afGetFrameSize returns the frame size in bytes for a specified audio
track.

SYNOPSIS
#include <audiofile.h>

float afGetFrameSize (AFfilehandle file, int track, int expand3to4);

PARAMETERS
file is a valid AFfilehandle.

track is an integer which refers to a specific audio track in the
file.  At present no supported audio file format allows for more than
one audio track within a file, so track should always be
AF_DEFAULT_TRACK.

expand3to4 is a boolean-valued integer indicating whether frame size
calculation will treat 24-bit data as having a size of 3 bytes or 4
bytes.

DESCRIPTION
afGetFrameSize returns the number of bytes in a frame in the given
track of the specified file.

A sample frame consists of one or more samples.  For a monaural track,
a sample frame will always contain one sample.  For a stereophonic
track, a sample frame will always contain two samples, one for the left
channel and one for the right channel.

A non-zero value of expand3to4 should be used when calculating the
frame size for storage in memory (since 24-bit audio data is presented
in memory as a 4-byte sign-extended integer), while a value of zero
should be used for calculating storage on disk where no padding is
added.  The parameter expand3to4 is ignored unless the specified audio
track contains 24-bit audio data.
