Real Lossless Codec

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Revision as of 15:35, 10 March 2012 Kostya (Talk | contribs) ← Previous diff		Revision as of 16:17, 10 March 2012 Kostya (Talk | contribs) (→Frame format) Next diff →
Line 25:		Line 25:
	Data is read MSB.		Data is read MSB.
		+
		+	block header
		+	channel data 1
		+	if (stereo)
		+	channel data 2
		+
		+	Each channel is then restored by applying filter and in stereo case channels are recombined.
	=== Block header ===		=== Block header ===
Line 59:		Line 66:
	| align="center" | 4 || align="center" | 2 || align="center" | 17 || align="center" | 2 || align="center" | 17 || align="center" | (L+R)/2, (L-R)/2		| align="center" | 4 || align="center" | 2 || align="center" | 17 || align="center" | 2 || align="center" | 17 || align="center" | (L+R)/2, (L-R)/2
	|}		|}
		+
		+	=== Block data ===
		+
		+	code from tree 0 (0..642) - something to do with filter length
		+	also if code == 642 just read raw data and return it

---

Revision as of 16:17, 10 March 2012

• FOURCCs: ralf
• Company: RealNetworks
• Samples: http://samples.mplayerhq.hu/A-codecs/lossless/ (luckynight.rmvb)

This is RealNetworks lossless audio codec.

Audio header in rm files is different from other Real audio codecs; the interface of the binary decoder is also different.

Contents 1 Extradata format 2 Frame format 2.1 Block header 2.2 Block data

Extradata format

Numbers are stored big-endian.

bytes  0- 3 - codec FOURCC, always "LSD:"
bytes  4- 5 - version
bytes  8- 9 - number of channels
bytes 10-11 - bits per sample
bytes 12-15 - sampling rate
bytes 16-19 - block size in samples?
bytes 20-23 - ignored?

Known decoder support only 1/2 channel 16-bit audio with sampling rate up to 96 kHz.

Frame format

Data is read MSB.

 block header
 channel data 1
 if (stereo)
   channel data 2

 Each channel is then restored by applying filter and in stereo case channels are recombined.

Block header

 get frame length code
 if (stereo)
   decoding_mode = get_bits(2) + 1;
 else
   decoding_mode = 0;

Frame length code:

   64 - 11110
  128 - 11111
  256 - 1110
  512 - 110
 1024 - 10
 2048 - 0

Decoding mode specifies table sets, bits and channel recombining:

Mode	tableset1	bits1	tableset2	bits2	Channel decoupling
0	0	16	n/a	n/a	mono
1	0	16	0	16	L, R
2	0	16	2	17	L+R, R
3	1	16	2	17	L, R-L
4	2	17	2	17	(L+R)/2, (L-R)/2

Block data

 code from tree 0 (0..642) - something to do with filter length
 also if code == 642 just read raw data and return it