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Speex Audio Codec, Version 1.2
Format Description Properties
- ID: fdd000259
- Short name: SPX_1_2
- Content categories:
- Format Category:
- Other facets:
unitary, binary, sampled
- Last significant update:
- Draft status: Full
Identification and description
||Speex Audio Codec, Version 1.2
||Speech codec designed for packet networks and voice over IP (VoIP) applications but not for mobile phones. File-based compression is also supported. The flexible codec is based on Code Excited Linear Prediction (CELP) and supports a wide range of speech quality and bit-rates. The VoIP-oriented design means that Speex is robust to lost but not to corrupted packets. Because Speex is targeted at a wide range of devices, its memory footprint is modest and its complexity, which is variable, may also be modest.
||Generally used for final-state, end-user delivery.
|Relationship to other formats
Ogg Speex Audio Format
||CELP, Code Excited Linear Prediction. Not documented at this Web site at this time.
|LC experience or existing holdings
||In 2007, consideration was being given to the use of Ogg_SPX for service copies of oral history recordings for access via the Web.
||LCPM preferred for master copies.
||Fully documented. Developed by xiph as an open source and patent-free project.
||The Speex Codec Manual, Version 1.2 Beta 2, May 22, 2007.
| Licensing and patents
||The specification provides the license in Appendix D. It is inspired by the BSD (Berkeley Software Distribution) family of free, near-public-domain software licenses. Paraphrasing appendix D: redistributions of source code or binary versions are free but must retain the copyright notice and other wording; the name of the Xiph.org Foundation or of contributors may not be used to endorse or promote products without specific prior written permission.
||Encoding depends upon algorithms and tools to read; requires sophistication to build tools.
|Technical protection considerations
Quality and functionality factors
|Fidelity (high audio resolution)
||This is compression designed for comprehensible speech, not for a rich representation of a full audio spectrum and dynamic range. Paraphrased from the specification: CELP was selected as the encoding technique; it scales well to both low bit-rates (e.g. DoD CELP @ 4.8 kbps) and high bit-rates (e.g. G.728 @ 16 kbps). Speex is designed for
three different sampling rates: 8 kHz, 16 kHz, and 32 kHz, referred to as narrowband (telephone quality), wideband, and ultra-wideband. The encoding process is controlled most of the time by a quality parameter that ranges from 0 to 10. In constant bit-rate (CBR) operation, the quality parameter is an integer, while for variable bit-rate (VBR), the parameter is a float. There is also Average Bit Rate that dynamically adjusts VBR quality in order to meet a specific target bit-rate. The management of bit-rate is important in VoIP, where the maximum must be low enough for the communication channel.
||Provides intensity stereo coding.1
|Support for user-defined sounds, samples, and patches
|Functionality beyond normal rendering
||Not investigated at this time.
File type signifiers
|Internet Media Type
|| For Speex-in-Ogg, from the main part of the specification. However, the recommended practice now seems to use the codecs parameter as described in RFC 5334.
|Internet Media Type
||From RFC 5334.
|Internet Media Type
||Proposed in various drafts of RTP Payload Format for the Speex Codec. e.g., http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-speex-05.txt (obsolete and hence not actively linked from this format description).
||Ogg Codec Identifier. An 8-character string, with 3 trailing spaces, used within Ogg container, at beginning of first header page to identify codec. See IETF RFC 5334
||Codec identier, long ID. From http://wiki.xiph.org/index.php/Oggless#Codec_Identifier:
- Xiph wiki (http://wiki.xiph.org/index.php/Main_Page).
- IETF RFC 5334 (http://www.rfc-editor.org/rfc/rfc5334.txt). Introduces the use of the codecs parameter to distinguish encodings within the Ogg container format.
- Oggless (http://wiki.xiph.org/index.php/Oggless). Documentation for xiph codecs in containers other than Ogg.
Friday, 20-Feb-2009 14:31:59 EST