FFmpeg converting to flv but with 0 file size

I’m having problems regarding conversion of video to flv format. Below is my command

for conversion, but it seems to convert the video to flv but the file size remains 0

KB, what could be the problem, please suggest.

My command:

$command =$ffmpegPath . " -i " . $srcFile . " -ar " . $srcAR . " -ab " . $srcAB . "

-f flv -s " . $srcWidth . “x” . $srcHeight . " " . $destFile . " | " . $flvtool2Path

. " -U stdin " . $destFile;

Please Help me ASAP. It’s urgent

Thanks in advance

Regards
Hem