hydra-derivatives

Derivative generation for hydra

If you have an ActiveFedora class like this:

    class GenericFile < ActiveFedora::Base
        include Hydra::Derivatives

        contains 'content'
        attr_accessor :mime_type

        # Use a block to declare which derivatives you want to generate

        def create_derivatives(filename)
          case mime_type
          when 'application/pdf'
            PdfDerivatives.create(filename, outputs: [{ label: :thumb, size: "100x100>" }]
          when 'audio/wav'
            AudioDerivatives.create(self, source: :original_file, outputs: [{ label: :mp3, format: 'mp3', url: "#{uri}/mp3" }, { label: :ogg, format: 'ogg', url: "#{uri}/ogg" }])
          when 'video/avi'
            VideoDerivatives.create(filename, outputs: [{ label: :mp4, format: 'mp4'}, { label: :webm, format: 'webm'}])
          when 'image/png', 'image/jpg'
            ImageDerivatives.create(self, source: :original_file,
                                    outputs: [
                                      { label: :medium, size: "300x300>", url: "#{uri}/medium" },
                                      { label: :thumb, size: "100x100>", url: "#{uri}/thumb" }])
          when 'application/vnd.ms-powerpoint'
            DocumentDerivatives.create(filename, outputs[{ label: :preservation, format: 'pptx' }, { label: :access, format: 'pdf' }, { label: :thumnail, format: 'jpg' })
          when 'image/tiff'
            Jpeg2kDerivatives.create(filename, outputs: [{ label: :service, resize: "3600x3600>" }])
          end
        end
    end

And you add some content to it:

   obj = GenericFile.new
   obj.original_file.content = File.open(...)
   obj.mime_type = 'image/jpg'
   obj.save

Then when you call obj.create_derivatives two new files, 'thumbnail' and 'content_medium', will have been created with downsized images in them.

We recommend you run obj.create_derivatives in a background worker, because some derivative creation (especially videos) can take a long time.

Configuration

Retrieving from a basic container in Fedora

Provide the object and :source option instead of a filename

PdfDerivatives.create(active_fedora_object, source: :original_file, outputs: [{ label: :thumb, size: "100x100>" }]

Processing Timeouts

hydra-derivatives can be configured to timeout derivatives processes. Each process type has a separate timeout. If no timeout is set the system will process until complete (possibly indefinitely).

require 'hydra/derivatives'

Hydra::Derivatives::Video::Processor.timeout  = 10.minutes
Hydra::Derivatives::Document.timeout = 5.minutes
Hydra::Derivatives::Audio.timeout = 10.minutes
Hydra::Derivatives::Image.timeout = 5.minutes

Video Processing configuration

Flags can be set for using different video codes. Default codecs are shown below

Hydra::Derivatives::Video::Processor.config.mpeg4.codec = '-vcodec libx264 -acodec libfdk_aac'
Hydra::Derivatives::Video::Processor.config.webm.codec = '-vcodec libvpx -acodec libvorbis'
Hydra::Derivatives::Video::Processor.config.mkv.codec = '-vcodec ffv1'
Hydra::Derivatives::Video::Processor.config.jpeg.codec = '-vcodec mjpeg'

Installation

Just add gem 'hydra-derivatives' to your Gemfile.

Dependencies

• FITS - version 0.6.2
• FFMpeg
• LibreOffice (openoffice.org-headless on Ubuntu/Debian to avoid "X11 error: Can't open display:")
• ImageMagick
• Kakadu's kdu_compress (optional)

To enable LibreOffice, FFMpeg, ImageMagick, FITS support, and kdu_compress support, make sure they are on your path. Most people will put that in their .bash_profile or somewhere similar.

For example:

# in .bash_profile
export PATH=${PATH}:/Users/justin/workspace/fits-0.6.2:/Applications/LibreOffice.app/Contents/MacOS

Alternatively, you can configure their paths:

Hydra::Derivatives.ffmpeg_path = '/opt/local/ffmpeg/bin/ffmpeg'
Hydra::Derivatives.fits_path = '/opt/local/fits/bin/fits.sh'
Hydra::Derivatives.libreoffice_path = '/opt/local/libreoffice_path/bin/soffice'
Hydra::Derivatives.kdu_compress_path = '/usr/local/bin/kdu_compress'

JPEG2k Directives

Unlike the other processors, the Jpeg2kImage processor does not generally accept arguments that directly (or nearly so) translate to the arguments you would give to the corresponding command line utility.

Instead, each directive may contain these arguments:

• :output_path (String) : The name for the new file
• :to_srgb (Boolean) : If true and the image is a color image it will map the source image color profile to sRGB. Default: true
• :resize (String) : Geometry; the same syntax as the Hydra::Derivatives::Image processor
• :recipe :
  • If a Symbol the recipe will be read from the Hydra::Derivatives.kdu_compress_recipes hash. You can override this, or a couple of samples are supplied. The symbol in the config file should be the name in the model + _{quality}, e.g. recipe: :default will look :default_color or :default_grey in the hash.
  • If a String the recipe in the string will be used. You may include anything the command line utility will accept except -i or -o. See $ kdu_compress -usage in your shell.
  • If no :recipe is provided the processor will examine the image and make a best guess, but you can set a few basic options (the remainder of this list). Note that these are ignored if you provided a recipe via either of the first two methods described.
• :levels (Integer) : The number of decomposition levels. The default is the number of times the long dimension can be divided by two, down to 96, e.g. a 7200 pixel image would have 6 levels (3600, 1800, 900, 450, 225, 112)
• :layers (Integer) : The number of quality layers. Default: 8
• :compression (Integer) : The left number of the compression ratio n:1, e.g. 12 will apply 12:1 compression. Default: 10.
• :tile_size (Integer) : Pixel dimension of the tiles. Default: 1024