Add FFMETADATA1 export, with chapter and stop code information.

You can feed the output of this into ffmpeg, to produce (for example)
Matroska output with chapter markers. Stop codes are just listed as
comments at the moment.

This is a straight translation of my decode-vbi Python program.

scripts/test-decode

@@ -121,11 +121,12 @@ def run_ld_process_vbi(args):
 def run_ld_export_metadata(args):
     """Run ld-export-metadata."""
 
-    clean(args, ['.vits.csv', '.vbi.csv'])
+    clean(args, ['.vits.csv', '.vbi.csv', '.ffmetadata'])
 
     cmd = [src_dir + '/tools/ld-export-metadata/ld-export-metadata']
     cmd += ['--vits-csv', args.output + '.vits.csv']
     cmd += ['--vbi-csv', args.output + '.vbi.csv']
+    cmd += ['--ffmetadata', args.output + '.ffmetadata']
     cmd += [args.output + '.tbc.json']
     run_command(cmd)
 

tools/ld-export-metadata/ffmetadata.cpp

@@ -0,0 +1,147 @@
+/************************************************************************
+
+    ffmetadata.cpp
+
+    ld-export-metadata - Export JSON metadata into other formats
+    Copyright (C) 2019-2020 Adam Sampson
+
+    This file is part of ld-decode-tools.
+
+    ld-export-metadata 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 3 of the
+    License, or (at your option) any later version.
+
+    This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+************************************************************************/
+
+#include "ffmetadata.h"
+
+#include "vbidecoder.h"
+
+#include <QtGlobal>
+#include <QFile>
+#include <QTextStream>
+#include <set>
+#include <vector>
+
+using std::set;
+using std::vector;
+
+struct ChapterChange {
+    qint32 field;
+    qint32 chapter;
+};
+
+bool writeFfmetadata(LdDecodeMetaData &metaData, const QString &fileName)
+{
+    const auto videoParameters = metaData.getVideoParameters();
+
+    // We'll give positions using 0-based field indexes directly, rather than
+    // using the times encoded in the VBI, because we might be working with a
+    // capture of only part of a disc. Select the appropriate timebase to make
+    // this work.
+    const QString timeBase = videoParameters.isSourcePal ? "1/50" : "1001/60000";
+
+    // Scan through the fields in the input, collecting VBI information
+    vector<ChapterChange> chapterChanges;
+    set<qint32> stopCodes;
+    qint32 chapter = -1;
+    qint32 firstFieldIndex = 0;
+    VbiDecoder vbiDecoder;
+
+    for (qint32 fieldIndex = 0; fieldIndex < videoParameters.numberOfSequentialFields; fieldIndex++) {
+        // Get the (1-based) field
+        const auto field = metaData.getField(fieldIndex + 1);
+
+        // Codes may be in either field; we want the index of the first
+        if (field.isFirstField) {
+            firstFieldIndex = fieldIndex;
+        }
+
+        // Decode this field's VBI
+        const auto vbi = vbiDecoder.decode(field.vbi.vbiData[0], field.vbi.vbiData[1], field.vbi.vbiData[2]);
+
+        if (vbi.chNo != -1 && vbi.chNo != chapter) {
+            // Chapter change
+            chapter = vbi.chNo;
+            chapterChanges.emplace_back(ChapterChange {firstFieldIndex, chapter});
+        }
+
+        if (vbi.picStop) {
+            // Stop code
+            stopCodes.insert(firstFieldIndex);
+        }
+    }
+
+    // Add a dummy change at the end of the input, so we can get the length of
+    // the last chapter
+    chapterChanges.emplace_back(ChapterChange {videoParameters.numberOfSequentialFields, -1});
+
+    // Because chapter markers have no error detection, a corrupt marker will
+    // result in a spurious chapter change. Remove suspiciously short chapters.
+    // XXX This could be smarter for sequences like 1 1 1 1 *2 2 3* 2 2 2 2
+    vector<ChapterChange> cleanChanges;
+    for (qint32 i = 0; i < static_cast<qint32>(chapterChanges.size() - 1); i++) {
+        const auto &change = chapterChanges[i];
+        const auto &nextChange = chapterChanges[i + 1];
+
+        if ((nextChange.field - change.field) < 10) {
+            // Chapters should be at least 30 tracks (= 60 or more fields) long. So
+            // this is too short -- drop it.
+        } else if ((!cleanChanges.empty()) && (change.chapter == cleanChanges.back().chapter)) {
+            // Change to the same chapter - drop
+        } else {
+            // Keep
+            cleanChanges.emplace_back(change);
+        }
+    }
+
+    // Keep the dummy change
+    cleanChanges.emplace_back(chapterChanges.back());
+
+    // Open the output file
+    QFile file(fileName);
+    if (!file.open(QFile::WriteOnly | QFile::Text)) {
+        qDebug("writeFfmetadata: Could not open file for output");
+        return false;
+    }
+    QTextStream stream(&file);
+    stream.setCodec("UTF-8");
+
+    // Write the header
+    stream << ";FFMETADATA1\n";
+
+    // Write the chapter changes, skipping the dummy one at the end
+    for (qint32 i = 0; i < static_cast<qint32>(cleanChanges.size() - 1); i++) {
+        const auto &change = cleanChanges[i];
+        const auto &nextChange = cleanChanges[i + 1];
+
+        stream << "\n";
+        stream << "[CHAPTER]\n";
+        stream << "TIMEBASE=" << timeBase << "\n";
+        stream << "START=" << change.field << "\n";
+        stream << "END=" << (nextChange.field - 1) << "\n";
+        stream << "title=" << QString("Chapter %1").arg(change.chapter) << "\n";
+    }
+
+    if (!stopCodes.empty()) {
+        // Write the stop codes, as comments
+        // XXX Is there a way to represent these properly?
+        stream << "\n";
+        for (qint32 field : stopCodes) {
+            stream << "; Stop code at " << field << "\n";
+        }
+    }
+
+    // Done!
+    file.close();
+    return true;
+}

