Sustainability of Digital Formats
 Planning for Library of Congress Collections

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Identification and description

Full name	Ogg Speex Audio Format
Description	File format and bitstream encoding for for spoken content, targeted at a wide range of devices other than mobile phones.
Production phase	Generally used for final-state, end-user delivery.
Relationship to other formats
Subtype of	Ogg, Ogg File Format
Contains	SPX_1_2, Speex Audio Codec, Version 1.2

Local use

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.
LC preference	WAVE_LCPM or WAVE_LPCM_BWF preferred for master copies.

Sustainability factors

Disclosure	Developed by xiph as an open source and patent-free project.
Documentation	See Ogg and SPX_1_2.
Adoption	See Ogg.
Licensing and patents	See SPX_1_2.
Transparency	See SPX_1_2.
Self-documentation	See Ogg.
External dependencies	None.
Technical protection considerations	See Ogg.

Quality and functionality factors

Sound
Normal rendering	Good support.
Fidelity (high audio resolution)	See SPX_1_2.
Multiple channels	See SPX_1_2.
Support for user-defined sounds, samples, and patches	None.
Functionality beyond normal rendering	Not investigated at this time.

File type signifiers

Tag	Value	Note
Filename extension	spx	The specification states that Speex tools (speexenc, speexdec) do not rely on the extension; any extension will work.
Internet Media Type	audio/x-speex	For Speex-in-Ogg, from the main part of the specification.
Internet Media Type	audio/speex	From the February 2008 draft of RTP Payload Format for the Speex Codec; link expires in August 2008, thus not active from this page: http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-speex-05.txt.
Magic numbers	Hex: 4F 67 67 53 00 02 00 00 00 00 00 00 00 00 ASCII: OggS	See also Notes below.

Notes

General

Regarding file type signifiers, from the Speex specification: The first packet of the Ogg_SPX file contains the Speex header [presented in figure 6.1 on page 23]. All integer fields in the headers are stored as little-endian. The speex_string field must contain the [Speex with 3 trailing spaces], which identifies the bit-stream. The next field, speex_version contains the version of Speex that encoded the file. For now, refer to speex_header.[ch] for more info. The beginning of stream (b_o_s) flag is set to 1 for the header. The header packet has packetno=0 and granulepos=0. The second packet contains the Speex comment header. The format used is the Vorbis comment format described here: http://xiph.org/vorbis/doc/v-comment.html. This packet has packetno=1 and granulepos=0. The third and subsequent packets each contain one or more (number found in header) Speex frames. These are identified with packetno starting from 2 and the granulepos is the number of the last sample encoded in that packet. The last of these packets has the end of stream (e_o_s) flag is set to 1.

History

Format specifications

• Ogg Vorbis documentation menu (http://www.xiph.org/vorbis/doc/). Includes general information about Ogg files.
• The Speex Codec Manual, Version 1.2 Beta 2, May 22, 2007 (http://www.speex.org/docs/manual/speex-manual.pdf).

Useful references

URLs

• Ogg logical and physical bitstream overview (http://www.xiph.org/vorbis/doc/oggstream.html).
• Ogg logical bitstream framing (http://www.xiph.org/vorbis/doc/framing.html).