Read/write subtitle variable Z.v1.10.16

19 files changed, 373 insertions, 19 deletions

diff --git a/src/text.cc b/src/text.cc
index 158af38c..8f72b953 100644
--- a/src/text.cc
+++ b/src/text.cc
@@ -44,6 +44,9 @@
 
 
 using std::shared_ptr;
+using std::string;
+using std::vector;
+using boost::optional;
 using namespace dcp;
 
 
@@ -56,6 +59,7 @@ Text::Text(
 	float v_position,
 	VAlign v_align,
 	float z_position,
+	vector<VariableZPosition> variable_z_positions,
 	Time fade_up_time,
 	Time fade_down_time
 	)
@@ -66,6 +70,7 @@ Text::Text(
 	, _v_position (v_position)
 	, _v_align (v_align)
 	, _z_position(z_position)
+	, _variable_z_positions(variable_z_positions)
 	, _fade_up_time (fade_up_time)
 	, _fade_down_time (fade_down_time)
 {
@@ -117,6 +122,11 @@ Text::equals(shared_ptr<const Text> other, EqualityOptions const& options, NoteH
 		same = false;
 	}
 
+	if (variable_z_positions() != other->variable_z_positions()) {
+		note(NoteType::ERROR, "text variable Z positions differ");
+		same = false;
+	}
+
 	if (fade_up_time() != other->fade_up_time()) {
 		note(NoteType::ERROR, "text fade-up times differ");
 		same = false;
@@ -129,3 +139,10 @@ Text::equals(shared_ptr<const Text> other, EqualityOptions const& options, NoteH
 
 	return same;
 }
+
+
+bool dcp::operator==(Text::VariableZPosition a, Text::VariableZPosition b)
+{
+	return a.position == b.position && a.duration == b.duration;
+}
+
diff --git a/src/text.h b/src/text.h
index 70dfa3a6..f3b6ecea 100644
--- a/src/text.h
+++ b/src/text.h
@@ -97,6 +97,10 @@ public:
 		int64_t duration;
 	};
 
+	std::vector<VariableZPosition> variable_z_positions() const {
+		return _variable_z_positions;
+	}
+
 	Time fade_up_time () const {
 		return _fade_up_time;
 	}
@@ -128,6 +132,10 @@ public:
 		_z_position = z;
 	}
 
+	void set_variable_z_positions(std::vector<VariableZPosition> z) {
+		_variable_z_positions = std::move(z);
+	}
+
 	void set_fade_up_time (Time t) {
 		_fade_up_time = t;
 	}
@@ -148,6 +156,7 @@ protected:
 		float v_position,
 		VAlign v_align,
 		float z_position,
+		std::vector<VariableZPosition> variable_z,
 		Time fade_up_time,
 		Time fade_down_time
 		);
@@ -165,11 +174,15 @@ protected:
 	float _v_position = 0;
 	VAlign _v_align = VAlign::CENTER;
 	float _z_position = 0;
+	std::vector<VariableZPosition> _variable_z_positions;
 	Time _fade_up_time;
 	Time _fade_down_time;
 };
 
 
+bool operator==(Text::VariableZPosition a, Text::VariableZPosition b);
+
+
 }
 
 
diff --git a/src/text_asset.cc b/src/text_asset.cc
index c3341452..41690d93 100644
--- a/src/text_asset.cc
+++ b/src/text_asset.cc
@@ -206,6 +206,10 @@ TextAsset::position_align(TextAsset::ParseState& ps, xmlpp::Element const * node
 	if (auto zp = optional_number_attribute<float>(node, "Zposition")) {
 		ps.z_position = zp.get() / 100;
 	}
+
+	if (auto variable_z = optional_string_attribute(node, "VariableZ")) {
+		ps.variable_z = *variable_z;
+	}
 }
 
 
@@ -248,6 +252,14 @@ TextAsset::subtitle_node_state(xmlpp::Element const * node, optional<int> tcr) c
 	ps.out = Time (string_attribute(node, "TimeOut"), tcr);
 	ps.fade_up_time = fade_time (node, "FadeUpTime", tcr);
 	ps.fade_down_time = fade_time (node, "FadeDownTime", tcr);
+
+	for (auto child: node->get_children()) {
+		auto element = dynamic_cast<xmlpp::Element const*>(child);
+		if (element && element->get_name() == "LoadVariableZ") {
+			ps.load_variable_z.push_back(LoadVariableZ(element));
+		}
+	}
+
 	return ps;
 }
 
@@ -287,6 +299,8 @@ TextAsset::parse_texts(xmlpp::Element const * node, vector<ParseState>& state, o
 		state.push_back (ParseState ());
 	} else if (node->get_name() == "Image") {
 		state.push_back (image_node_state (node));
+	} else if (node->get_name() == "LoadVariableZ") {
+		return;
 	} else {
 		throw XMLError ("unexpected node " + node->get_name());
 	}
@@ -453,6 +467,9 @@ TextAsset::maybe_add_text(
 		if (i.z_position) {
 			ps.z_position = i.z_position.get();
 		}
+		if (i.variable_z) {
+			ps.variable_z = i.variable_z.get();
+		}
 		if (i.direction) {
 			ps.direction = i.direction.get();
 		}
@@ -471,6 +488,13 @@ TextAsset::maybe_add_text(
 		if (i.type) {
 			ps.type = i.type.get();
 		}
+		for (auto j: i.load_variable_z) {
+			/* j is a LoadVariableZ from this "sub" ParseState. See if we should add it to the end result */
+			auto const k = std::find_if(ps.load_variable_z.begin(), ps.load_variable_z.end(), [j](LoadVariableZ const& z) { return j.id() == z.id(); });
+			if (k == ps.load_variable_z.end()) {
+				ps.load_variable_z.push_back(j);
+			}
+		}
 	}
 
 	if (!ps.in || !ps.out) {
@@ -482,6 +506,12 @@ TextAsset::maybe_add_text(
 
 	switch (ps.type.get()) {
 	case ParseState::Type::TEXT:
+	{
+		vector<Text::VariableZPosition> variable_z;
+		auto iter = std::find_if(ps.load_variable_z.begin(), ps.load_variable_z.end(), [&ps](LoadVariableZ const& z) { return z.id() == ps.variable_z; });
+		if (iter != ps.load_variable_z.end()) {
+			variable_z = iter->positions();
+		}
 		_texts.push_back (
 			make_shared<TextString>(
 				ps.font_id,
@@ -498,6 +528,7 @@ TextAsset::maybe_add_text(
 				ps.v_position.get_value_or(0),
 				ps.v_align.get_value_or(VAlign::CENTER),
 				ps.z_position.get_value_or(0),
+				variable_z,
 				ps.direction.get_value_or (Direction::LTR),
 				text,
 				ps.effect.get_value_or (Effect::NONE),
@@ -509,6 +540,7 @@ TextAsset::maybe_add_text(
 				)
 			);
 		break;
+	}
 	case ParseState::Type::IMAGE:
 	{
 		switch (standard) {
@@ -530,6 +562,12 @@ TextAsset::maybe_add_text(
 			break;
 		}
 
