Properly parse SRT subtitles in MKV files

Fixes #436.

Author: arch1t3cht

src/mkv_wrap.cpp

@@ -40,6 +40,7 @@
 #include "dialog_progress.h"
 #include "MatroskaParser.h"
 #include "options.h"
+#include "subtitle_format_srt.h"
 
 #include <libaegisub/ass/time.h>
 #include <libaegisub/file_mapping.h>
@@ -123,6 +124,8 @@ static bool read_subtitles(agi::ProgressSink *ps, MatroskaFile *file, MkvStdIO *
 
 	std::vector<char> uncompBuf(cs ? 256 : 0);
 
+	SrtTagParser srtParser;
+
 	while (mkv_ReadFrame(file, 0, &rt, &startTime, &endTime, &filePos, &frameSize, &frameFlags) == 0) {
 		if (ps->IsCancelled()) return true;
 		if (frameSize == 0) continue;
@@ -179,7 +182,7 @@ static bool read_subtitles(agi::ProgressSink *ps, MatroskaFile *file, MkvStdIO *
 			auto line = agi::format("Dialogue: 0,%s,%s,Default,,0,0,0,,%s"
 				, subStart.GetAssFormatted()
 				, subEnd.GetAssFormatted()
-				, readBuf);
+				, srtParser.ToAss(std::string(readBuf)));
 			boost::replace_all(line, "\r\n", "\\N");
 			boost::replace_all(line, "\r", "\\N");
 			boost::replace_all(line, "\n", "\\N");

src/subtitle_format_srt.cpp

@@ -48,7 +48,6 @@
 #include <boost/algorithm/string/predicate.hpp>
 #include <boost/algorithm/string/replace.hpp>
 #include <boost/algorithm/string/trim.hpp>
-#include <boost/regex.hpp>
 
 DEFINE_EXCEPTION(SRTParseError, SubtitleFormatParseError);
 
@@ -119,169 +118,154 @@ struct ToggleTag {
 	}
 };
 
-class SrtTagParser {
-	struct FontAttribs {
-		std::string face;
-		std::string size;
-		std::string color;
-	};
+std::string WriteSRTTime(agi::Time const& ts)
+{
+	return ts.GetSrtFormatted();
+}
 
-	const boost::regex tag_matcher;
-	const boost::regex attrib_matcher;
-	const boost::regex is_quoted;
+}
 
-public:
-	SrtTagParser()
-	: tag_matcher("^(.*?)<(/?b|/?i|/?u|/?s|/?font)([^>]*)>(.*)$", boost::regex::icase)
-	, attrib_matcher(R"(^[[:space:]]+(face|size|color)=('[^']*'|"[^"]*"|[^[:space:]]+))", boost::regex::icase)
-	, is_quoted(R"(^(['"]).*\1$)")
-	{
-	}
+SrtTagParser::SrtTagParser()
+: tag_matcher("^(.*?)<(/?b|/?i|/?u|/?s|/?font)([^>]*)>(.*)$", boost::regex::icase)
+, attrib_matcher(R"(^[[:space:]]+(face|size|color)=('[^']*'|"[^"]*"|[^[:space:]]+))", boost::regex::icase)
+, is_quoted(R"(^(['"]).*\1$)")
+{}
+
+std::string SrtTagParser::ToAss(std::string srt) {
+	ToggleTag bold('b');
+	ToggleTag italic('i');
+	ToggleTag underline('u');
+	ToggleTag strikeout('s');
+	std::vector<FontAttribs> font_stack;
+
+	std::string ass; // result to be built
 
-	std::string ToAss(std::string srt)
+	while (!srt.empty())
 	{
-		ToggleTag bold('b');
-		ToggleTag italic('i');
-		ToggleTag underline('u');
-		ToggleTag strikeout('s');
-		std::vector<FontAttribs> font_stack;
+		boost::smatch result;
+		if (!regex_match(srt, result, tag_matcher))
+		{
+			// no more tags could be matched, end of string
+			ass.append(srt);
+			break;
+		}
 
-		std::string ass; // result to be built
+		// we found a tag, translate it
+		std::string pre_text  = result.str(1);
+		std::string tag_name  = result.str(2);
+		std::string tag_attrs = result.str(3);
+		std::string post_text = result.str(4);
 
