I think -1c is correct. The reason it wasn't playing the most recent video was because 30 seconds wasn't long enough of a delay for the video to begin downloading.
cd /media/mmc1/Videos FILE=`/bin/ls -1t |head -1` youtube-dl-x --no-part -f 5 -o "%(stitle)s.%(ext)s" `xclip -out` & sleep 5 while [ "$FILE" = "`/bin/ls -1t |head -1`" ]; do sleep 5 ; done sleep 30 mplayer `/bin/ls -1t |head -1`