FFMPEG with PHP- Output File Is Null

If anybody has done any work with FFMPEG and could help me, it would be
GREATLY appreciated...

Using a Linux VPS (Apache) and with FFMPEG properly installed (the code
works perfectly from SSH command line).

The following code is supposed to use FFMPEG and FLVTOOL to copy an .mpg to
..flv

From the command line, it works fine- exactly as expected. From PHP script,
it will create the .flv file, but not write any data to it.

Any ideas?

Thanks!