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Description
The libtracker-extract library is the foundation for Tracker metadata extraction of embedded data in files.
Tracker comes with extractors written for the most common file types (like MP3, JPEG, PNG, etc.), however, for more special cases, 3rd party applications may want to write their own plugin to extract their own file formats. This documentation describes how to do that.
Example 1. Basic extractor example
G_MODULE_EXPORT gboolean
tracker_extract_get_metadata (TrackerExtractInfo *info)
{
GFile *file;
TrackerSparqlBuilder *metadata;
gint height, width;
file = tracker_extract_info_get_file (info);
metadata = tracker_extract_info_get_metadata_builder (info);
/* Do data extraction. */
height = ...
width = ...
/* Insert data into TrackerSparqlBuilder object. */
tracker_sparql_builder_predicate (metadata, "a");
tracker_sparql_builder_object (metadata, "nfo:Image");
tracker_sparql_builder_object (metadata, "nmm:Photo");
tracker_sparql_builder_predicate (metadata, "nfo:width");
tracker_sparql_builder_object_int64 (metadata, width);
tracker_sparql_builder_predicate (metadata, "nfo:height");
tracker_sparql_builder_object_int64 (metadata, height);
/* Were we successful or not? */
return TRUE;
}
NOTE: This example has changed subtly since 0.10. For details see
tracker_extract_get_metadata().
Functions
tracker_extract_get_metadata ()
gboolean
tracker_extract_get_metadata (TrackerExtractInfo *info);
This function must be provided by ALL extractors. This is merely the declaration of the function which must be written by each extractor.
This is checked by tracker-extract by looking up the symbols for each started plugin and making sure this function exists.
The info
parameter contains required information for the
extraction and a location to store the results. The
tracker_extract_info_get_metadata_builder() function returns a
TrackerSparqlBuilder constructed through
tracker_sparql_builder_new_embedded_insert(). The subject
is already set to be the file URN, so implementations of this
function should just provide predicate/object(s) pairs. The
triples contained in this object at the end of the function will be
merged with further file information from miners.
Whenever any of the inserted triples rely on entities that
should also be provided by this extractor (for example, album
or artist information from a song), such insertions should be
added to the preupdate object returned by
tracker_extract_info_get_preupdate_builder(). This is a
TrackerSparqlBuilder created through
tracker_sparql_builder_new_update().
NOTE: If upgrading from 0.10, this function replaces the old
function named tracker_extract_get_data() and has a few subtle
differences. First, there is a return value for success and the
parameters are contained in info
instead of being passed
individually. Second, the extractor is passed the detected
MIME type of the file being extracted.
Since 0.12