[FFmpeg-user] file for preset 'iphone' not found

[aris sirajawali]

 I try to encode video for iphone with this command

ffmpeg -y -threads 8 -i Input-For-Encoding.mp4 -s 480x272 -aspect 16:9 -r
24 -vcodec libx264 -pass 2 -b 448k -maxrate 752k -bufsize 1504k -g 24 -vpre
iphone -f mp4 -acodec libfaac -ac 2 -ar 44100 -ab 96k 01-iPhone.mp4

but why this error occurs as *files for 'iphone' not found*.
what causes a message like the above?
Please fellow friends can help me
thank you