FILE STRUCTURE AUDIO MPEG FILE
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file

	a file has one or more 'frames'.

	a frame has a 'frame header' and 'frame data'
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frame length

	the frame length depends on the format and can vary per frame.
	the frame ends before the next sync header (see frame header).
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frame header

	the frame header of an audio mpeg file consist of 4 bytes, which
	are at the beginning of a frame. They don't have to be the same
	for every frame. (p.e. the bit 'padding' can change per frame)

	byte       0        1        2        3
	binary 11111111 1111abbc ddddeefg hhjjkmpp

		1 - sync header
		a - version
		b - layer
		c - error protection
		d - bit rate index
		e - sample rate index
		f - padding
		g - extension
		h - channel mode
		j - mode extension
		k - copyright 
		m - original
		p - emphasis
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1 - sync header

	must be 11111111 1111xxxx ($fffx)
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a - version

	0 = mpg-ii
	1 = mpg-i
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b - layer

	0 = layer-1
	3 = layer-2
	2 = layer-3
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c - error protection

	0 = on
	1 = off
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d - bit rate

	                     mpg-i
	(hex)   bps@38kHz  bps@44.1kHz  bps@48kHz
	$0          0            0           0
	$1         32           32          32
	$2         64           48          40
	$3         96           56          48
	$4        128           64          56
	$5        160           80          64
	$6        192           96          80
	$7        224          112          96
	$8        256          128         112
	$9        288          160         128
	$a        320          192         160
	$b        352          224         192
	$c        384          256         224
	$d        416          320         256
	$e        448          384         320
	
	                    mpg-ii
	(hex)   bps@16kHz  bps@22kHz  bps@24kHz
	$0          0            0           0
	$1         32            8           8
	$2         48           16          16
	$3         56           24          24
	$4         64           32          32
	$5         80           40          40
	$6         96           48          48
	$7        112           56          56
	$8        128           64          64
	$9        144           80          80
	$a        160           96          96
	$b        176          112         112
	$c        192          128         128
	$d        224          144         144
	$e        256          160         160
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e - sample rate

	      mpg-i     mpg-ii  (version)
	0 = 44.1 kHz    22 kHz
	1 =   48 kHz    24 kHz
	2 =   38 kHz    16 kHz
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f - padding

	1 = unused bits are filled (padding required)
	0 = all bits in frame are used
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g - extension 

	0 = none
	1 = private
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h - channel mode

	0 = stereo
	1 = joint stereo
	2 = dual channel
	3 = mono
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j = mode extension

	when encoding with joint stereo, this specifies to which freq.band
	it is bound.

            layer-1&2  layer-3
	0 =     4         0
	1 =     8         4
        2 =    12         8
        3 =    16        16
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k - copyright

	0 = no
	1 = yes
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m - original

	0 = no
	1 = yes
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p - emphasis

	0 = none
	1 = 50/15 microseconds
	3 = CITT j.17
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