Class: FilesHunter::Decoders::MP3

Inherits:
BeginPatternDecoder show all
Defined in:
lib/fileshunter/Decoders/MP3.rb

Overview

MP3 files can contain JPEG files

Constant Summary collapse

BEGIN_PATTERN_ID3V1 = 
'TAG'.force_encoding(Encoding::ASCII_8BIT)
BEGIN_PATTERN_ID3V1E = 
'TAG+'.force_encoding(Encoding::ASCII_8BIT)
BEGIN_PATTERN_ID3V2 = 
'ID3'.force_encoding(Encoding::ASCII_8BIT)
BEGIN_PATTERN_APEV2 = 
'APETAGEX'.force_encoding(Encoding::ASCII_8BIT)
BEGIN_PATTERN_MP3 = 
Regexp.new("(\xFF[\xE2-\xFF][\x00-\xEF]|#{BEGIN_PATTERN_ID3V2}|#{BEGIN_PATTERN_APEV2})", nil, 'n')
BITRATE_INDEX = 
[
  [ 32,  32,  32,  32,  8 ],
  [ 64,  48,  40,  48,  16 ],
  [ 96,  56,  48,  56,  24 ],
  [ 128, 64,  56,  64,  32 ],
  [ 160, 80,  64,  80,  40 ],
  [ 192, 96,  80,  96,  48 ],
  [ 224, 112, 96,  112, 56 ],
  [ 256, 128, 112, 128, 64 ],
  [ 288, 160, 128, 144, 80 ],
  [ 320, 192, 160, 160, 96 ],
  [ 352, 224, 192, 176, 112 ],
  [ 384, 256, 224, 192, 128 ],
  [ 416, 320, 256, 224, 144 ],
  [ 448, 384, 320, 256, 160 ]
]
SAMPLE_RATE_INDEX = 
[
  [ 44100, 22050, 11025 ],
  [ 48000, 24000, 12000 ],
  [ 32000, 16000, 8000 ]
]
MIN_ACCEPTABLE_TIME_MS = 
1000
MAX_ID3V2_FRAME_SIZE = 
256
APE_ITEM_KEY_TERMINATOR = 
"\x00".force_encoding(Encoding::ASCII_8BIT)
ID3V2_PADDING_CHAR = 
"\x00".force_encoding(Encoding::ASCII_8BIT)
TRAILING_00_REGEXP = 
Regexp.new("\x00*$".force_encoding(Encoding::ASCII_8BIT), nil, 'n')

Instance Method Summary collapse

Methods inherited from BeginPatternDecoder

#find_segments

Methods inherited from FilesHunter::Decoder

#segments_found, #setup

Instance Method Details

#check_begin_pattern(begin_pattern_offset, pattern_index) ⇒ Object 



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# File 'lib/fileshunter/Decoders/MP3.rb', line 51

def check_begin_pattern(begin_pattern_offset, pattern_index)
  if (@data[begin_pattern_offset] == "\xFF")
    header_bytes = @data[begin_pattern_offset+1..begin_pattern_offset+3].bytes.to_a
    return (((header_bytes[0] & 24) != 16) and
            ((header_bytes[0] & 6) != 0) and
            ((header_bytes[1] & 12) != 12) and
            ((header_bytes[2] & 3) != 2))
  else
    return true
  end
end

#decode(offset) ⇒ Object 



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# File 'lib/fileshunter/Decoders/MP3.rb', line 63

