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