[opus] libopusfile

[Timothy B. Terriberry]

Traditionally, Vorbis provided a high-level API for decoding and seeking 
in Ogg Vorbis streams, called libvorbisfile, which was packaged 
alongside libvorbis. This was very useful for simple players and 
applications which just wanted to decode a file, without building an 
entire media framework.

The basic libopus is meant to be used in many contexts that do not 
require Ogg (such as RTP), and so it does not include any Ogg stream 
manipulation functions. I have just written a new library, libopusfile, 
that serves the same purpose as libvorbisfile, but for Ogg Opus files. 
Like libvorbisfile, it fully supports chaining and sample-accurate 
seeking. It also includes a few low-level Ogg-related functions 
corresponding to the ones traditionally found in libvorbis (header 
parsing and manipulation, etc.).

There are no current releases (or even autotools build support). There 
is, however, code in git:
http://git.xiph.org/?p=opusfile.git;a=summary

Also, API documentation:
https://mf4.xiph.org/jenkins/job/opusfile/ws/doc/html/index.html

Although this code was heavily based on libvorbisfile, it should still 
be treated as new code and is likely full of bugs. Please try it out and 
let me know what explodes.