.TH vadpcm_enc 1P local "Silicon Graphics, Inc."
.SH NAME
vadpcm_enc \- ADPCM encoder for Ultra 64 audio
.SH SYNOPSIS
\f3vadpcm_enc\f1 -c codebook [-t] [-l minLoopLength] aifcFile codedFile
.SH DESCRIPTION
.I vadpcm_enc
encodes AIFC or AIFF sound files and produces a compressed binary file which 
which is used by the Ultra 64 audio library. The encoding algorithm is
based on a switched ADPCM algorithm which uses a 
.I codebook
to define a table of prediction coefficients. Coefficients from the table
are selected adaptively during encoding to give the best sound quality.
The Ultra 64 compressed sound format currently supports a single loop
point which should be defined in the input file's Instrument Chunk.
The codebook and loop point definitions are embedded in the final
output file.
.PP
Command line options are:
.RS 5
.TP 12
.B \-c <filename>
Defines a file which contains the prediction coefficient codebook
constructed by
.IR tabledesign(1).
.TP
.B -t 
Truncate the encoded file after the loop end point. The portion of the
sound after the loop end point is never used in audio playback. 
.TP
.B -l <value>
Set the minimum loop length in the encoded file (see Note below).
.SH NOTE
There is a restriction in the audio library which means that in a single
call to 
.I alAudioFrame(1P) 
a sound must only pass through two loop crossings.
To ensure less than two loop crossings the ADPCM encoder can `stretch' loops by
repeating them. The currently defined default minimum loop length
is 1600 samples. This default length can be changed (see above).
Loops shorter than the minimum loop length will be repeated until the
total loop length is larger than the minimum length. In a given application the required minimum loop length depends on the number of samples requested in a single call to 
.I alAudioFrame(1P)
and the maximum pitch shift incurred by the samples. For further information
see Chapter 14 of the developers manual.
.SH "SEE ALSO"
.IR tabledesign (1P),
.IR vadpcm_dec (1P)