This page hosts a formal specification of WebP using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All Ruby code generated by Kaitai Struct depends on the Kaitai Struct runtime library for Ruby. You must add this dependency to your project before you can parse or serialize any data.
The Ruby runtime library can be installed from RubyGems:
gem install kaitai-structParse a local file and get structure in memory:
data = Webp.from_file("path/to/local/file.webp")
Or parse structure from a string of bytes:
bytes = "\x00\x01\x02..."
data = Webp.new(Kaitai::Struct::Stream.new(bytes))
After that, one can get various attributes from the structure by invoking getter methods like:
data.magic # => get magic
# 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('0.11')
raise "Incompatible Kaitai Struct Ruby API: 0.11 or later is required, but you have #{Kaitai::Struct::VERSION}"
end
##
# @see https://developers.google.com/speed/webp/docs/riff_container Source
class Webp < Kaitai::Struct::Struct
CHUNK_NAMES = {
5262680 => :chunk_names_xmp_var,
540561494 => :chunk_names_vp8,
542133592 => :chunk_names_xmp,
1179211845 => :chunk_names_exif,
1179471425 => :chunk_names_anmf,
1213221953 => :chunk_names_alph,
1278758998 => :chunk_names_vp8l,
1296519750 => :chunk_names_frgm,
1296649793 => :chunk_names_anim,
1346585417 => :chunk_names_iccp,
1480085590 => :chunk_names_vp8x,
}
I__CHUNK_NAMES = CHUNK_NAMES.invert
COMPRESSION_METHOD = {
0 => :compression_method_none,
1 => :compression_method_webp_lossless,
}
I__COMPRESSION_METHOD = COMPRESSION_METHOD.invert
FILTERING_METHOD = {
0 => :filtering_method_none,
1 => :filtering_method_horizontal,
2 => :filtering_method_vertical,
3 => :filtering_method_gradient,
}
I__FILTERING_METHOD = FILTERING_METHOD.invert
PREPROCESSING = {
0 => :preprocessing_none,
1 => :preprocessing_level_reduction,
}
I__PREPROCESSING = PREPROCESSING.invert
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root || self)
_read
end
def _read
@magic = @_io.read_bytes(4)
raise Kaitai::Struct::ValidationNotEqualError.new([82, 73, 70, 70].pack('C*'), @magic, @_io, "/seq/0") if not @magic == [82, 73, 70, 70].pack('C*')
@len_data = @_io.read_u4le
@webp = @_io.read_bytes(4)
raise Kaitai::Struct::ValidationNotEqualError.new([87, 69, 66, 80].pack('C*'), @webp, @_io, "/seq/2") if not @webp == [87, 69, 66, 80].pack('C*')
_io_payload = @_io.substream(len_data - 4)
@payload = Chunks.new(_io_payload, self, @_root)
self
end
class Alph < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root)
_read
end
def _read
@reserved = @_io.read_bits_int_be(2)
raise Kaitai::Struct::ValidationNotEqualError.new(0, @reserved, @_io, "/types/alph/seq/0") if not @reserved == 0
@preprocessing = Kaitai::Struct::Stream::resolve_enum(Webp::PREPROCESSING, @_io.read_bits_int_be(2))
raise Kaitai::Struct::ValidationNotInEnumError.new(@preprocessing, @_io, "/types/alph/seq/1") if not Webp::I__PREPROCESSING.key?(@preprocessing)
@filtering = Kaitai::Struct::Stream::resolve_enum(Webp::FILTERING_METHOD, @_io.read_bits_int_be(2))
@compression = Kaitai::Struct::Stream::resolve_enum(Webp::COMPRESSION_METHOD, @_io.read_bits_int_be(2))
raise Kaitai::Struct::ValidationNotInEnumError.new(@compression, @_io, "/types/alph/seq/3") if not Webp::I__COMPRESSION_METHOD.key?(@compression)
@_io.align_to_byte
@data = @_io.read_bytes_full
self
end
attr_reader :reserved
attr_reader :preprocessing
attr_reader :filtering
attr_reader :compression
attr_reader :data
end
##
# @see https://developers.google.com/speed/webp/docs/riff_container#animation Source
class Anim < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root)
_read
end
def _read
@background_color = BgColor.new(@_io, self, @_root)
@loop_count = @_io.read_u2le
self
end
class BgColor < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root)
_read
end
def _read
@blue = @_io.read_u1
@green = @_io.read_u1
@red = @_io.read_u1
@alpha = @_io.read_u1
self
end
attr_reader :blue
attr_reader :green
attr_reader :red
attr_reader :alpha
end
attr_reader :background_color
attr_reader :loop_count
end
class Anmf < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root)
_read
end
def _read
@frame_x_div_2 = @_io.read_bits_int_le(24)
@frame_y_div_2 = @_io.read_bits_int_le(24)
@frame_width_minus_1 = @_io.read_bits_int_le(24)
@frame_height_minus_1 = @_io.read_bits_int_le(24)
@duration = @_io.read_bits_int_le(24)
@reserved = @_io.read_bits_int_be(6)
raise Kaitai::Struct::ValidationNotEqualError.new(0, @reserved, @_io, "/types/anmf/seq/5") if not @reserved == 0
@blending_method = @_io.read_bits_int_be(1) != 0
@disposal_method = @_io.read_bits_int_be(1) != 0
@_io.align_to_byte
@data = @_io.read_bytes_full
self
end
def frame_height
return @frame_height unless @frame_height.nil?