+		vector<Text::VariableZPosition> variable_z;
+		auto iter = std::find_if(ps.load_variable_z.begin(), ps.load_variable_z.end(), [&ps](LoadVariableZ const& z) { return ps.variable_z && z.id() == *ps.variable_z; });
+		if (iter != ps.load_variable_z.end()) {
+			variable_z = iter->positions();
+		}
+
 		/* Add a text with no image data and we'll fill that in later */
 		_texts.push_back(
 			make_shared<TextImage>(
@@ -542,6 +580,7 @@ TextAsset::maybe_add_text(
 				ps.v_position.get_value_or(0),
 				ps.v_align.get_value_or(VAlign::CENTER),
 				ps.z_position.get_value_or(0),
+				variable_z,
 				ps.fade_up_time.get_value_or(Time()),
 				ps.fade_down_time.get_value_or(Time())
 				)
@@ -747,6 +786,7 @@ TextAsset::texts_as_xml(xmlpp::Element* xml_root, int time_code_rate, Standard s
 	float last_v_position;
 	float last_z_position;
 	Direction last_direction;
+	int load_variable_z_index = 1;
 
 	for (auto i: sorted) {
 		if (!subtitle ||
@@ -783,6 +823,7 @@ TextAsset::texts_as_xml(xmlpp::Element* xml_root, int time_code_rate, Standard s
 					is->v_align(),
 					is->v_position(),
 					is->z_position(),
+					subtitle->find_or_add_variable_z_positions(is->variable_z_positions(), load_variable_z_index),
 					is->direction(),
 					is->rubies()
 					);
@@ -802,7 +843,16 @@ TextAsset::texts_as_xml(xmlpp::Element* xml_root, int time_code_rate, Standard s
 		if (auto ii = dynamic_pointer_cast<TextImage>(i)) {
 			text.reset ();
 			subtitle->children.push_back (
-				make_shared<order::Image>(subtitle, ii->id(), ii->png_image(), ii->h_align(), ii->h_position(), ii->v_align(), ii->v_position(), ii->z_position())
+				make_shared<order::Image>(
+					subtitle, ii->id(),
+					ii->png_image(),
+					ii->h_align(),
+					ii->h_position(),
+					ii->v_align(),
+					ii->v_position(),
+					ii->z_position(),
+					subtitle->find_or_add_variable_z_positions(ii->variable_z_positions(), load_variable_z_index)
+					)
 				);
 		}
 	}
diff --git a/src/text_asset.h b/src/text_asset.h
index 4d739027..113896f8 100644
--- a/src/text_asset.h
+++ b/src/text_asset.h
@@ -44,6 +44,7 @@
 #include "array_data.h"
 #include "asset.h"
 #include "dcp_time.h"
+#include "load_variable_z.h"
 #include "subtitle_standard.h"
 #include "text_string.h"
 #include <libcxml/cxml.h>
@@ -156,6 +157,7 @@ protected:
 		boost::optional<float> v_position;
 		boost::optional<VAlign> v_align;
 		boost::optional<float> z_position;
+		boost::optional<std::string> variable_z;
 		boost::optional<Direction> direction;
 		boost::optional<Time> in;
 		boost::optional<Time> out;
@@ -167,6 +169,8 @@ protected:
 		};
 		boost::optional<Type> type;
 		float space_before = 0;
+
+		std::vector<LoadVariableZ> load_variable_z;
 	};
 
 	void parse_texts(xmlpp::Element const * node, std::vector<ParseState>& state, boost::optional<int> tcr, Standard standard);
@@ -181,6 +185,7 @@ protected:
 
 	/** All our texts, in no particular order */
 	std::vector<std::shared_ptr<Text>> _texts;
+	std::vector<LoadVariableZ> _load_variable_z;
 
 	class Font
 	{
diff --git a/src/text_asset_internal.cc b/src/text_asset_internal.cc
index 549bbec9..4ae5dbfe 100644
--- a/src/text_asset_internal.cc
+++ b/src/text_asset_internal.cc
@@ -44,9 +44,12 @@
 #include <cmath>
 
 
+using std::dynamic_pointer_cast;
 using std::string;
 using std::map;
 using std::shared_ptr;
+using std::vector;
+using boost::optional;
 using namespace dcp;
 
 
@@ -166,7 +169,16 @@ order::Part::write_xml (xmlpp::Element* parent, order::Context& context) const
 
 
 static void
-position_align (xmlpp::Element* e, order::Context& context, HAlign h_align, float h_position, VAlign v_align, float v_position, float z_position)
+position_align(
+		xmlpp::Element* e,
+		order::Context& context,
+		HAlign h_align,
+		float h_position,
+		VAlign v_align,
+		float v_position,
+		float z_position,
+		optional<string> variable_z
+		)
 {
 	if (h_align != HAlign::CENTER) {
 		if (context.standard == Standard::SMPTE) {
@@ -207,6 +219,10 @@ position_align (xmlpp::Element* e, order::Context& context, HAlign h_align, floa
 	if (fabs(z_position) > ALIGN_EPSILON && context.standard == Standard::SMPTE) {
 		e->set_attribute("Zposition", fmt::format("{:.6}", z_position * 100));
 	}
+
+	if (variable_z) {
+		e->set_attribute("VariableZ", *variable_z);
+	}
 }
 
 
@@ -215,7 +231,7 @@ order::Text::as_xml (xmlpp::Element* parent, Context& context) const
 {
 	auto e = cxml::add_child(parent, "Text");
 
