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MediaFilters: Transforming DSpace Content

Overview

DSpace can apply filters or transformations to files/bitstreams, creating new content. Filters are included that extract text for full-text searching, and create thumbnails for items that contain images. The media filters are controlled by the dspace filter-media script which traverses the asset store, invoking all configured MediaFilter or FormatFilter classes on files/bitstreams (see Configuring Media Filters for more information on how they are configured).

Available Media Filters

Below is a listing of all currently available Media Filters, and what they actually do:

Name

Java Class

Function

Enabled by Default?

HTML Text Extractor

org.dspace.app.mediafilter.HTMLFilter

extracts the full text of HTML documents for full text indexing. (Uses Swing's HTML Parser)

true

JPEG Thumbnail

org.dspace.app.mediafilter.JPEGFilter

creates thumbnail images of GIF, JPEG and PNG files

true

Branded Preview JPEG

org.dspace.app.mediafilter.BrandedPreviewJPEGFilter

creates a branded preview image for GIF, JPEG and PNG files

false

PDF Text Extractor

org.dspace.app.mediafilter.PDFFilter

extracts the full text of Adobe PDF documents (only if text-based or OCRed) for full text indexing. (Uses the Apache PDFBox tool)

true

XPDF Text Extractor

org.dspace.app.mediafilter.XPDF2Text

extracts the full text of Adobe PDF documents (only if text-based or OCRed) for full text indexing (Uses the XPDF command line tools available for Unix.) See XPDF Filter Configuration for details on installing/enabling.

false

Word Text Extractor

org.dspace.app.mediafilter.WordFilter

extracts the full text of Microsoft Word or Plain Text documents for full text indexing. (Uses the "Microsoft Word Text Mining" tools.)

true

PowerPoint Text Extractor

org.dspace.app.mediafilter.PowerPointFilter

extracts the full text of slides and notes in Microsoft PowerPoint and PowerPoint XML documents for full text indexing (Uses the Apache POI tools.)

true

Please note that the filter-media script will automatically update the DSpace search index by default (see ReIndexing Content (for Browse or Search)) This is the recommended way to run these scripts. But, should you wish to disable it, you can pass the -n flag to either script to do so (see Executing (via Command Line) below).

Enabling/Disabling MediaFilters

The media filter plugin configuration filter.plugins in dspace.cfg contains a list of all enabled media/format filter plugins (see Configuring Media Filters for more information). By modifying the value of filter.plugins you can disable or enable MediaFilter plugins.

Executing (via Command Line)

The media filter system is intended to be run from the command line (or regularly as a cron task):

With no options, this traverses the asset store, applying media filters to bitstreams, and skipping bitstreams that have already been filtered.

Available Command-Line Options:

  • Help : [dspace]/bin/dspace filter-media -h
    • Display help message describing all command-line options.
  • Force mode : [dspace]/bin/dspace filter-media -f
    • Apply filters to ALL bitstreams, even if they've already been filtered. If they've already been filtered, the previously filtered content is overwritten.
  • Identifier mode : [dspace]/bin/dspace filter-media -i 123456789/2
    • Restrict processing to the community, collection, or item named by the identifier - by default, all bitstreams of all items in the repository are processed. The identifier must be a Handle, not a DB key. This option may be combined with any other option.
  • Maximum mode : [dspace]/bin/dspace filter-media -m 1000
    • Suspend operation after the specified maximum number of items have been processed - by default, no limit exists. This option may be combined with any other option.
  • No-Index mode : [dspace]/bin/dspace filter-media -n
    • Suppress index creation - by default, a new search index is created for full-text searching. This option suppresses index creation if you intend to run index-update elsewhere.
  • Plugin mode : [dspace]/bin/dspace filter-media -p "PDF Text Extractor","Word Text Extractor"
    • Apply ONLY the filter plugin(s) listed (separated by commas). By default all named filters listed in the filter.plugins field of dspace.cfg are applied. This option may be combined with any other option. WARNING: multiple plugin names must be separated by a comma (i.e. ',') and NOT a comma followed by a space (i.e. ', ').
  • Skip mode : [dspace]/bin/dspace filter-media -s 123456789/9,123456789/100
    • SKIP the listed identifiers (separated by commas) during processing. The identifiers must be Handles (not DB Keys). They may refer to items, collections or communities which should be skipped. This option may be combined with any other option. WARNING: multiple identifiers must be separated by a comma (i.e. ',') and NOT a comma followed by a space (i.e. ', ').
    • NOTE: If you have a large number of identifiers to skip, you may maintain this comma-separated list within a separate file (e.g. filter-skiplist.txt). Use the following format to call the program. Please note the use of the "grave" or "tick" (`) symbol and do not use the single quotation.
      • [dspace]/bin/dspace filter-media -s `less filter-skiplist.txt`
  • Verbose mode : [dspace]/bin/dspace filter-media -v
    • Verbose mode - print all extracted text and other filter details to STDOUT.
      Adding your own filters is done by creating a class which implements the org.dspace.app.mediafilter.FormatFilter interface. See the Creating a new Media/Format Filter topic and comments in the source file FormatFilter.java for more information. In theory filters could be implemented in any programming language (C, Perl, etc.) However, they need to be invoked by the Java code in the Media Filter class that you create.

