Improve handling of image subtitle IDs in XML (DoM bug #1965)backport

When reading/writing the XML for image subtitles, we assumed that
the content of the <Image> tag is just the ID of the PNG in the MXF,
without any prefix.

DoM bug #1965 mentions a DCP where this is not the case, and SMPTE
429-5-2009 has an example where there is urn:uuid: in the XML.

This change makes DoM write this urn:uuid: prefix, and accept it if
it's present (but not complain if it's not).

If the urn:uuid: _is_ required in the field, it's a bit surprising
that nobody has complained up to this point.  Maybe nobody noticed,
or nobody reported it.

Cherry-picked from 098007a1ee6a46b6ff11398f94faff5c85951da4 in master.

2 files changed, 25 insertions, 4 deletions

diff --git a/src/subtitle_asset.cc b/src/subtitle_asset.cc
index 083a8040..aeec99d7 100644
--- a/src/subtitle_asset.cc
+++ b/src/subtitle_asset.cc
@@ -385,13 +385,33 @@ SubtitleAsset::maybe_add_subtitle (string text, list<ParseState> const & parse_s
 				)
 			);
 		break;
-	case ParseState::IMAGE:
+	case ParseState::Type::IMAGE:
+	{
+		switch (standard) {
+		case INTEROP:
+			if (text.size() >= 4) {
+				/* Remove file extension */
+				text = text.substr(0, text.size() - 4);
+			}
+			break;
+		case SMPTE:
+			/* It looks like this urn:uuid: is required, but DoM wasn't expecting it (and not writing it)
+			 * until around 2.15.140 so I guess either:
+			 *   a) it is not (always) used in the field, or
+			 *   b) nobody noticed / complained.
+			 */
+			if (text.substr(0, 9) == "urn:uuid:") {
+				text = text.substr(9);
+			}
+			break;
+		}
+
 		/* Add a subtitle with no image data and we'll fill that in later */
 		_subtitles.push_back (
 			shared_ptr<Subtitle> (
 				new SubtitleImage (
-					Data (),
-					standard == INTEROP ? text.substr(0, text.size() - 4) : text,
+					Data(),
+					text,
 					ps.in.get(),
 					ps.out.get(),
 					ps.h_position.get_value_or(0),
@@ -405,6 +425,7 @@ SubtitleAsset::maybe_add_subtitle (string text, list<ParseState> const & parse_s
 			);
 		break;
 	}
+	}
 }
 
 list<shared_ptr<Subtitle> >
diff --git a/src/subtitle_asset_internal.cc b/src/subtitle_asset_internal.cc
index 7b9e18e9..25e03f0b 100644
--- a/src/subtitle_asset_internal.cc
+++ b/src/subtitle_asset_internal.cc
@@ -239,7 +239,7 @@ order::Image::as_xml (xmlpp::Element* parent, Context& context) const
 
 	position_align (e, context, _h_align, _h_position, _v_align, _v_position);
 	if (context.standard == SMPTE) {
-		e->add_child_text (_id);
+		e->add_child_text ("urn:uuid:" + _id);
 	} else {
 		e->add_child_text (_id + ".png");
 	}