Class: Kithe::FfmpegTransformer

Inherits:
Object
  • Object
show all
Defined in:
app/derivative_transformers/kithe/ffmpeg_transformer.rb

Instance Method Summary collapse

Constructor Details

#initialize(output_suffix:, bitrate: nil, force_mono: false, audio_codec: nil, other_ffmpeg_args: nil) ⇒ FfmpegTransformer

Specifies the most important args to send to ffmpeg for creating audio and video derivatives.



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# File 'app/derivative_transformers/kithe/ffmpeg_transformer.rb', line 14

def initialize(output_suffix:, bitrate:nil, force_mono:false, audio_codec:nil, other_ffmpeg_args:nil)
  @output_suffix, @bitrate, @force_mono, @audio_codec, @other_ffmpeg_args =
   output_suffix,  bitrate,  force_mono,  audio_codec,  other_ffmpeg_args

  # Default settings:
  @audio_codec ||= 'libopus' if output_suffix == 'webm'

  # Validation:
  if other_ffmpeg_args && other_ffmpeg_args.class != Array
    raise ArgumentError.new('If "other_ffmpeg_args" is not nil, it needs to be an array of strings.')
  end
  if bitrate && !/\d+k/.match(bitrate)
    raise ArgumentError.new('If "bitrate" is not nil, it needs to be a string like "64k" or "128k".')
  end
end

Instance Method Details

#call(original_file) ⇒ Object

Will raise TTY::Command::ExitError if the ffmpeg returns non-null.



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# File 'app/derivative_transformers/kithe/ffmpeg_transformer.rb', line 42

def call(original_file)
  tempfile = Tempfile.new(['temp_deriv', ".#{@output_suffix}"])
  # -y tells ffmpeg to overwrite the abovementioned tempfile (still empty)
  # with the output of ffmpeg.
  ffmpeg_args =  [ffmpeg_command, "-y", "-i", original_file.path]
  ffmpeg_args += transform_arguments + [tempfile.path]
  TTY::Command.new(printer: :null).run(*ffmpeg_args)
  return tempfile
end

#transform_arguments ⇒ Object

These are the arguments that specify the nature of the derivative transformation (rather than those specifying input and output files, which are in the call method.



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# File 'app/derivative_transformers/kithe/ffmpeg_transformer.rb', line 32

def transform_arguments
  result  = []
  result += ["-ac", "1"] if @force_mono
  result += ["-codec:a", @audio_codec] if @audio_codec
  result += ["-b:a", @bitrate] if @bitrate
  result += @other_ffmpeg_args if @other_ffmpeg_args
  result
end