Ogg media container file: Ruby parsing library

Ogg is a popular media container format, which provides basic streaming / buffering mechanisms and is content-agnostic. Most popular codecs that are used within Ogg streams are Vorbis (thus making Ogg/Vorbis streams) and Theora (Ogg/Theora).

Ogg stream is a sequence Ogg pages. They can be read sequentially, or one can jump into arbitrary stream location and scan for "OggS" sync code to find the beginning of a new Ogg page and continue decoding the stream contents from that one.

File extension

["ogg", "ogv", "oga", "spx", "ogx"]

KS implementation details

License: CC0-1.0

References

This page hosts a formal specification of Ogg media container file using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Runtime library

All parsing code for Ruby generated by Kaitai Struct depends on the Ruby runtime library. You have to install it before you can parse data.

The Ruby runtime library can be installed from RubyGems:

gem install kaitai-struct

Code

Parse a local file and get structure in memory:

data = Ogg.from_file("path/to/local/file.["ogg", "ogv", "oga", "spx", "ogx"]")

Or parse structure from a string of bytes:

bytes = "\x00\x01\x02..."
data = Ogg.new(Kaitai::Struct::Stream.new(bytes))

After that, one can get various attributes from the structure by invoking getter methods like:

data.pages # => get pages

Ruby source code to parse Ogg media container file

ogg.rb

# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

require 'kaitai/struct/struct'

unless Gem::Version.new(Kaitai::Struct::VERSION) >= Gem::Version.new('0.9')
  raise "Incompatible Kaitai Struct Ruby API: 0.9 or later is required, but you have #{Kaitai::Struct::VERSION}"
end


##
# Ogg is a popular media container format, which provides basic
# streaming / buffering mechanisms and is content-agnostic. Most
# popular codecs that are used within Ogg streams are Vorbis (thus
# making Ogg/Vorbis streams) and Theora (Ogg/Theora).
# 
# Ogg stream is a sequence Ogg pages. They can be read sequentially,
# or one can jump into arbitrary stream location and scan for "OggS"
# sync code to find the beginning of a new Ogg page and continue
# decoding the stream contents from that one.
class Ogg < Kaitai::Struct::Struct
  def initialize(_io, _parent = nil, _root = self)
    super(_io, _parent, _root)
    _read
  end

  def _read
    @pages = []
    i = 0
    while not @_io.eof?
      @pages << Page.new(@_io, self, @_root)
      i += 1
    end
    self
  end

  ##
  # Ogg page is a basic unit of data in an Ogg bitstream, usually
  # it's around 4-8 KB, with a maximum size of 65307 bytes.
  class Page < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @sync_code = @_io.read_bytes(4)
      raise Kaitai::Struct::ValidationNotEqualError.new([79, 103, 103, 83].pack('C*'), sync_code, _io, "/types/page/seq/0") if not sync_code == [79, 103, 103, 83].pack('C*')
      @version = @_io.read_bytes(1)
      raise Kaitai::Struct::ValidationNotEqualError.new([0].pack('C*'), version, _io, "/types/page/seq/1") if not version == [0].pack('C*')
      @reserved1 = @_io.read_bits_int_be(5)
      @is_end_of_stream = @_io.read_bits_int_be(1) != 0
      @is_beginning_of_stream = @_io.read_bits_int_be(1) != 0
      @is_continuation = @_io.read_bits_int_be(1) != 0
      @_io.align_to_byte
      @granule_pos = @_io.read_u8le
      @bitstream_serial = @_io.read_u4le
      @page_seq_num = @_io.read_u4le
      @crc32 = @_io.read_u4le
      @num_segments = @_io.read_u1
      @len_segments = Array.new(num_segments)
      (num_segments).times { |i|
        @len_segments[i] = @_io.read_u1
      }
      @segments = Array.new(num_segments)
      (num_segments).times { |i|
        @segments[i] = @_io.read_bytes(len_segments[i])
      }
      self
    end
    attr_reader :sync_code

    ##
    # Version of the Ogg bitstream format. Currently must be 0.
    attr_reader :version
    attr_reader :reserved1

    ##
    # EOS (End Of Stream) mark. This page is the last page in the
    # logical bitstream. The EOS flag must be set on the final page of
    # every logical bitstream, and must not be set on any other page.
    attr_reader :is_end_of_stream

    ##
    # BOS (Beginning Of Stream) mark. This page is the first page in
    # the logical bitstream. The BOS flag must be set on the first
    # page of every logical bitstream, and must not be set on any
    # other page.
    attr_reader :is_beginning_of_stream

    ##
    # The first packet on this page is a continuation of the previous
    # packet in the logical bitstream.
    attr_reader :is_continuation

    ##
    # "Granule position" is the time marker in Ogg files. It is an
    # abstract value, whose meaning is determined by the codec. It
    # may, for example, be a count of the number of samples, the
    # number of frames or a more complex scheme.
    attr_reader :granule_pos

    ##
    # Serial number that identifies a page as belonging to a
    # particular logical bitstream. Each logical bitstream in a file
    # has a unique value, and this field allows implementations to
    # deliver the pages to the appropriate decoder. In a typical
    # Vorbis and Theora file, one stream is the audio (Vorbis), and
    # the other is the video (Theora).
    attr_reader :bitstream_serial

    ##
    # Sequential number of page, guaranteed to be monotonically
    # increasing for each logical bitstream. The first page is 0, the
    # second 1, etc. This allows implementations to detect when data
    # has been lost.
    attr_reader :page_seq_num

    ##
    # This field provides a CRC32 checksum of the data in the entire
    # page (including the page header, calculated with the checksum
    # field set to 0). This allows verification that the data has not
    # been corrupted since it was created. Pages that fail the
    # checksum should be discarded. The checksum is generated using a
    # polynomial value of 0x04C11DB7.
    attr_reader :crc32

    ##
    # The number of segments that exist in this page. There can be a
    # maximum of 255 segments in any one page.
    attr_reader :num_segments

    ##
    # Table of lengths of segments.
    attr_reader :len_segments

    ##
    # Segment content bytes make up the rest of the Ogg page.
    attr_reader :segments
  end
  attr_reader :pages
end