-	position_align(e, context, _h_align, _h_position, _v_align, _v_position, _z_position);
+	position_align(e, context, _h_align, _h_position, _v_align, _v_position, _z_position, _variable_z);
 
 	/* Interop only supports "horizontal" or "vertical" for direction, so only write this
 	   for SMPTE.
@@ -240,6 +256,24 @@ order::Text::as_xml (xmlpp::Element* parent, Context& context) const
 }
 
 
+optional<string>
+order::Subtitle::find_or_add_variable_z_positions(vector<dcp::Text::VariableZPosition> const& positions, int& load_variable_z_index)
+{
+	if (positions.empty()) {
+		return {};
+	}
+
+	auto iter = std::find_if(_load_variable_z.begin(), _load_variable_z.end(), [positions](LoadVariableZ const& load) { return positions == load.positions(); });
+	if (iter == _load_variable_z.end()) {
+		auto const id = fmt::format("Zvector{}", load_variable_z_index++);
+		_load_variable_z.push_back(LoadVariableZ(id, positions));
+		return id;
+	}
+
+	return iter->id();
+}
+
+
 xmlpp::Element*
 order::Subtitle::as_xml (xmlpp::Element* parent, Context& context) const
 {
@@ -254,6 +288,11 @@ order::Subtitle::as_xml (xmlpp::Element* parent, Context& context) const
 		e->set_attribute("FadeUpTime", fmt::to_string(_fade_up.as_editable_units_ceil(context.time_code_rate)));
 		e->set_attribute("FadeDownTime", fmt::to_string(_fade_down.as_editable_units_ceil(context.time_code_rate)));
 	}
+
+	for (auto const& vz: _load_variable_z) {
+		vz.as_xml(cxml::add_child(e, "LoadVariableZ"));
+	}
+
 	return e;
 }
 
@@ -277,7 +316,7 @@ order::Image::as_xml (xmlpp::Element* parent, Context& context) const
 {
 	auto e = cxml::add_child(parent, "Image");
 
-	position_align(e, context, _h_align, _h_position, _v_align, _v_position, _z_position);
+	position_align(e, context, _h_align, _h_position, _v_align, _v_position, _z_position, _variable_z);
 	if (context.standard == Standard::SMPTE) {
 		e->add_child_text ("urn:uuid:" + _id);
 	} else {
@@ -286,3 +325,4 @@ order::Image::as_xml (xmlpp::Element* parent, Context& context) const
 
 	return e;
 }
+
diff --git a/src/text_asset_internal.h b/src/text_asset_internal.h
index ddbc8833..2dfccce9 100644
--- a/src/text_asset_internal.h
+++ b/src/text_asset_internal.h
@@ -44,6 +44,7 @@
 #include "array_data.h"
 #include "dcp_time.h"
 #include "h_align.h"
+#include "load_variable_z.h"
 #include "raw_convert.h"
 #include "v_align.h"
 #include "warnings.h"
@@ -146,25 +147,41 @@ private:
 class Text : public Part
 {
 public:
-	Text(std::shared_ptr<Part> parent, HAlign h_align, float h_position, VAlign v_align, float v_position, float z_position, Direction direction, std::vector<Ruby> rubies)
+	Text(
+			std::shared_ptr<Part> parent,
+			HAlign h_align,
+			float h_position,
+			VAlign v_align,
+			float v_position,
+			float z_position,
+			boost::optional<std::string> variable_z,
+			Direction direction,
+			std::vector<Ruby> rubies
+		)
 		: Part (parent)
 		, _h_align (h_align)
 		, _h_position (h_position)
 		, _v_align (v_align)
 		, _v_position (v_position)
 		, _z_position(z_position)
+		, _variable_z(variable_z)
 		, _direction (direction)
 		, _rubies(rubies)
 	{}
 
 	xmlpp::Element* as_xml (xmlpp::Element* parent, Context& context) const override;
 
+	boost::optional<std::string> variable_z() {
+		return _variable_z;
+	}
+
 private:
 	HAlign _h_align;
 	float _h_position;
 	VAlign _v_align;
 	float _v_position;
 	float _z_position;
+	boost::optional<std::string> _variable_z;
 	Direction _direction;
 	std::vector<Ruby> _rubies;
 };
@@ -181,6 +198,8 @@ public:
 		, _fade_down (fade_down)
 	{}
 
+	boost::optional<std::string> find_or_add_variable_z_positions(std::vector<dcp::Text::VariableZPosition> const& positions, int& load_variable_z_index);
+
 	xmlpp::Element* as_xml (xmlpp::Element* parent, Context& context) const override;
 
 private:
@@ -188,13 +207,24 @@ private:
 	Time _out;
 	Time _fade_up;
 	Time _fade_down;
+	std::vector<LoadVariableZ> _load_variable_z;
 };
 
 
 class Image : public Part
 {
 public:
-	Image (std::shared_ptr<Part> parent, std::string id, ArrayData png_data, HAlign h_align, float h_position, VAlign v_align, float v_position, float z_position)
+	Image(
+		std::shared_ptr<Part> parent,
+		std::string id,
+		ArrayData png_data,
+		HAlign h_align,
+		float h_position,
+		VAlign v_align,
+		float v_position,
+		float z_position,
+		boost::optional<std::string> variable_z
+	     )
 		: Part (parent)
 		, _png_data (png_data)
 		, _id (id)
@@ -203,6 +233,7 @@ public:
 		, _v_align (v_align)
 		, _v_position (v_position)
 		, _z_position(z_position)
+		, _variable_z(variable_z)
 	{}
 
 	xmlpp::Element* as_xml (xmlpp::Element* parent, Context& context) const override;
@@ -215,6 +246,7 @@ private:
 	VAlign _v_align;
 	float _v_position;
 	float _z_position;
+	boost::optional<std::string> _variable_z;
 };
 
 
diff --git a/src/text_image.cc b/src/text_image.cc
index 7a6c4222..119a6301 100644
--- a/src/text_image.cc
+++ b/src/text_image.cc
@@ -47,6 +47,8 @@ using std::dynamic_pointer_cast;
 using std::ostream;
 using std::shared_ptr;
 using std::string;
+using std::vector;
+using boost::optional;
 using namespace dcp;
 
