From bcc9e32cd3c886fbe02f1b2573bd19ca9ec340dc Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Wed, 29 Oct 2025 22:19:24 +0100
Subject: Don't report channels as mapped when they are not included in the
 film's channel count.

So e.g. if you map the 7.1 surrounds but have a 6-channel film it should
consider those channels un-mapped.
---
 src/lib/film.cc           | 16 ++++++++++++----
 src/lib/film.h            |  5 +++++
 test/cpl_metadata_test.cc | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/src/lib/film.cc b/src/lib/film.cc
index c6a6f3cce..8dc55c590 100644
--- a/src/lib/film.cc
+++ b/src/lib/film.cc
@@ -797,11 +797,18 @@ list<int>
 Film::mapped_audio_channels() const
 {
 	list<int> mapped;
+	auto const highest_channel = audio_channels() - 1;
+
+	auto maybe_add = [&mapped, highest_channel](int channel) {
+		if (channel <= highest_channel) {
+			mapped.push_back(channel);
+		}
+	};
 
 	if (audio_processor()) {
 		/* Assume all a processor's declared output channels are mapped */
 		for (int i = 0; i < audio_processor()->out_channels(); ++i) {
-			mapped.push_back(i);
+			maybe_add(i);
 		}
 
 		/* Check to see if channels that the processor passes through are mapped */
@@ -810,7 +817,7 @@ Film::mapped_audio_channels() const
 			if (i->audio) {
 				for (auto c: i->audio->mapping().mapped_output_channels()) {
 					if (std::find(pass.begin(), pass.end(), dcp::Channel(c)) != pass.end()) {
-						mapped.push_back(c);
+						maybe_add(c);
 					}
 				}
 			}
@@ -819,8 +826,9 @@ Film::mapped_audio_channels() const
 	} else {
 		for (auto i: content()) {
 			if (i->audio) {
-				auto c = i->audio->mapping().mapped_output_channels();
-				copy(c.begin(), c.end(), back_inserter(mapped));
+				for (auto c: i->audio->mapping().mapped_output_channels()) {
+					maybe_add(c);
+				}
 			}
 		}
 
diff --git a/src/lib/film.h b/src/lib/film.h
index 8574c700f..6d04da9bf 100644
--- a/src/lib/film.h
+++ b/src/lib/film.h
@@ -173,6 +173,11 @@ public:
 	}
 
 	std::vector<dcpomatic::DCPTimePeriod> reels() const;
+
+	/** @return List of channel indicies that are mapped to the DCP.  This takes the
+	 *  value of audio_channels() into account, so even if a channel above audio_channels()
+	 *  is mapped it will not be returned here.
+	 */
 	std::list<int> mapped_audio_channels() const;
 
 	boost::optional<dcp::LanguageTag> audio_language() const {
diff --git a/test/cpl_metadata_test.cc b/test/cpl_metadata_test.cc
index b3c269919..b8857968d 100644
--- a/test/cpl_metadata_test.cc
+++ b/test/cpl_metadata_test.cc
@@ -119,3 +119,49 @@ BOOST_AUTO_TEST_CASE(main_sound_configuration_test_71)
 
 	BOOST_CHECK_EQUAL(msc->as_string(), "71/L,R,C,LFE,Lss,Rss,-,VIN,-,-,Lrs,Rrs");
 }
+
+
+BOOST_AUTO_TEST_CASE(main_sound_configuration_test_71_mapped_but_51_dcp)
+{
+	auto picture = content_factory("test/data/flat_red.png")[0];
+	auto L = content_factory("test/data/L.wav")[0];
+	auto R = content_factory("test/data/R.wav")[0];
+	auto C = content_factory("test/data/C.wav")[0];
+	auto Lfe = content_factory("test/data/Lfe.wav")[0];
+	auto Ls = content_factory("test/data/Ls.wav")[0];
+	auto Rs = content_factory("test/data/Rs.wav")[0];
+	auto BsL = content_factory("test/data/Ls.wav")[0];
+	auto BsR = content_factory("test/data/Rs.wav")[0];
+	auto VI = content_factory("test/data/sine_440.wav")[0];
+
+	auto film = new_test_film("main_sound_configuration_test_71_mapped_51_set_vi", { picture, L, R, C, Lfe, Ls, Rs, BsL, BsR, VI });
+	film->set_audio_channels(6);
+
+	auto set_map = [](shared_ptr<Content> content, dcp::Channel channel) {
+		auto map = content->audio->mapping();
+		map.set(0, channel, 1.0f);
+		content->audio->set_mapping(map);
+	};
+
+	set_map(L, dcp::Channel::LEFT);
+	set_map(R, dcp::Channel::RIGHT);
+	set_map(C, dcp::Channel::CENTRE);
+	set_map(Lfe, dcp::Channel::LFE);
+	set_map(Ls, dcp::Channel::LS);
+	set_map(Rs, dcp::Channel::RS);
+	set_map(BsL, dcp::Channel::BSL);
+	set_map(BsR, dcp::Channel::BSR);
+	set_map(VI, dcp::Channel::VI);
+
+	make_and_verify_dcp(film);
+
+	dcp::DCP dcp(film->dir(film->dcp_name()));
+	dcp.read();
+	BOOST_REQUIRE_EQUAL(dcp.cpls().size(), 1U);
+	auto cpl = dcp.cpls()[0];
+
+	auto msc = cpl->main_sound_configuration();
+	BOOST_REQUIRE(msc);
+
+	BOOST_CHECK_EQUAL(msc->as_string(), "51/L,R,C,LFE,Ls,Rs");
+}
-- 
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