EE-320-v01| Application Note
Engineer-to-Engineer Note
EE-320
a
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Implementing an Ogg Vorbis Decoder on SHARC Processors
Contributed by Jeyanthi Jegadeesan and Kulin Seth Rev 1 June 10, 2008
This EE-Note discusses the real-time implementation of an Ogg-Vorbis decoder on SHARC processors. The Ogg Vorbis decoder is implemented on the ADSP-21364 and ADSP-21369 SHARC processors, although the same concepts apply for all ADSP-2136x SHARC processors. The ADSP-21364 and ADSP21369 EZ-KIT Lite boards are used as the hardware platform, and the VisualDSP++ development tools are used for the software development of the application. The VisualDSP++ source code for the decoder application is provided with this EE-Note in the associated .ZIP file. Throughout this document, details about the following items will be broadly addressed: Ogg Vorbis codecs Visual C++ as a cross-reference tool Architectural advantages of ADSP-2136x SHARC processors Decoder workflow Implementation on ADSP-2136x SHARC processors Features of VisualDSP++ tools Optimization MIPS calculation
Ogg Vorbis Codecs
Ogg is the Xiph.org foundation's container format that holds multimedia data. Vorbis is a fully open, patent-free, royalty-free audio compression format, which uses Ogg format to store its bit streams as files. In many respects, Vorbis is similar in function to the MPEG-1/2 layer 3 (MP3) format and the newer MPEG-4 (AAC) format. This codec was designed for mid-to-high quality (8-kHz to 48-kHz bandwidth, >16-bit, polyphonic) audio at variable bit rates from 16 to 128 Kbps/channel, so it is an ideal format for music. The Ogg transport bit stream is designed to provide framing, error protection and seeking structure for higher-level codec streams that consist of raw, unencapsulated data packets, such as the Vorbis audio codec or Tarkin video codec. Vorbis encodes short-time blocks of PCM data into raw packets of bitpacked data. These raw packets may be used directly by transport mechanisms that provide their own framing and packet-separation mechanisms (such as UDP datagrams). For stream-based storage (such as
files) and transport (such as TCP streams or pipes), Vorbis uses the Ogg bit stream format to provide framing/sync, sync recapture after error, landmarks during seeking, and enough information to properly
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