@frame_height = frame_height_minus_1 + 1
@frame_height
end
def frame_width
return @frame_width unless @frame_width.nil?
@frame_width = frame_width_minus_1 + 1
@frame_width
end
def frame_x
return @frame_x unless @frame_x.nil?
@frame_x = frame_x_div_2 * 2
@frame_x
end
def frame_y
return @frame_y unless @frame_y.nil?
@frame_y = frame_y_div_2 * 2
@frame_y
end
attr_reader :frame_x_div_2
attr_reader :frame_y_div_2
attr_reader :frame_width_minus_1
attr_reader :frame_height_minus_1
attr_reader :duration
attr_reader :reserved
attr_reader :blending_method
attr_reader :disposal_method
attr_reader :data
end
class Chunk < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root)
_read
end
def _read
@name = Kaitai::Struct::Stream::resolve_enum(Webp::CHUNK_NAMES, @_io.read_u4le)
raise Kaitai::Struct::ValidationNotInEnumError.new(@name, @_io, "/types/chunk/seq/0") if not Webp::I__CHUNK_NAMES.key?(@name)
@len_data = @_io.read_u4le
case name
when :chunk_names_alph
_io_data = @_io.substream(len_data)
@data = Alph.new(_io_data, self, @_root)
when :chunk_names_anim
_io_data = @_io.substream(len_data)
@data = Anim.new(_io_data, self, @_root)
when :chunk_names_anmf
_io_data = @_io.substream(len_data)
@data = Anmf.new(_io_data, self, @_root)
when :chunk_names_vp8
_io_data = @_io.substream(len_data)
@data = Vp8.new(_io_data, self, @_root)
when :chunk_names_vp8l
_io_data = @_io.substream(len_data)
@data = Vp8l.new(_io_data, self, @_root)
when :chunk_names_vp8x
_io_data = @_io.substream(len_data)
@data = Vp8x.new(_io_data, self, @_root)
when :chunk_names_xmp
_io_data = @_io.substream(len_data)
@data = Xmp.new(_io_data, self, @_root)
when :chunk_names_xmp_var
_io_data = @_io.substream(len_data)
@data = Xmp.new(_io_data, self, @_root)
else
@data = @_io.read_bytes(len_data)
end
if len_data % 2 != 0
@padding = @_io.read_bytes(1)
raise Kaitai::Struct::ValidationNotEqualError.new([0].pack('C*'), @padding, @_io, "/types/chunk/seq/3") if not @padding == [0].pack('C*')
end
self
end
attr_reader :name
attr_reader :len_data
attr_reader :data
attr_reader :padding
attr_reader :_raw_data
end
class Chunks < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root)
_read
end
def _read
@chunks = []
i = 0
while not @_io.eof?
