Indeo Audio

• Format: 0x402
• Company: Intel, now Ligos
• Samples: http://samples.mplayerhq.hu/A-codecs/Indeo_audio/

Related to the Intel Music Coder but with different codebooks and bitstream format.

Header format

  bit  0   - should be zero
  bit  1   - should be zero
  bit  2   - stereo flag
  bits 3-8 - block size code
  bit  9   - codebook set selector (0 - no escapes, 1 - with escapes)
  bit 10   - codebook selector
  bit 11   - use raw coding
  
  bit 12   - SNR offset (-30 or -10)

Block size code:

  0, 34-50 - (block_size + 14) 16-bit words
  33       - 32 words
  1-32     - (block_size + 15) words
  51-63    - invalid value

Levels

There are 32 levels, coded with either one of codebooks or in raw form.

Decoding Huffman-coded levels is the same as in Intel Music Coder but with different tables.

Raw form:

  1st coefficient - 5 bits
  2nd coefficient - 7 bits
  others          - 4 bits per coefficient