I haven't made much progress toward a portable sound file system, but I
want to revisit this problem. I'm still using my own library in Nyquist
and Aura, but I would like to use something with a wider base of users
and developers. I can put some resources into this, and I'm curious
about other people's opinions on the state of the art and what if
anything should be done.
Recently, a student and I re-examined libsndfile and libaudiofile, and I
was disappointed by both. Libsndfile uses a different scale factor on
input and output. This seems to stem from a view that audio data is
basically an analog approximation and a little distortion is OK. My view
is that the implementation should follow a precise specification and the
relationship between float and int samples should be fixed (e.g. ints
can be viewed as binary fractions, making the scale factor 2^N).
Libsndfile does not support Ogg Vorbis, mp3, or SDIF, although it does
support a lot of formats and at least one that would allow files longer
than 2^32 bytes. Libaudiofile reads data with a scale factor of 1/(2^N -
1) which seems wrong, but I think this can be changed through the API.
Worse, it rounds floats toward zero rather than rounding to the nearest
value, introducing a nonlinearity on output. In spite of the features
and support, I think both libsndfile and libaudiofile have some
fundamental (although easily fixed) problems.
My sense is that writing a new sound file library is a waste of effort
and would not serve many users. I could modify libsndfile, but Erik de
Castro Lopo (creator of libsndfile) would consider a fork of the project
to be "hostile". (Is that important? Audacity already keeps a private
copy of libsndfile, but probably more for source control than anything
else.) I could also work on libaudiofile, but adding a lot of new file
formats there seems like duplication of effort. There's also the
legality question for mp3 support -- I don't understand this, but it
seems to me that dynamically linking to Lame as does Audacity would be
relatively easy.
Meanwhile, the portmedia project is up at SourceForge. I'm slowly
getting things set up there. If anyone would like to
adapt/recreate/update the PortMusic web pages on SourceForge, let me know.
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