This field is deprecated. Specifies the number of samples per frame. For G.711
encoding mode, value must be a multiple of 8 samples.
For G.723 encoding mode, value must be a multiple of
240 samples. For G.729A, value must be a multiple of
80 samples. Note that 8 samples represent one millisecond
of voice data.
A value of 0 specifies a frame size equal to the minimum
for the encoding method (e.g 8 samples for G.711)