 
@@ -59,10 +61,11 @@ TextImage::TextImage(
 	float v_position,
 	VAlign v_align,
 	float z_position,
+	vector<VariableZPosition> variable_z_positions,
 	Time fade_up_time,
 	Time fade_down_time
 	)
-	: Text(in, out, h_position, h_align, v_position, v_align, z_position, fade_up_time, fade_down_time)
+	: Text(in, out, h_position, h_align, v_position, v_align, z_position, variable_z_positions, fade_up_time, fade_down_time)
 	, _png_image (png_image)
 	, _id (make_uuid ())
 {
@@ -80,10 +83,11 @@ TextImage::TextImage(
 	float v_position,
 	VAlign v_align,
 	float z_position,
+	vector<VariableZPosition> variable_z_positions,
 	Time fade_up_time,
 	Time fade_down_time
 	)
-	: Text(in, out, h_position, h_align, v_position, v_align, z_position, fade_up_time, fade_down_time)
+	: Text(in, out, h_position, h_align, v_position, v_align, z_position, variable_z_positions, fade_up_time, fade_down_time)
 	, _png_image (png_image)
 	, _id (id)
 {
diff --git a/src/text_image.h b/src/text_image.h
index 1f1e464e..5b78f380 100644
--- a/src/text_image.h
+++ b/src/text_image.h
@@ -66,6 +66,7 @@ public:
 		float v_position,
 		VAlign v_align,
 		float z_position,
+		std::vector<VariableZPosition> variable_z_positions,
 		Time fade_up_time,
 		Time fade_down_time
 		);
@@ -80,6 +81,7 @@ public:
 		float v_position,
 		VAlign v_align,
 		float z_position,
+		std::vector<VariableZPosition> variable_z_positions,
 		Time fade_up_time,
 		Time fade_down_time
 		);
diff --git a/src/text_string.cc b/src/text_string.cc
index 32f9e4ed..12e86fce 100644
--- a/src/text_string.cc
+++ b/src/text_string.cc
@@ -69,6 +69,7 @@ TextString::TextString(
 	float v_position,
 	VAlign v_align,
 	float z_position,
+	vector<VariableZPosition> variable_z_positions,
 	Direction direction,
 	string text,
 	Effect effect,
@@ -78,7 +79,7 @@ TextString::TextString(
 	float space_before,
 	vector<Ruby> rubies
 	)
-	: Text(in, out, h_position, h_align, v_position, v_align, z_position, fade_up_time, fade_down_time)
+	: Text(in, out, h_position, h_align, v_position, v_align, z_position, variable_z_positions, fade_up_time, fade_down_time)
 	, _font (font)
 	, _italic (italic)
 	, _bold (bold)
@@ -127,6 +128,7 @@ dcp::operator==(TextString const & a, TextString const & b)
 		a.v_position() == b.v_position() &&
 		a.v_align() == b.v_align() &&
 		a.z_position() == b.z_position() &&
+		a.variable_z_positions() == b.variable_z_positions() &&
 		a.direction() == b.direction() &&
 		a.text() == b.text() &&
 		a.effect() == b.effect() &&
@@ -173,8 +175,8 @@ dcp::operator<<(ostream& s, TextString const & sub)
 	  << ", colour (" << sub.colour().r << ", " << sub.colour().g << ", " << sub.colour().b << ")"
 	  << ", vpos " << sub.v_position() << ", valign " << ((int) sub.v_align())
 	  << ", hpos " << sub.h_position() << ", halign " << ((int) sub.h_align())
-	  << ", zpos " << sub.z_position()
-	  << ", direction " << ((int) sub.direction())
+	  << ", zpos " << sub.z_position();
+	s << ", direction " << ((int) sub.direction())
 	  << ", effect " << ((int) sub.effect())
 	  << ", effect colour (" << sub.effect_colour().r << ", " << sub.effect_colour().g << ", " << sub.effect_colour().b << ")"
 	  << ", space before " << sub.space_before();
diff --git a/src/text_string.h b/src/text_string.h
index f532bafe..78788786 100644
--- a/src/text_string.h
+++ b/src/text_string.h
@@ -72,6 +72,7 @@ public:
 	 *  @param v_align Vertical alignment point
 	 *  @param z_position Z position as a proportion of the primary picture width between -1 and +1;
 	 *  +ve moves the image away from the viewer, -ve moves it toward the viewer, 0 is in the plane of the screen.
+	 *  @param variable_z_positions List of variable Z positions for this text (or empty).
 	 *  @param direction Direction of text
 	 *  @param text The text to display
 	 *  @param effect Effect to use
@@ -95,6 +96,7 @@ public:
 		float v_position,
 		VAlign v_align,
 		float z_position,
+		std::vector<VariableZPosition> variable_z_positions,
 		Direction direction,
 		std::string text,
 		Effect effect,
diff --git a/test/data/subtitles_with_vZani.xml b/test/data/subtitles_with_vZani.xml
new file mode 100644
index 00000000..32f08c6a
--- /dev/null
+++ b/test/data/subtitles_with_vZani.xml
@@ -0,0 +1,61 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<SubtitleReel xmlns="http://www.smpte-ra.org/schemas/428-7/2014/DCST" xmlns:xs="http://www.w3.org/2001/XMLSchema">
+	<Id>urn:uuid:6382e2f3-8d75-441a-8324-4d0713549056</Id>
+	<ContentTitleText>Stereoscopic Subtitles: timeline01</ContentTitleText>
+	<AnnotationText>3D subs made with Davinci</AnnotationText>
+	<IssueDate>2025-01-28T20:47:47.904-00:00</IssueDate>
+	<ReelNumber>1</ReelNumber>
+	<Language>en</Language>
+	<EditRate>24 1</EditRate>
+	<TimeCodeRate>24</TimeCodeRate>
+	<StartTime>00:00:00:00</StartTime>
+	<DisplayType>MainSubtitle</DisplayType>
+	<LoadFont ID="MyFont">urn:uuid:d621dedd-089d-4d1f-8c24-fb976e1439df</LoadFont>
+	<SubtitleList>
+		<Font ID="MyFont" Color="FFFFFFFF" Weight="normal" Size="45">
+			<Subtitle SpotNumber="1" TimeIn="00:00:10:00" TimeOut="00:00:15:00">
+				<Text Valign="bottom" Vposition="20.00" Zposition="0.0">subtitle - position 0 - subtitle</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="2" TimeIn="00:00:15:00" TimeOut="00:00:20:00">
+				<Text Valign="bottom" Vposition="20.00" Zposition="-0.5">subtitle - position -0.5 - subtitle</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="3" TimeIn="00:00:20:00" TimeOut="00:00:25:00">
+				<Text Valign="bottom" Vposition="20.00" Zposition="-1">subtitle - position -1 - subtitle</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="4" TimeIn="00:00:25:00" TimeOut="00:00:30:00">
+				<Text Valign="bottom" Vposition="20.00" Zposition="-1.5">subtitle - position -1.5 - subtitle</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="5" TimeIn="00:00:30:00" TimeOut="00:00:35:00">
+				<Text Valign="bottom" Vposition="20.00" Zposition="-2.0">subtitle - position -2 - subtitle</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="6" TimeIn="00:00:35:00" TimeOut="00:00:40:00">
+				<Text Valign="bottom" Vposition="20.00" Zposition="0.0">subtitle - position 0 - subtitle</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="7" TimeIn="00:00:40:00" TimeOut="00:00:45:00">
+				<Text Valign="bottom" Vposition="20.00" Zposition="0.5">subtitle - position 0.5 - subtitle</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="8" TimeIn="00:00:45:00" TimeOut="00:00:50:00">
