This is a Heroku buildpack for using ffmpeg in your project.
$ heroku buildpacks:add https://github.com/tastemade/heroku-buildpack-ffmpeg
You can verify installing ffmpeg by following command.
$ heroku run "ffmpeg -version"
If you want to use your own ffmpeg binary, fork and rewrite following line.
https://github.com/tastemade/heroku-buildpack-ffmpeg/blob/master/bin/compile#L10