Description:
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i want to convert a video file of any extension to a flv extension (flash extension) and save it in a specific folder. i used the execute function built in php (exec[command]) to run a command to do that but it didn't work. i don't know why. so please help me to fix this error.

Reproduce code:
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if($config[vresize] == 1) {$encodecommand="$config[mencoder] $config[vdodir]/$vdoname -o $config[flvdodir]/".$vid."x.flv -of lavf -oac mp3lame -lameopts abr:br=56 -ovc lavc -lavcopts vcodec=flv:vbitrate=$config[vbitrate]:mbd=2:mv0:trell:v4mv:keyint=10:cbp:last_pred=3 -lavfopts i_certify_that_my_video_stream_does_not_use_b_frames -vop scale=$config[vresize_x]:$config[vresize_y] -srate $config[sbitrate]";
  }else {
    $encodecommand="$config[mencoder] $config[vdodir]/$vdoname -o $config[flvdodir]/".$vid."x.flv -of lavf -oac mp3lame -lameopts abr:br=56 -ovc lavc -lavcopts vcodec=flv:vbitrate=$config[vbitrate]:mbd=2:mv0:trell:v4mv:keyint=10:cbp:last_pred=3 -lavfopts i_certify_that_my_video_stream_does_not_use_b_frames -srate $config[sbitrate]";
  }
if(exec("$encodecommand")) {
  //update flv metatags
  exec("flvtool2 -Uv $config[flvdodir]/".$vid."x.flv $config[flvdodir]/".$vid.".flv");
  exec("$config[metainject] -Uv $config[flvdodir]/".$vid."x.flv $config[flvdodir]/".$vid.".flv");

Expected result:
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convert any video file from its extension to .flv extension and move it to a flvdir folder.

Actual result:
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didn't executed at all.