+				<Text Valign="bottom" Vposition="20.00" Zposition="1.0">subtitle - position 1 - subtitle</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="9" TimeIn="00:00:50:00" TimeOut="00:00:55:00">
+				<Text Valign="bottom" Vposition="20.00" Zposition="1.5">subtitle - position 1.5 - subtitle</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="10" TimeIn="00:00:55:00" TimeOut="00:01:00:00">
+				<Text Valign="bottom" Vposition="20.00" Zposition="2.0">subtitle - position 2 - subtitle</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="11" TimeIn="00:01:05:00" TimeOut="00:01:20:00">
+				<LoadVariableZ ID="Zvector1">-2.0:120 0.0:120 2.0:120</LoadVariableZ>
+				<Text Valign="bottom" Vposition="10.00" Zposition="-2.0" VariableZ="Zvector1">animation -2 to 0 to 2</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="12" TimeIn="00:01:24:00" TimeOut="00:01:39:00">
+				<LoadVariableZ ID="Zvector2">0.0:120 2.0:120 -2.0:120</LoadVariableZ>
+				<Text Valign="bottom" Vposition="10.00" Zposition="0.0" VariableZ="Zvector2">animation 0 to 2 to - 2</Text>
+			</Subtitle>
+			<Subtitle SpotNumber="13" TimeIn="00:01:42:13" TimeOut="00:01:57:13">
+				<LoadVariableZ ID="Zvector3">2.0:180 0.0:180</LoadVariableZ>
+				<Text Valign="bottom" Vposition="10.00" Zposition="2.0" VariableZ="Zvector3">animation 2 to 0</Text>
+			</Subtitle>
+		</Font>
+	</SubtitleList>
+</SubtitleReel>
\ No newline at end of file
diff --git a/test/data/subtitles_with_vZani_parsed.xml b/test/data/subtitles_with_vZani_parsed.xml
new file mode 100644
index 00000000..7c9c797d
--- /dev/null
+++ b/test/data/subtitles_with_vZani_parsed.xml
@@ -0,0 +1,59 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<SubtitleReel xmlns="http://www.smpte-ra.org/schemas/428-7/2014/DCST">
+  <Id>urn:uuid:6382e2f3-8d75-441a-8324-4d0713549056</Id>
+  <ContentTitleText>Stereoscopic Subtitles: timeline01</ContentTitleText>
+  <AnnotationText>3D subs made with Davinci</AnnotationText>
+  <IssueDate>2025-01-28T20:47:47</IssueDate>
+  <ReelNumber>1</ReelNumber>
+  <Language>en</Language>
+  <EditRate>24 1</EditRate>
+  <TimeCodeRate>24</TimeCodeRate>
+  <StartTime>00:00:00:00</StartTime>
+  <LoadFont ID="MyFont">urn:uuid:d621dedd-089d-4d1f-8c24-fb976e1439df</LoadFont>
+  <SubtitleList>
+    <Font AspectAdjust="1.0" Color="FFFFFFFF" Effect="none" EffectColor="FF000000" ID="MyFont" Italic="no" Script="normal" Size="45" Underline="no" Weight="normal">
+      <Subtitle SpotNumber="1" TimeIn="00:00:10:00" TimeOut="00:00:15:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <Text Valign="bottom" Vposition="20">subtitle - position 0 - subtitle</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="2" TimeIn="00:00:15:00" TimeOut="00:00:20:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <Text Valign="bottom" Vposition="20" Zposition="-0.5">subtitle - position -0.5 - subtitle</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="3" TimeIn="00:00:20:00" TimeOut="00:00:25:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <Text Valign="bottom" Vposition="20" Zposition="-1">subtitle - position -1 - subtitle</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="4" TimeIn="00:00:25:00" TimeOut="00:00:30:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <Text Valign="bottom" Vposition="20" Zposition="-1.5">subtitle - position -1.5 - subtitle</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="5" TimeIn="00:00:30:00" TimeOut="00:00:35:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <Text Valign="bottom" Vposition="20" Zposition="-2">subtitle - position -2 - subtitle</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="6" TimeIn="00:00:35:00" TimeOut="00:00:40:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <Text Valign="bottom" Vposition="20">subtitle - position 0 - subtitle</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="7" TimeIn="00:00:40:00" TimeOut="00:00:45:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <Text Valign="bottom" Vposition="20" Zposition="0.5">subtitle - position 0.5 - subtitle</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="8" TimeIn="00:00:45:00" TimeOut="00:00:50:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <Text Valign="bottom" Vposition="20" Zposition="1">subtitle - position 1 - subtitle</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="9" TimeIn="00:00:50:00" TimeOut="00:00:55:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <Text Valign="bottom" Vposition="20" Zposition="1.5">subtitle - position 1.5 - subtitle</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="10" TimeIn="00:00:55:00" TimeOut="00:01:00:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <Text Valign="bottom" Vposition="20" Zposition="2">subtitle - position 2 - subtitle</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="11" TimeIn="00:01:05:00" TimeOut="00:01:20:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <LoadVariableZ ID="Zvector1">-2.0:120 0.0:120 2.0:120</LoadVariableZ>
+        <Text Valign="bottom" Vposition="10" Zposition="-2" VariableZ="Zvector1">animation -2 to 0 to 2</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="12" TimeIn="00:01:24:00" TimeOut="00:01:39:00" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <LoadVariableZ ID="Zvector2">0.0:120 2.0:120 -2.0:120</LoadVariableZ>
+        <Text Valign="bottom" Vposition="10" VariableZ="Zvector2">animation 0 to 2 to - 2</Text>
+      </Subtitle>
+      <Subtitle SpotNumber="13" TimeIn="00:01:42:13" TimeOut="00:01:57:13" FadeUpTime="00:00:00:02" FadeDownTime="00:00:00:02">
+        <LoadVariableZ ID="Zvector3">2.0:180 0.0:180</LoadVariableZ>
+        <Text Valign="bottom" Vposition="10" Zposition="2" VariableZ="Zvector3">animation 2 to 0</Text>
+      </Subtitle>
+    </Font>
+  </SubtitleList>
+</SubtitleReel>
diff --git a/test/decryption_test.cc b/test/decryption_test.cc
index 3bb62d21..2b34cd25 100644
--- a/test/decryption_test.cc
+++ b/test/decryption_test.cc
@@ -191,7 +191,7 @@ BOOST_AUTO_TEST_CASE (decryption_test2)
 		dcp::Time(0, 0, 5, 0, 24),
 		0.5, dcp::HAlign::CENTER,
 		0.5, dcp::VAlign::CENTER,
-		0,
+		0, vector<dcp::Text::VariableZPosition>(),
 		dcp::Direction::LTR,
 		"Hello world",
 		dcp::Effect::NONE,
diff --git a/test/interop_subtitle_test.cc b/test/interop_subtitle_test.cc
index 2d7f4a43..27dcaf23 100644
--- a/test/interop_subtitle_test.cc
+++ b/test/interop_subtitle_test.cc
@@ -46,6 +46,7 @@ using std::dynamic_pointer_cast;
 using std::shared_ptr;
 using std::string;
 using std::vector;
+using boost::optional;
 
