path tmp = "build/test/ak";
+	dcp::filesystem::remove_all(tmp);
+
+	/* Plain dcp::filesystem::copy does not seem work on Ubuntu 16.04 */
+	dcp::filesystem::create_directory(tmp);
+	for (auto file: boost::filesystem::directory_iterator(private_test / "ak")) {
+		dcp::filesystem::copy_file(file, tmp / file.path().filename());
+	}
+
+	dcp::DCP dcp("build/test/ak");
+	dcp.read();
+
+	auto signer = make_shared<dcp::CertificateChain>();
+	signer->add(dcp::Certificate(dcp::file_to_string("test/ref/crypt/ca.self-signed.pem")));
+	signer->add(dcp::Certificate(dcp::file_to_string("test/ref/crypt/intermediate.signed.pem")));
+	signer->add(dcp::Certificate(dcp::file_to_string("test/ref/crypt/leaf.signed.pem")));
+	signer->set_key(dcp::file_to_string("test/ref/crypt/leaf.key"));
+
+	dcp.write_xml(signer);
+
+	check_xml(
+		dcp::file_to_string(private_test / "ak" / "cpl_48b6b1d3-37fd-4782-8ad1-f883e5020d47.xml"),
+		dcp::file_to_string(boost::filesystem::path("build/test/ak") / "cpl_48b6b1d3-37fd-4782-8ad1-f883e5020d47.xml"),
+		{"Signer", "Signature"}
+	);
+}
+