LAME header
-----------

120 bytes	Xing header
9 bytes		lame version string (for example, "LAME3.12 (beta 6)")
1 byte		revision and vbr method:
  4 bits		revision
  4 bits		vbr method
1 byte		lowpass filter frequency
4 bytes		peak signal amplitude
2 bytes		radio replay gain
2 bytes		audiohpile replay gain
1 byte 		flags 1:
  4 bits		auth type
  1 bit			Naoki's psycho acoustic model was used
  1 bit			safe joint
  1 bit			no gap more
  1 bit			no gap previous
1 byte		abr bitrate (0xFF means invalid)
12 bits		encoding delay
12 bits		encoding padding
1 byte		flags 2:
  2 bits		noise shaping
  3 bits		stereo mode
  1 bit			non optimal
  2 bits		source frequency
1 byte		unused
2 bytes		preset value
4 bytes		music length
2 bytes		music crc
2 bytes		crc

Values of vbr method:
  0: ? (-vbr 5)
  1: ? (-vbr 0)
  2: ? (-vbr 3)
  3: ? (-vbr 2 and -vbr 6)
  4: ? (-vbr 4)
  5: ? (-vbr 1)
 >5: unused

Values of source frequency:
  0: < 32000 kHz
  1:   44100 kHz
  2:   48000 kHz
  3: > 48000 kHz

Values of stereo mode:
  0: mono
  1: stereo
  2: dual channel
  3: joint stereo
  4: joint stereo with forced mid-side stereo
  5: auto mid-side stereo
  6: unused/reserved
  7: default fallback (unknown)

Note: the Xing header tag may be the string "Info" in case of non-VBR stream.


References
----------

MPlayerXP sources:
http://mplayerxp.sf.net/

LAME 3.93.1 sources:
http://www.mp3dev.org/ or http://lame.sf.net/

PlusV specification:
http://www.plusv.org/

FAAD sources:
http://www.audiocoding.com/