@chunks << Chunk.new(@_io, self, @_root)
i += 1
end
self
end
attr_reader :chunks
end
##
# @see https://www.rfc-editor.org/rfc/rfc6386#section-9.1 Source
class Vp8 < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root)
_read
end
def _read
@frame_type = @_io.read_bits_int_le(1) != 0
raise Kaitai::Struct::ValidationNotEqualError.new(false, @frame_type, @_io, "/types/vp8/seq/0") if not @frame_type == false
@version = @_io.read_bits_int_le(3)
raise Kaitai::Struct::ValidationGreaterThanError.new(3, @version, @_io, "/types/vp8/seq/1") if not @version <= 3
@show_frame = @_io.read_bits_int_le(1) != 0
@len_first_partition = @_io.read_bits_int_le(19)
@_io.align_to_byte
@start_code = @_io.read_bytes(3)
raise Kaitai::Struct::ValidationNotEqualError.new([157, 1, 42].pack('C*'), @start_code, @_io, "/types/vp8/seq/4") if not @start_code == [157, 1, 42].pack('C*')
@width = @_io.read_bits_int_le(14)
@horizontal_scale = @_io.read_bits_int_le(2)
@height = @_io.read_bits_int_le(14)
@vertical_scale = @_io.read_bits_int_le(2)
@_io.align_to_byte
@data = @_io.read_bytes_full
self
end
attr_reader :frame_type
attr_reader :version
attr_reader :show_frame
attr_reader :len_first_partition
attr_reader :start_code
attr_reader :width
attr_reader :horizontal_scale
attr_reader :height
attr_reader :vertical_scale
attr_reader :data
end
##
# @see https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification Source
class Vp8l < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root)
_read
end
def _read
@signature = @_io.read_u1
raise Kaitai::Struct::ValidationNotEqualError.new(47, @signature, @_io, "/types/vp8l/seq/0") if not @signature == 47
@image_width_minus_1 = @_io.read_bits_int_le(14)
@image_height_minus_1 = @_io.read_bits_int_le(14)
@alpha_is_used = @_io.read_bits_int_le(1) != 0
@version_number = @_io.read_bits_int_le(3)
raise Kaitai::Struct::ValidationNotEqualError.new(0, @version_number, @_io, "/types/vp8l/seq/4") if not @version_number == 0
@_io.align_to_byte
@data = @_io.read_bytes_full
self
end
def image_height
return @image_height unless @image_height.nil?
@image_height = image_height_minus_1 + 1
@image_height
end
def image_width
return @image_width unless @image_width.nil?
@image_width = image_width_minus_1 + 1
@image_width
end
attr_reader :signature
attr_reader :image_width_minus_1
attr_reader :image_height_minus_1
##
# A hint only - it should not impact decoding. It should be `false` when
# all alpha values are 255 in the picture, and `true` otherwise.
attr_reader :alpha_is_used
attr_reader :version_number
attr_reader :data
end
class Vp8x < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root)
_read
end
def _read
@reserved1 = @_io.read_bits_int_be(2)
raise Kaitai::Struct::ValidationNotEqualError.new(0, @reserved1, @_io, "/types/vp8x/seq/0") if not @reserved1 == 0
@icc_profile = @_io.read_bits_int_be(1) != 0
@alpha = @_io.read_bits_int_be(1) != 0
@exif = @_io.read_bits_int_be(1) != 0
@xmp = @_io.read_bits_int_be(1) != 0
@animation = @_io.read_bits_int_be(1) != 0
@reserved2 = @_io.read_bits_int_be(1) != 0
raise Kaitai::Struct::ValidationNotEqualError.new(false, @reserved2, @_io, "/types/vp8x/seq/6") if not @reserved2 == false
@reserved3 = @_io.read_bits_int_be(24)
raise Kaitai::Struct::ValidationNotEqualError.new(0, @reserved3, @_io, "/types/vp8x/seq/7") if not @reserved3 == 0
@canvas_width_minus_1 = @_io.read_bits_int_le(24)
@canvas_height_minus_1 = @_io.read_bits_int_le(24)
raise Kaitai::Struct::ValidationGreaterThanError.new(4294967295 / canvas_width - 1, @canvas_height_minus_1, @_io, "/types/vp8x/seq/9") if not @canvas_height_minus_1 <= 4294967295 / canvas_width - 1
self
end
def canvas_height
return @canvas_height unless @canvas_height.nil?
@canvas_height = canvas_height_minus_1 + 1
@canvas_height
end
def canvas_width
return @canvas_width unless @canvas_width.nil?
@canvas_width = canvas_width_minus_1 + 1
@canvas_width
end
attr_reader :reserved1
attr_reader :icc_profile
attr_reader :alpha
attr_reader :exif
attr_reader :xmp
attr_reader :animation
attr_reader :reserved2
attr_reader :reserved3
attr_reader :canvas_width_minus_1
attr_reader :canvas_height_minus_1
end
class Xmp < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = nil)
super(_io, _parent, _root)
_read
end
def _read
@data = (@_io.read_bytes_full).force_encoding("UTF-8")
self
end
attr_reader :data
end
attr_reader :magic
attr_reader :len_data
attr_reader :webp
attr_reader :payload
attr_reader :_raw_payload
end