footage: merge video and image streams and improve image sequence import process

Image streams were initially separated from video streams, but they're now
joined with a parameter defining if they're a still image, image sequence,
or regular video. The image sequence import process has also improved so
that if images from the same sequence are imported too, they'll either be
ignored or the user won't be asked again for those if they should be an
image sequence (fixes #1193). Also shifts decoder "probe" process to return
an item, useful if the decoder returns a non-footage item.

app/codec/otio/otiodecoder.cpp

@@ -20,6 +20,8 @@
 
 #include "otiodecoder.h"
 
+#include <opentimelineio/timeline.h>
+
 OLIVE_NAMESPACE_ENTER
 
 OTIODecoder::OTIODecoder()
@@ -32,9 +34,21 @@ QString OTIODecoder::id()
   return QStringLiteral("otio");
 }
 
-bool OTIODecoder::Probe(Footage* f, const QAtomicInt* cancelled)
+ItemPtr OTIODecoder::Probe(const QString& filename, const QAtomicInt* cancelled) const
 {
-  return false;
+  if (filename.endsWith(QStringLiteral(".otio"), Qt::CaseInsensitive)) {
+    opentimelineio::v1_0::ErrorStatus es;
+
+    auto timeline = static_cast<opentimelineio::v1_0::Timeline*>(opentimelineio::v1_0::SerializableObjectWithMetadata::from_json_file(filename.toStdString(), &es));
+
+    if (es != opentimelineio::v1_0::ErrorStatus::OK) {
+      return nullptr;
+    }
+
+    qDebug() << "Found" << timeline->video_tracks().size() << "video tracks";
+  }
+
+  return nullptr;
 }
 
 OLIVE_NAMESPACE_EXIT