-		while (!srt.empty())
+		// the text before the tag goes through unchanged
+		ass.append(pre_text);
+		// the text after the tag is the input for next iteration
+		srt = post_text;
+
+		boost::to_lower(tag_name);
+		switch (type_from_name(tag_name))
 		{
-			boost::smatch result;
-			if (!regex_match(srt, result, tag_matcher))
+		case TagType::BOLD_OPEN:       bold.Open(ass);       break;
+		case TagType::BOLD_CLOSE:      bold.Close(ass);      break;
+		case TagType::ITALICS_OPEN:    italic.Open(ass);     break;
+		case TagType::ITALICS_CLOSE:   italic.Close(ass);    break;
+		case TagType::UNDERLINE_OPEN:  underline.Open(ass);  break;
+		case TagType::UNDERLINE_CLOSE: underline.Close(ass); break;
+		case TagType::STRIKEOUT_OPEN:  strikeout.Open(ass);  break;
+		case TagType::STRIKEOUT_CLOSE: strikeout.Close(ass); break;
+		case TagType::FONT_OPEN:
 			{
-				// no more tags could be matched, end of string
-				ass.append(srt);
-				break;
-			}
-
-			// we found a tag, translate it
-			std::string pre_text  = result.str(1);
-			std::string tag_name  = result.str(2);
-			std::string tag_attrs = result.str(3);
-			std::string post_text = result.str(4);
+				// new attributes to fill in
+				FontAttribs new_attribs;
+				FontAttribs old_attribs;
+				// start out with any previous ones on stack
+				if (font_stack.size() > 0)
+					old_attribs = font_stack.back();
+				new_attribs = old_attribs;
+				// now find all attributes on this font tag
+				boost::smatch result;
+				while (regex_search(tag_attrs, result, attrib_matcher))
+				{
+					// get attribute name and values
+					std::string attr_name = result.str(1);
+					std::string attr_value = result.str(2);
+
+					// clean them
+					boost::to_lower(attr_name);
+					if (regex_match(attr_value, is_quoted))
+						attr_value = attr_value.substr(1, attr_value.size() - 2);
+
+					// handle the attributes
+					if (attr_name == "face")
+						new_attribs.face = agi::format("{\\fn%s}", attr_value);
+					else if (attr_name == "size")
+						new_attribs.size = agi::format("{\\fs%s}", attr_value);
+					else if (attr_name == "color")
+						new_attribs.color = agi::format("{\\c%s}", agi::Color(attr_value).GetAssOverrideFormatted());
+
+					// remove this attribute to prepare for the next
+					tag_attrs = result.suffix().str();
+				}
 
-			// the text before the tag goes through unchanged
-			ass.append(pre_text);
-			// the text after the tag is the input for next iteration
-			srt = post_text;
+				// the attributes changed from old are then written out
+				if (new_attribs.face != old_attribs.face)
+					ass.append(new_attribs.face);
+				if (new_attribs.size != old_attribs.size)
+					ass.append(new_attribs.size);
+				if (new_attribs.color != old_attribs.color)
+					ass.append(new_attribs.color);
 
