OggCELT

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CELT is an experimental audio codec for use in low-delay communication.
CELT is an experimental audio codec for use in low-delay communication.
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The [http://www.celt-codec.org/ CELT homepage] has all the project info.
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The name stands for "Code-Excited Lapped Transform". It applies some of the [[Wikipedia:CELP|CELP]] principles, but does everything in the frequency domain, which removes some of the limitations of CELP.
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The CELT codec is meant to close the gap between [[Vorbis]] and [[Speex]] for applications where both high quality audio and low delay are desired.  It is a
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Current features include:
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* '''Ultra-low latency (typically from 3 to 9 ms)'''
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* Full audio bandwidth (44.1 kHz and 48 kHz)
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* Stereo support
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* Packet loss concealment
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* Constant bit-rates from 32 kbps to 128 kbps and above
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* A fixed-point version of the encoder and decoder
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The [http://www.celt-codec.org/ CELT homepage] has all additional info as well as samples.
== Ogg mapping (experimental) ==
== Ogg mapping (experimental) ==

Revision as of 22:26, 25 April 2008

CELT is an experimental audio codec for use in low-delay communication.

The name stands for "Code-Excited Lapped Transform". It applies some of the CELP principles, but does everything in the frequency domain, which removes some of the limitations of CELP.

The CELT codec is meant to close the gap between Vorbis and Speex for applications where both high quality audio and low delay are desired. It is a

Current features include:

  • Ultra-low latency (typically from 3 to 9 ms)
  • Full audio bandwidth (44.1 kHz and 48 kHz)
  • Stereo support
  • Packet loss concealment
  • Constant bit-rates from 32 kbps to 128 kbps and above
  • A fixed-point version of the encoder and decoder

The CELT homepage has all additional info as well as samples.

Ogg mapping (experimental)

The following is a draft. It is at best incomplete and at worst completely broken. In any case, it is not an "official" Xiph spec/codec, so use with care.


Default field type: LITTLE ENDIAN unsigned integer

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1| Byte
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | codec_id: Identifier char[8]: 'CELT    '                      | 0-3
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               | 4-7
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | codec_version: char[20]                                       | 8-11
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               | 12-15
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               | 16-19
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               | 20-23
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               | 24-27
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | version_id                                                    | 28-31
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | header_size                                                   | 32-35
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | mode                                                          | 36-39
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | sample_rate                                                   | 40-43
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | nb_channels                                                   | 44-47
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | bytes_per_packet                                              | 48-51
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | extra_headers                                                 | 52-55
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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