Adding subtitles to video with mencoder

I added some code in video_convertion.php file to add subtitles to videos during convertion. I use the following code but I cannot align the subtitle to the right. Do you know how can I do it? With this code the subtitle is aligned to the bottom-centre of the video:


$cmd_mencoder = "$config[mencoder] '$video_src' -o $video_flv -of lavf -oac mp3lame -lameopts abr:br=56 -ovc lavc -lavcopts vcodec=flv:vbitrate=500:mbd=2:mv0:trell:v4mv:cbp:l ast_pred=3 -srate 22050 -ofps 24 -vf harddup -font /home/user/public_html/include/settings/verdana.ttf -sub /home/user/public_html/include/settings/videosubtitles.srt -ffactor 0.75 -subfont-text-scale 2.5 -subfont-osd-scale 3 -subalign 2 -subpos 98 -spuaa 20";

Thanks for help,
Guillem