Video derivatives in Hyrax

gistfile1.txt

How are video derivatives done in hyrax?

1. In hyrax app/jobs/create_derivatives_job.rb
it calls:
file_set.create_derivatives(filename)

2. In hyrax app/services/hyrax/file_set_derivatives_service.rb
the create_derivatives method calls:
create_video_derivatives(filename)

3. The create_video_derivatives method calls:
Hydra::Derivatives::VideoDerivatives.create(filename,
  outputs: [
    { label: :thumbnail, format: 'jpg', url: derivative_url('thumbnail') },
    { label: 'webm', format: 'webm', url: derivative_url('webm') },
    { label: 'mp4', format: 'mp4', url: derivative_url('mp4') }
  ])

4. In hydra-derivatives, the VideoDerivatives.create method comes from the Runner superclass:
lib/hydra/derivatives/runners/video_derivatives.rb
it calls:
processor_class.new(f.path,
                    instructions.merge(source_file_service: source_file_service),
                    output_file_service: output_file_service).process
where the processor_class comes from VideoDerivatives, so it will be:
  Processors::Video::Processor
in lib/hydra/derivatives/processors/video/processor.rb, which includes the Ffmpeg module.
The Ffmpeg module includes the ShellBasedProcessor
so the "process" method from above comes from:
  ShellBasedProcessor#process

5. in lib/hydra/derivatives/processors/shell_based_processor.rb
The process method calls:
encode_file(format, options_for(format))

6. The encode_file method calls:
self.class.encode(source_path, options, temp_file_name)
which will be Ffmpeg.encode
which actually calls ffmpeg on the command line

It looks like the actual files are written using these classes:
app/services/hyrax/persist_derivatives.rb
app/services/hyrax/persist_directly_contained_output_file_service.rb