Class: FilesHunter::Decoders::OGG

Inherits:
BeginPatternDecoder show all
Defined in:
lib/fileshunter/Decoders/OGG.rb

Constant Summary collapse

BEGIN_PATTERN_OGG = 
"OggS\x00".force_encoding(Encoding::ASCII_8BIT)
KNOWN_EXTENSIONS =

Sorted by the least dominating extension first

{
  'vorbis'.force_encoding(Encoding::ASCII_8BIT) => :oga,
  'theora'.force_encoding(Encoding::ASCII_8BIT) => :ogv
}

Instance Method Summary collapse

Methods inherited from BeginPatternDecoder

#find_segments

Methods inherited from FilesHunter::Decoder

#segments_found, #setup

Instance Method Details

#decode(offset) ⇒ Object 



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# File 'lib/fileshunter/Decoders/OGG.rb', line 19

def decode(offset)
  ending_offset = nil

  cursor = offset
  extensions = [ :ogg, :ogx ] # By default

  nbr_pages = 0
  bitstreams = []
  while (ending_offset == nil)
    #version = @data[cursor+4].ord

    header_type = @data[cursor+5].ord
    invalid_data("@#{cursor} - Invalid header type: #{header_type}") if (header_type > 7)
    #granule_position = @data[cursor+6..cursor+13]

    bitstream_sn = BinData::Uint32le.read(@data[cursor+14..cursor+17])
    page_sequence_idx = BinData::Uint32le.read(@data[cursor+18..cursor+21])
    #checksum = @data[cursor+22..cursor+25]

    # Read the number of segments

    nbr_segments = @data[cursor+26].ord
    # Compute the total size of the payload

    size = 0
    @data[cursor+27..cursor+26+nbr_segments].bytes.each do |segment_size|
      size += segment_size
    end
    log_debug("@#{cursor} - [ Bitstream ##{bitstream_sn} / Page ##{page_sequence_idx} ]: Type #{header_type}, having #{nbr_segments} (total size of #{size})")
    cursor += 27 + nbr_segments
    found_relevant_data(extensions)
    if ((header_type & 0b00000010) != 0)
      # Page of type BOS: Beginning of Stream

      invalid_data("@#{cursor} - Stream #{bitstream_sn} was already marked as begun.") if (bitstreams.include?(bitstream_sn))
      # We can find whether it is a video file or an audio one

      KNOWN_EXTENSIONS.each do |token, extension|
        extensions.unshift(extension) if (@data[cursor..cursor+size-1].index(token) != nil)
        extensions.delete(:oga) if (extensions.include?(:ogv))
        found_relevant_data(extensions)
      end
      bitstreams << bitstream_sn
    elsif ((header_type & 0b00000100) == 0)
      # This is a packet in the middle of a stream

      missing_previous_data if (!bitstreams.include?(bitstream_sn))
      #invalid_data("@#{cursor} - Stream #{bitstream_sn} has not been declared previously.") if (!bitstreams.include?(bitstream_sn))

    end
    cursor += size
    progress(cursor)
    nbr_pages += 1
    # Check if a subsequent page is present

    ending_offset = cursor if ((cursor == @end_offset) or (@data[cursor..cursor+4] != BEGIN_PATTERN_OGG))
  end
  metadata( :nbr_pages => nbr_pages )

  return ending_offset
end

#get_begin_pattern ⇒ Object 



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# File 'lib/fileshunter/Decoders/OGG.rb', line 15

def get_begin_pattern
  return BEGIN_PATTERN_OGG, { :offset_inc => 5 }
end