sunau¶

Stuff to parse Sun and NeXT audio files.

An audio file consists of a header followed by the data. The structure of the header is as follows.

magic word

header size

data size

encoding

sample rate

# of channels

info

The magic word consists of the 4 characters ‘.snd’. Apart from the info field, all header fields are 4 bytes in size. They are all 32-bit unsigned integers encoded in big-endian byte order.

The header size really gives the start of the data. The data size is the physical size of the data. From the other parameters the number of frames can be calculated. The encoding gives the way in which audio samples are encoded. Possible values are listed below. The info field currently consists of an ASCII string giving a human-readable description of the audio file. The info field is padded with NUL bytes to the header size.

Usage.

Reading audio files:

f = sunau.open(file, ‘r’)

where file is either the name of a file or an open file pointer. The open file pointer must have methods read(), seek(), and close(). When the setpos() and rewind() methods are not used, the seek() method is not necessary.

This returns an instance of a class with the following public methods:

getnchannels() – returns number of audio channels (1 for

mono, 2 for stereo)

getsampwidth() – returns sample width in bytes getframerate() – returns sampling frequency getnframes() – returns number of audio frames getcomptype() – returns compression type (‘NONE’ or ‘ULAW’) getcompname() – returns human-readable version of

compression type (‘not compressed’ matches ‘NONE’)

getparams() – returns a tuple consisting of all of the

above in the above order

getmarkers() – returns None (for compatibility with the

aifc module)

getmark(id) – raises an error since the mark does not

exist (for compatibility with the aifc module)

readframes(n) – returns at most n frames of audio rewind() – rewind to the beginning of the audio stream setpos(pos) – seek to the specified position tell() – return the current position close() – close the instance (make it unusable)

The position returned by tell() and the position given to setpos() are compatible and have nothing to do with the actual position in the file. The close() method is called automatically when the class instance is destroyed.

Writing audio files:

f = sunau.open(file, ‘w’)

where file is either the name of a file or an open file pointer. The open file pointer must have methods write(), tell(), seek(), and close().

This returns an instance of a class with the following public methods:

setnchannels(n) – set the number of channels setsampwidth(n) – set the sample width setframerate(n) – set the frame rate setnframes(n) – set the number of frames setcomptype(type, name)

– set the compression type and the

human-readable compression type

setparams(tuple)– set all parameters at once tell() – return current position in output file writeframesraw(data)

– write audio frames without pathing up the

file header

writeframes(data)

– write audio frames and patch up the file header

close() – patch up the file header and close the

output file

You should set the parameters before the first writeframesraw or writeframes. The total number of frames does not need to be set, but when it is set to the correct value, the header does not have to be patched up. It is best to first set all parameters, perhaps possibly the compression type, and then write audio frames using writeframesraw. When all frames have been written, either call writeframes(‘’) or close() to patch up the sizes in the header. The close() method is called automatically when the class instance is destroyed.