title: Add metadata to flv files with ffmpeg instead of flvmdi
body: <p>I have made a player for stream flv movies in flash with netstream but it needs some metadata information named " keyframe " containing two array of times and positions , some flv videos have this meta data and some not , i could add the keyframe metadata with  a program named "flvmdi" and player worked properly , but i can`t install this software on my server for some reasons. 
  I know that we can add metadata to a movie with ffmpeg function in PHP .
  Can i use ffmpeg function in PHP to add keyframe arrays as metadata to flv file?
  How can we make times and positions arrays to inject to a flv file with ffmpeg in php?</p>