RealAudio sipr

• FOURCC: sipr
• Company: RealNetworks
• Samples: http://samples.mplayerhq.hu/real/AC-sipr/

Audio codec found in RealMedia files, not as common as cook.

Allegedly the same codec as ACELP.net. May be partly based on G.729, however RealAudio predates the finalization of the G.729 specifications for the 6.5 kbit/s and 11.8 kbit/s variants. ITU-T G.729 page

Codec library with debugging symbols: v50b3_linux20elf.tar.gz

Sipr flavors

0  6.5 Kbps Voice
1  8.5 Kbps Voice
2  5 Kbps Voice
3  16 Kbps Voice

Bit stream frame format

16 Kbps Voice

Bits	Meaning
1	Switched MA predictor
7	LSP quantization, index 1
8	LSP quantization, index 2
7	LSP quantization, index 3
7	LSP quantization, index 4
7	LSP quantization, index 5
First subframe
9	Pitch delay
4	Gain codebook index
9	Fixed codebook index (pulses 1 and 6)
9	Fixed codebook index (pulses 2 and 7)
9	Fixed codebook index (pulses 3 and 8)
9	Fixed codebook index (pulses 4 and 9)
9	Fixed codebook index (pulses 5 and 10)
Second subframe
9	Pitch delay
4	Gain codebook index
9	Fixed codebook index (pulses 1 and 6)
9	Fixed codebook index (pulses 2 and 7)
9	Fixed codebook index (pulses 3 and 8)
9	Fixed codebook index (pulses 4 and 9)
9	Fixed codebook index (pulses 5 and 10)

Decoding of the pitch (adaptive codebook) vector

Decode pitch lag

16 Kbps Voice, 1/3 resolution

<math>\left [29 \frac{1}{3}; 159\right] </math>