Creating Custom MediaFilters

Creating a simple Media Filter

New Media Filters must implement the org.dspace.app.mediafilter.FormatFilter interface. More information on the methods you need to implement is provided in the FormatFilter.java source file. For example:

public class MySimpleMediaFilter implements FormatFilter

Alternatively, you could extend the org.dspace.app.mediafilter.MediaFilter class, which just defaults to performing no pre/post-processing of bitstreams before or after filtering.

public class MySimpleMediaFilter extends MediaFilter

You must give your new filter a "name", by adding it and its name to the plugin.named.org.dspace.app.mediafilter.FormatFilter field in dspace.cfg. In addition to naming your filter, make sure to specify its input formats in the filter.<class path>.inputFormats config item. Note the input formats must match the short description field in the Bitstream Format Registry (i.e. bitstreamformatregistry table).

If you neglect to define the inputFormats for a particular filter, the MediaFilterManager will never call that filter, since it will never find a bitstream which has a format matching that filter's input format(s).

If you have a complex Media Filter class, which actually performs different filtering for different formats (e.g. conversion from Word to PDF and conversion from Excel to CSV), you should define this as described in Chapter 13.3.2.2 .

Creating a Dynamic or "Self-Named" Format Filter

If you have a more complex Media/Format Filter, which actually performs multiple filtering or conversions for different formats (e.g. conversion from Word to PDF and conversion from Excel to CSV), you should have define a class which implements the FormatFilter interface, while also extending the Chapter 13.3.2.2 SelfNamedPlugin class. For example:

public class MyComplexMediaFilter extends SelfNamedPlugin implements FormatFilter

Since SelfNamedPlugins are self-named (as stated), they must provide the various names the plugin uses by defining a getPluginNames() method. Generally speaking, each "name" the plugin uses should correspond to a different type of filter it implements (e.g. "Word2PDF" and "Excel2CSV" are two good names for a complex media filter which performs both Word to PDF and Excel to CSV conversions).

Self-Named Media/Format Filters are also configured differently in dspace.cfg. Below is a general template for a Self Named Filter (defined by an imaginary MyComplexMediaFilter class, which can perform both Word to PDF and Excel to CSV conversions):

As shown above, each Self-Named Filter class must be listed in the plugin.selfnamed.org.dspace.app.mediafilter.FormatFilter item in dspace.cfg. In addition, each Self-Named Filter must define the input formats for each named plugin defined by that filter. In the above example the MyComplexMediaFilter class is assumed to have defined two named plugins, Word2PDF and Excel2CSV. So, these two valid plugin names ("Word2PDF" and "Excel2CSV") must be returned by the getPluginNames() method of the MyComplexMediaFilter class.

These named plugins take different input formats as defined above (see the corresponding inputFormats setting).

If you neglect to define the inputFormats for a particular named plugin, the MediaFilterManager will never call that plugin, since it will never find a bitstream which has a format matching that plugin's input format(s).

For a particular Self-Named Filter, you are also welcome to define additional configuration settings in dspace.cfg. To continue with our current example, each of our imaginary plugins actually results in a different output format (Word2PDF creates "Adobe PDF", while Excel2CSV creates "Comma Separated Values"). To allow this complex Media Filter to be even more configurable (especially across institutions, with potential different "Bitstream Format Registries"), you may wish to allow for the output format to be customizable for each named plugin. For example:

Any custom configuration fields in dspace.cfg defined by your filter are ignored by the MediaFilterManager, so it is up to your custom media filter class to read those configurations and apply them as necessary. For example, you could use the following sample Java code in your MyComplexMediaFilter class to read these custom outputFormat configurations from dspace.cfg:

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