def decode(offset)
  ending_offset = nil

  cursor = offset
  nbr_ms = 0
  valid = false
  while (ending_offset == nil)
    #log_debug "=== @#{cursor} - Reading what's here"
    c_0_2 = @data[cursor..cursor+2]
    if (c_0_2 == BEGIN_PATTERN_ID3V1)
      if (@data[cursor..cursor+3] == BEGIN_PATTERN_ID3V1E)
        log_debug "=== @#{cursor} - Found ID3v1 extended tag"
        metadata( :id3v1e_metadata => {
          :title => read_ascii(cursor+4, cursor+63),
          :artist => read_ascii(cursor+64, cursor+123),
          :album => read_ascii(cursor+124, cursor+183),
          :speed => @data[cursor+184].ord,
          :genre => read_ascii(cursor+185, cursor+214),
          :start_time => read_ascii(cursor+215, cursor+220),
          :end_time => read_ascii(cursor+221, cursor+226)
        } )
        cursor += 227
      else
        # Just met an ID3v1 tag: skip 128 bytes
        log_debug "=== @#{cursor} - Found ID3v1 tag"
        metadata( :id3v1_metadata => {
          :title => read_ascii(cursor+3, cursor+32),
          :artist => read_ascii(cursor+33, cursor+62),
          :album => read_ascii(cursor+63, cursor+92),
          :year => read_ascii(cursor+93, cursor+96),
          :comments => read_ascii(cursor+97, cursor+126),
          :genre => @data[cursor+127].ord
        } )
        cursor += 128
        # Current MP3 is finished: id3v1 is forcefully at the end
        ending_offset = cursor
      end
    elsif (c_0_2 == BEGIN_PATTERN_ID3V2)
      # Just met an ID3v2 tag
      log_debug "=== @#{cursor} - Found ID3v2 tag"
      invalid_data("@#{cursor} - Invalid ID3v2 header") if ((@data[cursor+3].ord == 255) or (@data[cursor+4].ord == 255))
      # Compute the tag's size
      size = 10 # Header
      @data[cursor+6..cursor+9].bytes.each_with_index do |byte, idx|
        invalid_data("@#{cursor} - Invalid ID3v2 header in size specification (#{idx})") if (byte >= 128)
        size += (byte << ((8*(3-idx))-3+idx))
      end
      # Is there a footer?
      size += 10 if ((@data[cursor+5].ord & 16) == 16)
      cursor_end = cursor + size
      cursor += 10
      # Check if following is an extended header
      padding_size = 0
      extended_header_size = BinData::Uint32be.read(@data[cursor..cursor+3])
      if ((extended_header_size == 6) or
          (extended_header_size == 10))
        # There is an extended header
        extended_header_flags = BinData::Uint16be.read(@data[cursor+4..cursor+5])
        invalid_data("@#{cursor} - Invalid extended header flags.") if ((extended_header_flags & 0b01111111_11111111) != 0)
        has_crc = ((extended_header_flags & 0b10000000_00000000) != 0)
        invalid_data("@#{cursor} - Extended header declared size and CRC flag do not match.") if (((extended_header_size == 10) and (!has_crc)) or ((extended_header_size == 6) and (has_crc)))
        padding_size = BinData::Uint32be.read(@data[cursor+6..cursor+9])
        cursor += 10
        cursor += 4 if has_crc
      end
      # Read all frames
      id3v2_metadata = {}
      while ((cursor < cursor_end) and
             (@data[cursor] != ID3V2_PADDING_CHAR))
        # We are on a frame
        frame_id = @data[cursor..cursor+3]
        frame_size = BinData::Uint32be.read(@data[cursor+4..cursor+7])
        frame_flags = BinData::Uint16be.read(@data[cursor+8..cursor+9])
        invalid_data("@#{cursor} - Invalid ID3v2 frame flags: #{frame_flags}.") if ((frame_flags & 0b00011111_00011111) != 0)
        cursor += 10
        id3v2_metadata[frame_id] = read_ascii(cursor, cursor+((frame_size > MAX_ID3V2_FRAME_SIZE) ? MAX_ID3V2_FRAME_SIZE : frame_size)-1)
        cursor += frame_size
      end
      metadata( :id3v2_metadata => id3v2_metadata )
      # Get directly to the previously computed cursor to skip padding
      log_debug("@#{cursor} - Padding size (#{padding_size}) is different from what is being read (#{cursor_end-cursor}).") if (padding_size != cursor_end-cursor)
      cursor = cursor_end
    elsif (@data[cursor..cursor+7] == BEGIN_PATTERN_APEV2)
      log_debug "=== @#{cursor} - Found APEv2 tag"
      info = decode_ape_tag_header(cursor)
      invalid_data("@#{cursor} - APE tag header indicates no header whereas we have one.") if (!info[:has_header])