 
 /** Load some subtitle content from Interop XML and check that it is read correctly */
@@ -83,6 +84,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test1)
 				   0.15,
 				   dcp::VAlign::BOTTOM,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "My jacket was ",
 				   dcp::Effect::BORDER,
@@ -108,6 +110,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test1)
 				   0.15,
 				   dcp::VAlign::BOTTOM,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "Idi Amin's",
 				   dcp::Effect::BORDER,
@@ -136,6 +139,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test1)
 				   0.21,
 				   dcp::VAlign::BOTTOM,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "My corset was H.M. The Queen's",
 				   dcp::Effect::BORDER,
@@ -161,6 +165,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test1)
 				   0.15,
 				   dcp::VAlign::BOTTOM,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "My large wonderbra",
 				   dcp::Effect::BORDER,
@@ -189,6 +194,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test1)
 				   0.15,
 				   dcp::VAlign::BOTTOM,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "Once belonged to the Shah",
 				   dcp::Effect::BORDER,
@@ -217,6 +223,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test1)
 				   0.15,
 				   dcp::VAlign::BOTTOM,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "And these are Roy Hattersley's jeans",
 				   dcp::Effect::BORDER,
@@ -251,6 +258,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.89,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "At afternoon tea with John Peel",
 				   dcp::Effect::BORDER,
@@ -276,6 +284,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.95,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "I enquired if his accent was real",
 				   dcp::Effect::BORDER,
@@ -304,6 +313,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.89,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "He said \"out of the house",
 				   dcp::Effect::BORDER,
@@ -329,6 +339,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.95,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "I'm incredibly scouse",
 				   dcp::Effect::BORDER,
@@ -357,6 +368,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.89,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "At home it depends how I feel.\"",
 				   dcp::Effect::BORDER,
@@ -382,6 +394,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.95,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "I spent a long weekend in Brighton",
 				   dcp::Effect::BORDER,
@@ -410,6 +423,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.89,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::RTL,
 				   "With the legendary Miss Enid Blyton",
 				   dcp::Effect::BORDER,
@@ -435,6 +449,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.95,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::TTB,
 				   "She said \"you be Noddy",
 				   dcp::Effect::BORDER,
@@ -463,6 +478,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.89,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::BTT,
 				   "That curious creature the Sphinx",
 				   dcp::Effect::BORDER,
@@ -488,6 +504,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.95,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "Is smarter than anyone thinks",
 				   dcp::Effect::BORDER,
@@ -516,6 +533,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.89,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "It sits there and smirks",
 				   dcp::Effect::BORDER,
@@ -541,6 +559,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.95,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "And you don't think it works",
 				   dcp::Effect::BORDER,
@@ -569,6 +588,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.89,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "Then when you're not looking, it winks.",
 				   dcp::Effect::BORDER,
@@ -594,6 +614,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.95,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "When it snows you will find Sister Sledge",
 				   dcp::Effect::BORDER,
@@ -622,6 +643,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.89,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "Out mooning, at night, on the ledge",
 				   dcp::Effect::BORDER,
@@ -647,6 +669,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.95,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "One storey down",
 				   dcp::Effect::BORDER,
@@ -675,6 +698,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.89,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "HELLO",
 				   dcp::Effect::BORDER,
@@ -700,6 +724,7 @@ BOOST_AUTO_TEST_CASE (read_interop_subtitle_test2)
 				   0.95,
 				   dcp::VAlign::TOP,
 				   0,
+				   vector<dcp::Text::VariableZPosition>(),
 				   dcp::Direction::LTR,
 				   "WORLD",
 				   dcp::Effect::BORDER,
@@ -747,6 +772,7 @@ BOOST_AUTO_TEST_CASE (write_interop_subtitle_test)
 			0.8,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"Hello world",
 			dcp::Effect::NONE,
@@ -774,6 +800,7 @@ BOOST_AUTO_TEST_CASE (write_interop_subtitle_test)
 			0.4,
 			dcp::VAlign::BOTTOM,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"What's going ",
 			dcp::Effect::BORDER,
@@ -801,6 +828,7 @@ BOOST_AUTO_TEST_CASE (write_interop_subtitle_test)
 			0.4,
 			dcp::VAlign::BOTTOM,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"on",
 			dcp::Effect::BORDER,
@@ -862,6 +890,7 @@ BOOST_AUTO_TEST_CASE (write_interop_subtitle_test2)
 			0.8,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"Hello world",
 			dcp::Effect::NONE,
@@ -889,6 +918,7 @@ BOOST_AUTO_TEST_CASE (write_interop_subtitle_test2)
 			0.4,
 			dcp::VAlign::BOTTOM,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"What's going on",
 			dcp::Effect::BORDER,
@@ -944,6 +974,7 @@ BOOST_AUTO_TEST_CASE (write_interop_subtitle_test3)
 			0.8,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Time (0, 0, 0, 0, 24),
 			dcp::Time (0, 0, 0, 0, 24)
 			)
diff --git a/test/load_variable_z_test.cc b/test/load_variable_z_test.cc
index 8448480f..07c45a57 100644
--- a/test/load_variable_z_test.cc
+++ b/test/load_variable_z_test.cc
@@ -33,6 +33,7 @@
 
