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# frozen_string_literal: true
class GifReader
attr_reader :animated
EXTENSION_LABELS = [0xf9, 0x01, 0xff].freeze
GIF_HEADERS = %w(GIF87a GIF89a).freeze
class GifReaderException < StandardError; end
class UnknownImageType < GifReaderException; end
class CannotParseImage < GifReaderException; end
def self.animated?(path)
new(path).animated
rescue GifReaderException
false
end
def initialize(path, max_frames = 2)
@path = path
@nb_frames = 0
File.open(path, 'rb') do |s|
raise UnknownImageType unless GIF_HEADERS.include?(s.read(6))
# Skip to "packed byte"
s.seek(4, IO::SEEK_CUR)
# "Packed byte" gives us the size of the GIF color table
packed_byte, = s.read(1).unpack('C')
# Skip background color and aspect ratio
s.seek(2, IO::SEEK_CUR)
if packed_byte & 0x80 != 0
# GIF uses a global color table, skip it
s.seek(3 * (1 << ((packed_byte & 0x07) + 1)), IO::SEEK_CUR)
end
# Now read data
while @nb_frames < max_frames
separator = s.read(1)
case separator
when ',' # Image block
@nb_frames += 1
# Skip to "packed byte"
s.seek(8, IO::SEEK_CUR)
packed_byte, = s.read(1).unpack('C')
if packed_byte & 0x80 != 0
# Image uses a local color table, skip it
s.seek(3 * (1 << ((packed_byte & 0x07) + 1)), IO::SEEK_CUR)
end
# Skip lzw min code size
raise InvalidValue unless s.read(1).unpack('C')[0] >= 2
# Skip image data sub-blocks
skip_sub_blocks!(s)
when '!' # Extension block
skip_extension_block!(s)
when ';' # Trailer
break
else
raise CannotParseImage
end
end
end
@animated = @nb_frames > 1
end
private
def skip_extension_block!(file)
if EXTENSION_LABELS.include?(file.read(1).unpack('C')[0])
block_size, = file.read(1).unpack('C')
file.seek(block_size, IO::SEEK_CUR)
end
# Read until extension block end marker
skip_sub_blocks!(file)
end
# Skip sub-blocks up until block end marker
def skip_sub_blocks!(file)
loop do
size, = file.read(1).unpack('C')
break if size.zero?
file.seek(size, IO::SEEK_CUR)
end
end
end
module Paperclip
# This transcoder is only to be used for the MediaAttachment model
# to convert animated gifs to webm
class GifTranscoder < Paperclip::Processor
def make
return File.open(@file.path) unless needs_convert?
final_file = Paperclip::Transcoder.make(file, options, attachment)
attachment.instance.file_file_name = File.basename(attachment.instance.file_file_name, '.*') + '.mp4'
attachment.instance.file_content_type = 'video/mp4'
attachment.instance.type = MediaAttachment.types[:gifv]
final_file
end
private
def needs_convert?
options[:style] == :original && GifReader.animated?(file.path)
end
end
end
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