/******************************************************************************
 * SILENCE.CMD                                                                *
 *                                                                            *
 * This REXX script creates a brief (5 second, 48 KHz) WAV file consisting of *
 * nothing but silence, suitable for subsequently multiplexing into a DVD     *
 * menu as its audio track.  For example:                                     *
 *                                                                            *
 *   Create SILENCE.WAV:                                                      *
 *     silence.cmd                                                            *
 *                                                                            *
 *   Convert to DVD AC3 format (creates MENU_AUDIO.AC3):                      *
 *     ffmpeg -i silence.wav -ab 224 -ar 48000 menu_audio.ac3                 *
 *                                                                            *
 *   Multiplex into menu video file MENU_BG.M2V (creates MENU_BG.MPG):        *
 *     mplex -f 8 -o menu_bg.mpg menu_bg.m2v menu_audio.ac3                   *
 *                                                                            *
 * Generously provided by Don Hills; minor modifications by Alex Taylor.      *
 ******************************************************************************/
file_name = 'SILENCE.WAV'
file_time = 5        /*** seconds ***/

wav_type    = 1      /*** PCM ***/
mono_stereo = 2      /*** Stereo ***/
sample_rate = 48000  /*** 48 KHz ***/
sample_bits = 16     /*** bits per sample ***/

byte_rate = mono_stereo * sample_rate * (sample_bits % 8)
data_size = file_time * byte_rate
file_size = data_size + 36

call charout file_name, 'RIFF'
call charout file_name, reverse(right(d2c(file_size),4,'00'x))
call charout file_name, 'WAVE'
call charout file_name, 'fmt '
call charout file_name, reverse(right(d2c(16),4,'00'x))
call charout file_name, reverse(right(d2c(wav_type),2,'00'x))
call charout file_name, reverse(right(d2c(mono_stereo),2,'00'x))
call charout file_name, reverse(right(d2c(sample_rate),4,'00'x))
call charout file_name, reverse(right(d2c(byte_rate),4,'00'x))
call charout file_name, '0000'x /*** block alignment padding ***/
call charout file_name, reverse(right(d2c(sample_bits),2,'00'x))
call charout file_name, 'data'
call charout file_name, reverse(right(d2c(data_size),4,'00'x))
call charout file_name, left('',data_size,'00'x)
exit;