 
 #include "load_variable_z.h"
+#include "smpte_text_asset.h"
 #include "warnings.h"
 #include "compose.hpp"
 LIBDCP_DISABLE_WARNINGS
@@ -89,3 +90,12 @@ BOOST_AUTO_TEST_CASE(variable_z_test)
 	made.set_positions({{-0.6, 2}, {4.2, 9}, {5, 1}});
 	BOOST_CHECK_EQUAL(xml(made), "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<LoadVariableZ ID=\"baz\">-0.6:2 4.2:9 5.0</LoadVariableZ>\n");
 }
+
+
+BOOST_AUTO_TEST_CASE(variable_z_pass_through)
+{
+	dcp::SMPTETextAsset asset("test/data/subtitles_with_vZani.xml");
+	BOOST_CHECK_EQUAL(asset.xml_as_string(), dcp::file_to_string("test/data/subtitles_with_vZani_parsed.xml"));
+}
+
+
diff --git a/test/shared_subtitle_test.cc b/test/shared_subtitle_test.cc
index 82595cd0..1a7ba853 100644
--- a/test/shared_subtitle_test.cc
+++ b/test/shared_subtitle_test.cc
@@ -108,7 +108,7 @@ BOOST_AUTO_TEST_CASE (pull_fonts_test1)
 	auto root = make_shared<dcp::order::Part>(shared_ptr<dcp::order::Part>());
 	auto sub1 = make_shared<dcp::order::Subtitle>(root, dcp::Time(), dcp::Time(), dcp::Time(), dcp::Time());
 	root->children.push_back (sub1);
-	auto text1 = make_shared<dcp::order::Text>(sub1, dcp::HAlign::CENTER, 0, dcp::VAlign::TOP, 0, 0, dcp::Direction::LTR, std::vector<dcp::Ruby>());
+	auto text1 = make_shared<dcp::order::Text>(sub1, dcp::HAlign::CENTER, 0, dcp::VAlign::TOP, 0, 0, optional<string>(), dcp::Direction::LTR, std::vector<dcp::Ruby>());
 	sub1->children.push_back (text1);
 	text1->font._values["font"] = "Inconsolata";
 	text1->font._values["size"] = "42";
@@ -127,11 +127,11 @@ BOOST_AUTO_TEST_CASE (pull_fonts_test2)
 	auto root = make_shared<dcp::order::Part>(shared_ptr<dcp::order::Part> ());
 	auto sub1 = make_shared<dcp::order::Subtitle>(root, dcp::Time(), dcp::Time(), dcp::Time(), dcp::Time());
 	root->children.push_back (sub1);
-	auto text1 = make_shared<dcp::order::Text>(sub1, dcp::HAlign::CENTER, 0, dcp::VAlign::TOP, 0, 0, dcp::Direction::LTR, std::vector<dcp::Ruby>());
+	auto text1 = make_shared<dcp::order::Text>(sub1, dcp::HAlign::CENTER, 0, dcp::VAlign::TOP, 0, 0, optional<string>(), dcp::Direction::LTR, std::vector<dcp::Ruby>());
 	sub1->children.push_back (text1);
 	text1->font._values["font"] = "Inconsolata";
 	text1->font._values["size"] = "42";
-	auto text2 = make_shared<dcp::order::Text>(sub1, dcp::HAlign::CENTER, 0, dcp::VAlign::TOP, 0, 0, dcp::Direction::LTR, std::vector<dcp::Ruby>());
+	auto text2 = make_shared<dcp::order::Text>(sub1, dcp::HAlign::CENTER, 0, dcp::VAlign::TOP, 0, 0, optional<string>(), dcp::Direction::LTR, std::vector<dcp::Ruby>());
 	sub1->children.push_back (text2);
 	text2->font._values["font"] = "Inconsolata";
 	text2->font._values["size"] = "48";
@@ -152,7 +152,7 @@ BOOST_AUTO_TEST_CASE (pull_fonts_test3)
 	auto root = make_shared<dcp::order::Part>(shared_ptr<dcp::order::Part> ());
 	auto sub1 = make_shared<dcp::order::Subtitle>(root, dcp::Time(), dcp::Time(), dcp::Time(), dcp::Time());
 	root->children.push_back (sub1);
-	auto text1 = make_shared<dcp::order::Text>(sub1, dcp::HAlign::CENTER, 0, dcp::VAlign::TOP, 0, 0, dcp::Direction::LTR, std::vector<dcp::Ruby>());
+	auto text1 = make_shared<dcp::order::Text>(sub1, dcp::HAlign::CENTER, 0, dcp::VAlign::TOP, 0, 0, optional<string>(), dcp::Direction::LTR, std::vector<dcp::Ruby>());
 	sub1->children.push_back (text1);
 	dcp::order::Font font;
 	font._values["font"] = "Inconsolata";
diff --git a/test/smpte_subtitle_test.cc b/test/smpte_subtitle_test.cc
index e1dabc44..5aa6bea6 100644
--- a/test/smpte_subtitle_test.cc
+++ b/test/smpte_subtitle_test.cc
@@ -66,6 +66,7 @@ BOOST_AUTO_TEST_CASE (smpte_subtitle_id_test)
 			0.5,
 			dcp::VAlign::CENTER,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"Hello",
 			dcp::Effect::NONE,
@@ -196,6 +197,7 @@ BOOST_AUTO_TEST_CASE (write_smpte_subtitle_test)
 			0.8,
 			dcp::VAlign::TOP,
 			0.3,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"Hello world",
 			dcp::Effect::NONE,
@@ -223,6 +225,7 @@ BOOST_AUTO_TEST_CASE (write_smpte_subtitle_test)
 			0.4,
 			dcp::VAlign::BOTTOM,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::RTL,
 			"What's going ",
 			dcp::Effect::BORDER,
@@ -250,6 +253,7 @@ BOOST_AUTO_TEST_CASE (write_smpte_subtitle_test)
 			0.4,
 			dcp::VAlign::BOTTOM,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::RTL,
 			"on",
 			dcp::Effect::BORDER,
@@ -318,6 +322,7 @@ BOOST_AUTO_TEST_CASE (write_smpte_subtitle_test2)
 			0.8,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"Testing is ",
 			dcp::Effect::NONE,
@@ -345,6 +350,7 @@ BOOST_AUTO_TEST_CASE (write_smpte_subtitle_test2)
 			0.8,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"really",
 			dcp::Effect::NONE,
@@ -372,6 +378,7 @@ BOOST_AUTO_TEST_CASE (write_smpte_subtitle_test2)
 			0.8,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			" fun",
 			dcp::Effect::NONE,
@@ -399,6 +406,7 @@ BOOST_AUTO_TEST_CASE (write_smpte_subtitle_test2)
 			0.9,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"This is the ",
 			dcp::Effect::NONE,
@@ -426,6 +434,7 @@ BOOST_AUTO_TEST_CASE (write_smpte_subtitle_test2)
 			0.9,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"second",
 			dcp::Effect::NONE,
@@ -453,6 +462,7 @@ BOOST_AUTO_TEST_CASE (write_smpte_subtitle_test2)
 			0.9,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			" line",
 			dcp::Effect::NONE,
@@ -511,6 +521,7 @@ BOOST_AUTO_TEST_CASE (write_smpte_subtitle_test3)
 			0.8,
 			dcp::VAlign::TOP,
 			-88,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Time (0, 0, 0, 0, 24),
 			dcp::Time (0, 0, 0, 0, 24)
 			)
@@ -568,6 +579,7 @@ BOOST_AUTO_TEST_CASE (write_subtitles_in_vertical_order_with_top_alignment)
 			0.8,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"Top line",
 			dcp::Effect::NONE,
@@ -595,6 +607,7 @@ BOOST_AUTO_TEST_CASE (write_subtitles_in_vertical_order_with_top_alignment)
 			0.9,
 			dcp::VAlign::TOP,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"Bottom line",
 			dcp::Effect::NONE,
@@ -658,6 +671,7 @@ BOOST_AUTO_TEST_CASE (write_subtitles_in_vertical_order_with_bottom_alignment)
 			0.8,
 			dcp::VAlign::BOTTOM,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"Top line",
 			dcp::Effect::NONE,
@@ -685,6 +699,7 @@ BOOST_AUTO_TEST_CASE (write_subtitles_in_vertical_order_with_bottom_alignment)
 			0.7,
 			dcp::VAlign::BOTTOM,
 			0,
+			vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"Bottom line",
 			dcp::Effect::NONE,
@@ -782,3 +797,13 @@ BOOST_AUTO_TEST_CASE(smpte_subtitle_intrinsic_duration_read_correctly)
 	BOOST_CHECK_EQUAL(check.intrinsic_duration(), duration);
 }
 