tools/ld-export-metadata/ffmetadata.h

@@ -0,0 +1,43 @@
+/************************************************************************
+
+    ffmetadata.h
+
+    ld-export-metadata - Export JSON metadata into other formats
+    Copyright (C) 2020 Adam Sampson
+
+    This file is part of ld-decode-tools.
+
+    ld-export-metadata 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 3 of the
+    License, or (at your option) any later version.
+
+    This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+************************************************************************/
+
+#ifndef FFMETADATA_H
+#define FFMETADATA_H
+
+#include <QString>
+
+#include "lddecodemetadata.h"
+
+/*!
+    Write an FFMETADATA1 file containing navigation information.
+
+    This is FFmpeg's generic metadata format, and can be used to provide
+    metadata for chapter-supporting formats like Matroska.
+    Format description: <https://ffmpeg.org/ffmpeg-formats.html#Metadata-1>
+
+    Returns true on success, false on failure.
+*/
+bool writeFfmetadata(LdDecodeMetaData &metaData, const QString &fileName);
+
+#endif

tools/ld-export-metadata/ld-export-metadata.pro

@@ -16,12 +16,14 @@ DEFINES += QT_DEPRECATED_WARNINGS
 
 SOURCES += \
     csv.cpp \
+    ffmetadata.cpp \
     main.cpp \
     ../library/tbc/lddecodemetadata.cpp \
     ../library/tbc/vbidecoder.cpp
 
 HEADERS += \
     csv.h \
+    ffmetadata.h \
     ../library/tbc/lddecodemetadata.h \
     ../library/tbc/vbidecoder.h
 

tools/ld-export-metadata/main.cpp

@@ -28,6 +28,7 @@
 #include <QCommandLineParser>
 
 #include "csv.h"
+#include "ffmetadata.h"
 
 #include "lddecodemetadata.h"
 
@@ -123,6 +124,11 @@ int main(int argc, char *argv[])
                                           QCoreApplication::translate("main", "file"));
     parser.addOption(writeVbiCsvOption);
 
+    QCommandLineOption writeFfmetadataOption("ffmetadata",
+                                             QCoreApplication::translate("main", "Write navigation information as FFMETADATA1"),
+                                             QCoreApplication::translate("main", "file"));
+    parser.addOption(writeFfmetadataOption);
+
     // -- Positional arguments --
 
     // Positional argument to specify input video file
@@ -167,6 +173,13 @@ int main(int argc, char *argv[])
             return 1;
         }
     }
+    if (parser.isSet(writeFfmetadataOption)) {
+        const QString &fileName = parser.value(writeFfmetadataOption);
+        if (!writeFfmetadata(metaData, fileName)) {
+            qCritical() << "Failed to write output file:" << fileName;
+            return 1;
+        }
+    }
 
     // Quit with success
     return 0;