-			boost::to_lower(tag_name);
-			switch (type_from_name(tag_name))
+				// lastly dump the new attributes state onto the stack
+				font_stack.push_back(new_attribs);
+			}
+			break;
+		case TagType::FONT_CLOSE:
 			{
-			case TagType::BOLD_OPEN:       bold.Open(ass);       break;
-			case TagType::BOLD_CLOSE:      bold.Close(ass);      break;
-			case TagType::ITALICS_OPEN:    italic.Open(ass);     break;
-			case TagType::ITALICS_CLOSE:   italic.Close(ass);    break;
-			case TagType::UNDERLINE_OPEN:  underline.Open(ass);  break;
-			case TagType::UNDERLINE_CLOSE: underline.Close(ass); break;
-			case TagType::STRIKEOUT_OPEN:  strikeout.Open(ass);  break;
-			case TagType::STRIKEOUT_CLOSE: strikeout.Close(ass); break;
-			case TagType::FONT_OPEN:
+				// this requires a font stack entry
+				if (font_stack.empty())
+					break;
+				// get the current attribs
+				FontAttribs cur_attribs = font_stack.back();
+				// remove them from the stack
+				font_stack.pop_back();
+				// grab the old attributes if there are any
+				FontAttribs old_attribs;
+				if (font_stack.size() > 0)
+					old_attribs = font_stack.back();
+				// then restore the attributes to previous settings
+				if (cur_attribs.face != old_attribs.face)
 				{
-					// new attributes to fill in
-					FontAttribs new_attribs;
-					FontAttribs old_attribs;
-					// start out with any previous ones on stack
-					if (font_stack.size() > 0)
-						old_attribs = font_stack.back();
-					new_attribs = old_attribs;
-					// now find all attributes on this font tag
-					boost::smatch result;
-					while (regex_search(tag_attrs, result, attrib_matcher))
-					{
-						// get attribute name and values
-						std::string attr_name = result.str(1);
-						std::string attr_value = result.str(2);
-
-						// clean them
-						boost::to_lower(attr_name);
-						if (regex_match(attr_value, is_quoted))
-							attr_value = attr_value.substr(1, attr_value.size() - 2);
-
-						// handle the attributes
-						if (attr_name == "face")
-							new_attribs.face = agi::format("{\\fn%s}", attr_value);
-						else if (attr_name == "size")
-							new_attribs.size = agi::format("{\\fs%s}", attr_value);
-						else if (attr_name == "color")
-							new_attribs.color = agi::format("{\\c%s}", agi::Color(attr_value).GetAssOverrideFormatted());
-
-						// remove this attribute to prepare for the next
-						tag_attrs = result.suffix().str();
-					}
-
-					// the attributes changed from old are then written out
-					if (new_attribs.face != old_attribs.face)
-						ass.append(new_attribs.face);
-					if (new_attribs.size != old_attribs.size)
-						ass.append(new_attribs.size);
-					if (new_attribs.color != old_attribs.color)
-						ass.append(new_attribs.color);
-
-					// lastly dump the new attributes state onto the stack
-					font_stack.push_back(new_attribs);
+					if (old_attribs.face.empty())
+						ass.append("{\\fn}");
+					else
+						ass.append(old_attribs.face);
 				}
-				break;
-			case TagType::FONT_CLOSE:
+				if (cur_attribs.size != old_attribs.size)
 				{
-					// this requires a font stack entry
-					if (font_stack.empty())
-						break;
-					// get the current attribs
-					FontAttribs cur_attribs = font_stack.back();
-					// remove them from the stack
-					font_stack.pop_back();
-					// grab the old attributes if there are any
-					FontAttribs old_attribs;
-					if (font_stack.size() > 0)
-						old_attribs = font_stack.back();
-					// then restore the attributes to previous settings
-					if (cur_attribs.face != old_attribs.face)
-					{
-						if (old_attribs.face.empty())
-							ass.append("{\\fn}");
-						else
-							ass.append(old_attribs.face);
-					}
-					if (cur_attribs.size != old_attribs.size)
-					{
-						if (old_attribs.size.empty())
-							ass.append("{\\fs}");
-						else
-							ass.append(old_attribs.size);
-					}
-					if (cur_attribs.color != old_attribs.color)
-					{
-						if (old_attribs.color.empty())
-							ass.append("{\\c}");
-						else
-							ass.append(old_attribs.color);
-					}
+					if (old_attribs.size.empty())
+						ass.append("{\\fs}");
+					else
+						ass.append(old_attribs.size);
+				}
+				if (cur_attribs.color != old_attribs.color)
+				{
+					if (old_attribs.color.empty())
+						ass.append("{\\c}");
+					else
+						ass.append(old_attribs.color);
 				}
-				break;
-			default:
-				// unknown tag, replicate it in the output
-				ass.append("<").append(tag_name).append(tag_attrs).append(">");
-				break;
 			}
+			break;
+		default:
+			// unknown tag, replicate it in the output
+			ass.append("<").append(tag_name).append(tag_attrs).append(">");
+			break;
 		}
-
-		// make it a little prettier, join tag groups
-		boost::replace_all(ass, "}{", "");
-
-		return ass;
 	}
-};
 
-std::string WriteSRTTime(agi::Time const& ts)
-{
-	return ts.GetSrtFormatted();
-}
+	// make it a little prettier, join tag groups
+	boost::replace_all(ass, "}{", "");
 
+	return ass;
 }
 
 SRTSubtitleFormat::SRTSubtitleFormat()

src/subtitle_format_srt.h

@@ -32,10 +32,31 @@
 /// @ingroup subtitle_io
 ///
 
+#include <string>
+
 #include "subtitle_format.h"
 
+#include <boost/regex.hpp>
+
 class AssDialogue;
 
+class SrtTagParser {
+	struct FontAttribs {
+		std::string face;
+		std::string size;
+		std::string color;
+	};
+
+	const boost::regex tag_matcher;
+	const boost::regex attrib_matcher;
+	const boost::regex is_quoted;
+
+public:
+	SrtTagParser();
+
+	std::string ToAss(std::string srt);
+};
+
 class SRTSubtitleFormat final : public SubtitleFormat {
 	std::string ConvertTags(const AssDialogue *diag) const;
 public: