footage: use version number on cache

Will allow us to easily discard cache later

app/node/project/footage/footage.cpp

@@ -90,12 +90,8 @@ void Footage::InputValueChangedEvent(const QString &input, int element)
 
       FootageDescription footage_info;
 
-      if (QFileInfo::exists(meta_cache_file)) {
-
-        // Load meta cache file
-        footage_info.Load(meta_cache_file);
-
-      } else {
+      // Try to load footage info from cache
+      if (!QFileInfo::exists(meta_cache_file) || !footage_info.Load(meta_cache_file)) {
 
         // Probe and create cache
         QVector<DecoderPtr> decoder_list = Decoder::ReceiveListOfAllDecoders();

app/node/project/footage/footagedescription.cpp

@@ -40,6 +40,20 @@ bool FootageDescription::Load(const QString &filename)
 
     while (XMLReadNextStartElement(&reader)) {
       if (reader.name() == QStringLiteral("streamcache")) {
+        // Default to first version of metadata (which wasn't versioned at all)
+        unsigned version = 1;
+
+        XMLAttributeLoop((&reader), attr) {
+          if (attr.name() == QStringLiteral("version")) {
+            version = attr.value().toUInt();
+          }
+        }
+
+        if (version != kFootageMetaVersion) {
+          // If this is a different version, discard so we can probe new data
+          return false;
+        }
+
         while (XMLReadNextStartElement(&reader)) {
           if (reader.name() == QStringLiteral("decoder")) {
             decoder_ = reader.readElementText();
@@ -68,7 +82,11 @@ bool FootageDescription::Load(const QString &filename)
 
     file.close();
 
-    return true;
+    if (reader.hasError()) {
+      qWarning() << "Failed to load footage description for" << filename << reader.errorString();
+    } else {
+      return true;
+    }
   }
 
   return false;
@@ -88,6 +106,8 @@ bool FootageDescription::Save(const QString &filename) const
 
   writer.writeStartElement(QStringLiteral("streamcache"));
 
+  writer.writeAttribute(QStringLiteral("version"), QString::number(kFootageMetaVersion));
+
   writer.writeTextElement(QStringLiteral("decoder"), decoder_);
 
   writer.writeStartElement(QStringLiteral("streams"));

app/node/project/footage/footagedescription.h

@@ -112,6 +112,8 @@ public:
   }
 
 private:
+  static constexpr unsigned kFootageMetaVersion = 1;
+
   QString decoder_;
 
   QVector<VideoParams> video_streams_;