Dive media: prepare for video-thumbnails

Video thumbnails are more complex than simple picture thumbnails.
We store a duration and might want to store multiple images.

Therefore, refactor the thumbnailing in imagedownloader.cpp. Move
the thumbnail-writing down in the call chain to where the thumbnails
are created, since we have more information there (i.e. whether we
could parse the file but not extract an image, etc.).

Split the write-to-cache function into three versions:
  - pictures
  - videos
  - unknown

Define the video-thumbnail on-disk format as
  - uint32  MEDIATYPE_VIDEO
  - uint32  duration of video in seconds
  - uint32  number of pictures
  for each picture:
	- uint32  offset in msec from begining of video
	- QImage  frame

Currently, we write 0 pictures. This will be filled in subsequent commits.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

2 files changed, 96 insertions, 23 deletions

diff --git a/core/imagedownloader.cpp b/core/imagedownloader.cpp
index 14bde8032..fd155bec6 100644
--- a/core/imagedownloader.cpp
+++ b/core/imagedownloader.cpp
@@ -93,22 +93,31 @@ Thumbnailer::Thumbnail Thumbnailer::fetchImage(const QString &filename, const QS
 		mediatype_t type = get_metadata(qPrintable(filename), &md);
 
 		// For io error or video, return early with the appropriate dummy-icon.
-		if (type == MEDIATYPE_IO_ERROR)
+		if (type == MEDIATYPE_IO_ERROR) {
 			return { failImage, MEDIATYPE_IO_ERROR };
-		else if (type == MEDIATYPE_VIDEO)
+		} else if (type == MEDIATYPE_VIDEO) {
+			addVideoThumbnailToCache(originalFilename, md.duration);
 			return { videoImage, MEDIATYPE_VIDEO };
+		}
 
 		// Try if Qt can parse this image. If it does, use this as a thumbnail.
 		QImage thumb(filename);
-		if (!thumb.isNull())
+		if (!thumb.isNull()) {
+			addPictureThumbnailToCache(originalFilename, thumb);
 			return { thumb, MEDIATYPE_PICTURE };
+		}
 
 		// Neither our code, nor Qt could determine the type of this object from looking at the data.
-		// Try to check for a video-file extension.
-		if (hasVideoFileExtension(filename))
+		// Try to check for a video-file extension. Since we couldn't parse the video file,
+		// we pass 0 as the duration.
+		if (hasVideoFileExtension(filename)) {
+			addVideoThumbnailToCache(originalFilename, {0} );
 			return { videoImage, MEDIATYPE_VIDEO };
+		}
 
 		// Give up: we simply couldn't determine what this thing is.
+		// But since we managed to read this file, mark this file in the cache as unknown.
+		addUnknownThumbnailToCache(originalFilename);
 		return { unknownImage, MEDIATYPE_UNKNOWN };
 	} else if (tryDownload) {
 		// This has to be done in UI main thread, because QNetworkManager refuses
@@ -176,6 +185,37 @@ Thumbnailer *Thumbnailer::instance()
 	return &self;
 }
 
+Thumbnailer::Thumbnail Thumbnailer::getPictureThumbnailFromStream(QDataStream &stream)
+{
+	QImage res;
+	stream >> res;
+	return { res, MEDIATYPE_PICTURE, 0 };
+}
+
+Thumbnailer::Thumbnail Thumbnailer::getVideoThumbnailFromStream(QDataStream &stream)
+{
+	quint32 duration, numPics;
+	stream >> duration >> numPics;
+
+	// If reading did not succeed, schedule for recalculation - this thumbnail might
+	// have been written by an older version, which couldn't extract the duration.
+	if (stream.status() != QDataStream::Ok)
+		return { QImage(), MEDIATYPE_VIDEO, 0 };
+
+	// Currently, we support only one picture
+	QImage res;
+	if (numPics > 0) {
+		quint32 offset;
+		QImage res;
+		stream >> offset >> res;
+	}
+
+	// No picture -> show dummy-icon
+	return { res.isNull() ? videoImage : res, MEDIATYPE_VIDEO, {(int32_t)duration} };
+}
+
+// Fetch a thumbnail from cache.
+// If Thumbnail::QImage is null, the thumbnail is scheduled for recreation.
 Thumbnailer::Thumbnail Thumbnailer::getThumbnailFromCache(const QString &picture_filename)
 {
 	QString filename = thumbnailFileName(picture_filename);
@@ -194,48 +234,78 @@ Thumbnailer::Thumbnail Thumbnailer::getThumbnailFromCache(const QString &picture
 			if (pictureTime.isValid() && thumbnailTime.isValid() && thumbnailTime < pictureTime) {
 				// Both files exist, have valid timestamps and thumbnail was calculated before picture.
 				// Return an empty thumbnail to signal recalculation of the thumbnail
-				return { QImage(), MEDIATYPE_UNKNOWN };
+				return { QImage(), MEDIATYPE_UNKNOWN, 0 };
 			}
 		}
 	}
 
 	if (!file.open(QIODevice::ReadOnly))
-		return { QImage(), MEDIATYPE_UNKNOWN };
+		return { QImage(), MEDIATYPE_UNKNOWN, 0 };
 	QDataStream stream(&file);
 
