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pyvorbis - a Python wrapper for the Ogg/Vorbis library
Ogg/Vorbis is available at http://www.xiph.org
This is the Vorbis module. You will need to download and install the
Python ogg module (available wherever you got this) before you can
build the vorbis module.
Access this module via "import ogg.vorbis" or "from ogg.vorbis import
*". You can now write Python programs to encode and decode Ogg Vorbis
files (encoding is quite a bit more involved). The module is
self-documenting, though I need to update quite a bit of it. Look at
test/ogg123.py, test/short.py, and test/enc.py for very simple
demonstrations of the module interface.
And if anyone is wondering why I have things separated into a main
module "ogg" and a submodule "ogg.vorbis", vorbis is the audio subset
of the ogg bitstream. In the future there will likely be a video part
of the ogg bistream, and nothing in the ogg modulue really has to know
about anything specific in the vorbis module.
To build, you need the distutils package, availible from
http://www.python.org/sigs/distutils-sig/download.html (it comes with
Python 2.0). Run config_unix.py first to generate a Setup file. Then
run "python setup.py build" to build and then as root run "python
setup.py install". You may need to run config_unix.py with a
"--prefix" option if you installed your ogg or vorbis libraries in a
weird place. You can also pass --with-ogg-dir and --with-vorbis-dir
arguments if they're installed separately. If you have problems with
the configure script, check the output of conifg.log for specific
errors.
To decode, you'll basically want to create a VorbisFile object and
read data from that. You can then write the data to a sound
device. I've used both the pyao wrapper (also by me) and the
linuxsounddev module present in Python2.0.
To encode, you need to feed a VorbisDSPState object PCM data as one
array of floating point values ranging from -1.0 ... 1.0 per
channel. You can do this in pure Python, but it almost doubles the
time it takes to encode. The other option is to read data using the
python "wave" module and write it to the VorbisDSPState directly using
the x.write_wav(mywave.readframes(n)) call. This will only work with
16-bit Wave files.
Perhaps you are wondering how much of a performance hit you'll be
taking using the Python bindings versus straight C. Well, I've tried
to make things as fast as possible, but of course nothing's
perfect. Decoding a file, top reports about the same CPU usage for my
ogg123.py and the C implementation of ogg123. For encoding, it's about
twice as slow as oggenc if you're using my test enc.py file (parsing
the wave file somewhat by hand). If you use the write_wav function,
it's only about 3% slower than oggenc.
Vorbis Comment
--------------
A frequent question is how to edit and then write comments. This was
not possible until recently. To implement this, I have taken the code
from the vorbiscomment program, which is by Michael Smith and released
under the LGPL. It has not been modified by me (Andrew).
There was an old way of dealing with VorbisComment objects, which
sucked, so I won't tell you how to use it. It still works but is
deprecated.
The current way of using VorbisComment objects is just to convert to
and from Python dictionaries. Note that there can be multiple entries
per key and that keys are case-insensitive 7-bit ASCII, because that's
how vorbis comments work. So I might do:
>>> import ogg.vorbis
>>> v = {'mykey' : ['myval1', 'myval2']}
>>> v['artist'] = u'andrew' # Unicode string for Python >= 1.6
>>> print v
{'artist': 'andrew', 'mykey': ['myval1', 'myval2']}
>>> comments = ogg.vorbis.VorbisComment(v)
There, we made a comment object from a dictionary. The values of the
dictionary are either strings or lists or strings. We can also convert
back to a dictionary, though it'll look a little different:
>>> print comments.as_dict()
{'ARTIST': [u'andrew'], 'MYKEY': ['myval1', 'myval2']}
We could also have gotten a comment object from a vorbis file:
>>> import ogg.vorbis
>>> f = ogg.vorbis.VorbisFile('test.ogg')
>>> print f.comment().as_dict()
To write the comments to an existing ogg/vorbis file, call v.write_to
or v.append_to. The former will add lots of keys, so if you already
have an artist key, and you add another, you now have two arist keys
in that file. Note that currently the VENDOR tag (which is special)
doesn't get written to the file. I'll have to look into that.
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