sample stdout spying script for a process using strace (in this case for mplayer)

mplayer stdout tracking

#track all (write sys call) output but clear from system call functions(only the text in quotes)
strace -p$(pgrep mplayer |head -n1 ) -s9999 -e write  2>&1 |grep -Po '".*?"'
#track volume changes
strace -p$(pgrep mplayer |head -n1 ) -s9999 -e write  2>&1 |grep -Po 'KVolume.*? %'
#track information and volume changes
strace -p$(pgrep mplayer |head -n1 ) -s9999 -e write  2>&1 |grep -Po 'KVolume.*? %|Title:.*?\\n|Album:.*?\\n|Year:.*?\\n|Track:.*?\\n'
#or 
strace -p$(pgrep mplayer |head -n1 ) -s9999 -e write  2>&1 |grep -Po 'KVolume.*?\\n|Title:.*?\\n|Album:.*?\\n|Year:.*?\\n|Track:.*?\\n'