Unable to call exec in PHP to run video conversion

You cannot call exec to run video conversions in PHP.
I upload a user video to the server and then run exec to perform the ffmpeg operation, but the FFmpeg command: For example, under CMD. Running Ffmpeg-i 1.avi 2.flv is normal, but when you exec in PHP ("Ffmpeg-i. /1/1.avi. /1/1.flv "); When you do not see the converted file. Should be an execution failure. How do I call ffmpeg this external command????
------Solution--------------------
.. /1/1.avi. /1/1.flv

What is this? Path? Make sure the path is correct.
------Solution--------------------
EXEC ("Ffmpeg-i. /1/1.avi. /1/1.flv "); Instead of trying to be absolutely the path.

For example:
$source = DirName (dirname (__file__)). " /1/1.avi ";
$dest = DirName (dirname (__file__)). " /1/1.flv ";
EXEC ("Ffmpeg-i". $source. " ". $dest);