      invalid_data("@#{cursor} - APE tag header indicates it is a footer whereas we are on the header.") if (info[:on_footer])
      cursor += 32
      cursor_end_tag = cursor + info[:tag_size]
      ape_metadata = {}
      info[:nbr_items].times do |idx_item|
        item_key, item_value, cursor = decode_ape_tag_item(cursor)
        ape_metadata[item_key] = item_value
      end
      invalid_data("@#{cursor} - APE tag header is inconsistent. We should be at cursor #{cursor_end_tag-(info[:has_footer] ? 32 : 0)}") if (cursor != cursor_end_tag-(info[:has_footer] ? 32 : 0))
      metadata( :apev2_metadata => ape_metadata )
      if (info[:has_footer])
        # There is a footer
        invalid_data("@#{cursor} - Invalid APE tag footer magic.") if (@data[cursor..cursor+7] != BEGIN_PATTERN_APEV2)
        footer_info = decode_ape_tag_header(cursor)
        invalid_data("@#{cursor} - APEv2 tag footer indicates no footer whereas we have one.") if (!footer_info[:has_footer])
        invalid_data("@#{cursor} - APEv2 tag footer indicates it is a header whereas we are on the footer.") if (!footer_info[:on_footer])
        cursor += 32
      end
    else
      # We might be on a APEv1 tag, or real MP3 data, or at the end of our file.
      # APEv1 tag occurs only after the last MP3 frame, and before any ID3v1 tag.
      # APEv1 tag has no header, but a footer.
      ape_tag_decoded = false
      if (nbr_ms != 0)
        # Might be good to check for APEv1 tag
        cursor_begin = cursor
        begin
          ape_metadata = {}
          nbr_items = 0
          while (@data[cursor..cursor+7] != BEGIN_PATTERN_APEV2)
            item_key, item_value, cursor = decode_ape_tag_item(cursor)
            ape_metadata[item_key] = item_value
            nbr_items += 1
            log_debug "=== @#{cursor} - Decoded APEv1 tag item: #{item_key.inspect} => #{item_value[0..31].inspect}"
          end
          # Here we are on an APE Tag footer
          footer_info = decode_ape_tag_header(cursor)
          invalid_data("@#{cursor} - APEv1 tag footer indicates no footer whereas we have one.") if (!footer_info[:has_footer])
          invalid_data("@#{cursor} - APEv1 tag footer indicates it is a header whereas we are on the footer.") if (!footer_info[:on_footer])
          invalid_data("@#{cursor} - APEv1 tag footer indicates #{footer_info[:nbr_items]} tag items, whereas we read #{nbr_items}") if (footer_info[:nbr_items] != nbr_items)
          log_debug "=== @#{cursor} - Found APEv1 tag"
          cursor += 32
          ape_tag_decoded = true
          metadata( :apev1_metadata => ape_metadata )
        rescue InvalidDataError, TruncatedDataError, AccessAfterDataError
          # Maybe it is not an APEv1 tag.
          # Scratch it and consider a normal MP3 frame.
          #log_debug("=== @#{cursor_begin} - Failed to decode as APEv1 tag: #{$!}")
          cursor = cursor_begin
          ape_tag_decoded = false
        end
      end
      if (!ape_tag_decoded)
        # Real MP3 data or end of file
        info = nil
        begin
          info = decode_mp3_frame_header(cursor)
        rescue InvalidDataError
          if (nbr_ms >= MIN_ACCEPTABLE_TIME_MS)
            # Consider the file was finished
            #log_debug "=== @#{cursor} - Garbage data found. Should be end of file."
            ending_offset = cursor
          else
            # Problem
            raise
          end
        end
        if (ending_offset == nil)
          #log_debug "=== @#{cursor} - Found MP3 data"
          # Go see after
          cursor += info[:size]
          # Consider we have valid data only if we have enough milliseconds
          nbr_ms += info[:nbr_ms]
          if ((!valid) and (nbr_ms >= MIN_ACCEPTABLE_TIME_MS))
            valid = true
            found_relevant_data(:mp3)
          end
          metadata( :nbr_ms => nbr_ms )
        end
      end
    end
    if ((nbr_ms >= MIN_ACCEPTABLE_TIME_MS) and
        (cursor == @end_offset))
      ending_offset = cursor
    end
    progress(cursor)
  end

  return ending_offset
end

#get_begin_pattern ⇒ Object 



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# File 'lib/fileshunter/Decoders/MP3.rb', line 47

def get_begin_pattern
  return BEGIN_PATTERN_MP3, { :max_regexp_size => 8 }
end