+
+
+BOOST_AUTO_TEST_CASE(pass_through_smpte_subtitle_with_variable_z)
+{
+	auto source = "test/data/subtitles_with_vZani.xml";
+	dcp::SMPTETextAsset test("test/data/subtitles_with_vZani.xml");
+	/* _parsed is a version of the source with some changes made by libdcp that are OK */
+	check_xml(dcp::file_to_string("test/data/subtitles_with_vZani_parsed.xml"), test.xml_as_string(), { "IssueDate" }, true);
+}
+
diff --git a/test/test.cc b/test/test.cc
index 0de9c73c..42619683 100644
--- a/test/test.cc
+++ b/test/test.cc
@@ -410,6 +410,7 @@ simple_text()
 		0.8,
 		dcp::VAlign::TOP,
 		0,
+		vector<dcp::Text::VariableZPosition>(),
 		dcp::Direction::LTR,
 		"Hello world",
 		dcp::Effect::NONE,
diff --git a/test/verify_test.cc b/test/verify_test.cc
index 3352b472..6c09cbe0 100644
--- a/test/verify_test.cc
+++ b/test/verify_test.cc
@@ -2092,7 +2092,7 @@ add_test_subtitle (shared_ptr<dcp::TextAsset> asset, int start_frame, int end_fr
 			dcp::HAlign::CENTER,
 			v_position,
 			v_align,
-			0,
+			0, vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			text,
 			dcp::Effect::NONE,
@@ -5896,7 +5896,7 @@ BOOST_AUTO_TEST_CASE(overlapping_subtitles)
 			dcp::Time(0, 0, 8, 0, 24),
 			0, dcp::HAlign::CENTER,
 			0, dcp::VAlign::CENTER,
-			0,
+			0, vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"",
 			dcp::Effect::NONE, dcp::Colour{}, dcp::Time{}, dcp::Time{}, 0, vector<dcp::Ruby>{}
@@ -5909,7 +5909,7 @@ BOOST_AUTO_TEST_CASE(overlapping_subtitles)
 			dcp::Time(0, 0, 4, 0, 24),
 			0, dcp::HAlign::CENTER,
 			0, dcp::VAlign::CENTER,
-			0,
+			0, vector<dcp::Text::VariableZPosition>(),
 			dcp::Direction::LTR,
 			"Hello",
 			dcp::Effect::NONE, dcp::Colour{}, dcp::Time{}, dcp::Time{}, 0, vector<dcp::Ruby>{}