 	// Each thumbnail file is composed of a media-type and an image file.
 	quint32 type;
 	QImage res;
 	stream >> type;
-	stream >> res;
 
-	// Thumbnails of videos currently not supported - replace by dummy
-	// TODO: Perhaps extract thumbnails
-	if (type == MEDIATYPE_VIDEO)
-		res = videoImage;
-	else if (type == MEDIATYPE_UNKNOWN)
-		res = unknownImage;
+	switch (type) {
+	case MEDIATYPE_PICTURE:	return getPictureThumbnailFromStream(stream);
+	case MEDIATYPE_VIDEO:	return getVideoThumbnailFromStream(stream);
+	case MEDIATYPE_UNKNOWN:	return { unknownImage, MEDIATYPE_UNKNOWN, 0 };
+	default:		return { QImage(), MEDIATYPE_UNKNOWN, 0 };
+	}
+}
+
+void Thumbnailer::addVideoThumbnailToCache(const QString &picture_filename, duration_t duration)
+{
+	// The format of video thumbnails:
+	//	uint32	MEDIATYPE_VIDEO
+	//	uint32	duration of video in seconds
+	//	uint32	number of pictures (0 = we didn't manage to extract a picture)
+	//	for each picture:
+	//		uint32	offset in msec from begining of video
+	//		QImage	frame
+	QString filename = thumbnailFileName(picture_filename);
+	QSaveFile file(filename);
+	if (!file.open(QIODevice::WriteOnly))
+		return;
+	QDataStream stream(&file);
 
-	return { res, (mediatype_t)type };
+	stream << (quint32)MEDIATYPE_VIDEO;
+	stream << (quint32)duration.seconds;
+	stream << (quint32)0;			// Currently, we don't support extraction of images
+	file.commit();
 }
 
-void Thumbnailer::addThumbnailToCache(const Thumbnail &thumbnail, const QString &picture_filename)
+void Thumbnailer::addPictureThumbnailToCache(const QString &picture_filename, const QImage &thumbnail)
 {
-	if (thumbnail.img.isNull())
+	if (thumbnail.isNull())
 		return;
 
+	// The format of a picture-thumbnail is very simple:
+	// 	uint32	MEDIATYPE_PICTURE
+	// 	QImage	thumbnail
 	QString filename = thumbnailFileName(picture_filename);
 	QSaveFile file(filename);
 	if (!file.open(QIODevice::WriteOnly))
 		return;
 	QDataStream stream(&file);
 
-	stream << (quint32)thumbnail.type;
-	if (thumbnail.type == MEDIATYPE_PICTURE) // TODO: Perhaps also support caching of video thumbnails
-		stream << thumbnail.img;
+	stream << (quint32)MEDIATYPE_PICTURE;
+	stream << thumbnail;
 	file.commit();
 }
 
+void Thumbnailer::addUnknownThumbnailToCache(const QString &picture_filename)
+{
+	QString filename = thumbnailFileName(picture_filename);
+	QSaveFile file(filename);
+	if (!file.open(QIODevice::WriteOnly))
+		return;
+	QDataStream stream(&file);
+	stream << (quint32)MEDIATYPE_UNKNOWN;
+}
+
 void Thumbnailer::recalculate(QString filename)
 {
 	Thumbnail thumbnail = getHashedImage(filename, true);
@@ -245,7 +315,6 @@ void Thumbnailer::recalculate(QString filename)
 	// and therefore a "broken" image symbol may be shown.
 	if (thumbnail.type == MEDIATYPE_STILL_LOADING || thumbnail.type == MEDIATYPE_IO_ERROR)
 		return;
-	addThumbnailToCache(thumbnail, filename);
 
 	QMutexLocker l(&lock);
 	emit thumbnailChanged(filename, thumbnail.img);
@@ -266,7 +335,6 @@ void Thumbnailer::processItem(QString filename, bool tryDownload)
 		} else {
 			int size = maxThumbnailSize();
 			thumbnail.img = thumbnail.img.scaled(size, size, Qt::KeepAspectRatio);
-			addThumbnailToCache(thumbnail, filename);
 		}
 	}
 
diff --git a/core/imagedownloader.h b/core/imagedownloader.h
index f89f80678..dcdf08d20 100644
--- a/core/imagedownloader.h
+++ b/core/imagedownloader.h
@@ -52,13 +52,18 @@ private:
 	struct Thumbnail {
 		QImage img;
 		mediatype_t type;
+		duration_t duration;
 	};
 
 	Thumbnailer();
-	static void addThumbnailToCache(const Thumbnail &thumbnail, const QString &picture_filename);
+	static void addPictureThumbnailToCache(const QString &picture_filename, const QImage &thumbnail);
+	static void addVideoThumbnailToCache(const QString &picture_filename, duration_t duration);
+	static void addUnknownThumbnailToCache(const QString &picture_filename);
 	void recalculate(QString filename);
 	void processItem(QString filename, bool tryDownload);
 	Thumbnail getThumbnailFromCache(const QString &picture_filename);
+	Thumbnail getPictureThumbnailFromStream(QDataStream &stream);
+	Thumbnail getVideoThumbnailFromStream(QDataStream &stream);
 	Thumbnail fetchImage(const QString &filename, const QString &originalFilename, bool tryDownload);
 	Thumbnail getHashedImage(const QString &filename, bool tryDownload);