This wrapper script will fork castnow. It accepts all castnow options and forks the process to the background.

castnow-fork.sh

#!/bin/bash
# 2016.10.08 - jamespfinn@gmail.com
# https://github.com/jamespfinn
#
# This script will fork an instance of castnow (https://github.com/xat/castnow).  
# All options passed to this script will be passed to castnow
# e.g.: 
#   $ ./castnow-fork.sh file1.mp3 file2.mp3 --address 192.168.1.44
#
# This script has only been tested on Linux
# To make it work on OSX the output from 'ps' needs to be handled differently.  
# See https://github.com/xat/castnow/issues/169#issuecomment-259262796 for the 
# necessary modifications. 
#
OUT1=/tmp/castnow-fork.out
OUT2=/dev/null
set -m
{
  { castnow $@ &>$OUT1 ; } & 
  export pid=$!
  ( 
    while kill -0 $pid ; do 
      if [ "$(ps -o stat -p $pid | tail -1 | cut -c1)" == "S" ]; then 
        { 
          echo killing $pid...
          kill $pid
        }
      fi
    done
  )
} &> $OUT2