Audible Audio

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Proprietary container format from audible.com. There is no published specification. It may contain one of five different encodings which are numbered 1 thru 5. 1-3 are rumored to be ACELP.net at varying bitrates. #4 is MP3. #5 is some unknown Sony format.

Parsing metadata

This following Ruby code works for parsing the metadata on the only sample available:

 video = File.new(ARGV[0])
 video.read(189) # skip header
 (1..19).each { |x|
   sizes = video.read(8).unpack('NN')
   key = video.read(sizes[0].to_i)
   value = video.read(sizes[0].to_i+1)
   puts "#{x} key(#{sizes[0].to_i})=#{key} value(#{sizes[0].to_i)=#{value}"
 }

Sample output (stripped):

 13 key(5)=codec value(7)=acelp85
 16 key(10)=HeaderSeed value(10)=1158166611
 18 key(9)=HeaderKey value(43)=3759801365 1641076194 2988088058 4282540117
 19 key(15)=EncryptedBlocks value(5)=39333