You’ll probably need to install your own ffmpeg-php.
It’s a bit of a drama, but it can be done
You can follow the link Scott provided to get you on your way to forming a script to install the packages required to get it all up and running. One thing to keep in mind - add AUTOMAKE and AUTOCONF to the beginning of those Advanced PHP Install scripts.
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How To Install PHP.INI / ionCube on DreamHost