Firstly, I've spent the week googling and trying variations of dozens and dozens of answers for Unix, but it's been a complete bust, I need an answer for Windows, so this is not a duplicate question of the Unix equivalents.
We're trying to create a scheduled task that will process a queue of tasks in PHP, and maintain an array of up to 10 ffmpeg instances at a time. I've tried exec, shell_exec and proc_open , coupled with/without start /B without any "complete" luck.
I'm also quite certain that it has to do with setting up the descriptorspec and pipes (which I'm completely unfamiliar with), and here's why:
Per https://trac.ffmpeg.org/wiki/PHP,
The part that says ">/dev/null" will redirect the standard OUTPUT (stdout) of the ffmpeg instance to /dev/null (effectively ignoring the output) and "2>/dev/null" will redirect the standard ERROR (stderr) to /dev/null (effectively ignoring any error log messages). These two can be combined into a shorter representation: ">/dev/null 2>&1". If you like, you can ?read more about I/O Redirection.
An important note should be mentioned here. The ffmpeg command-line tool uses stderr for output of error log messages and stdout is reserved for possible use of pipes (to redirect the output media stream generated from ffmpeg to some other command line tool). That being said, if you run your ffmpeg in the background, you'll most probably want to redirect the stderr to a log file, to be able to check it later.
One more thing to take care about is the standard INPUT (stdin). Command-line ffmpeg tool is designed as an interactive utility that accepts user's input (usually from keyboard) and reports the error log on the user's current screen/terminal. When we run ffmpeg in the background, we want to tell ffmpeg that no input should be accepted (nor waited for) from the stdin. We can tell this to ffmpeg, using I/O redirection again "
echo "Starting ffmpeg...\n\n";
echo shell_exec("ffmpeg -y -i input.avi output.avi </dev/null >/dev/null 2>/var/log/ffmpeg.log &");
echo "Done.\n";
This example actually uses shell_exec, though we want to use proc_open so that we can use a loop to check if the process has completed or not.
Here's a basic sample loop of what I've tried. The problem in executing this is that the actual ffmpeg processing completes, but the process is hung "waiting for something". When I use debugging, and step out of the loop and terminate the process after a few minutes, the ffmpeg output is written and the script carries on. (From the command line, ffmpeg takes less than a minute to complete)
$descriptorspec = array(
array('pipe', 'r'),
array('pipe', 'w'),
array('pipe', 'w'),
);
$pipes = null;
$cwd = null;
$env = null;
$process = proc_open('start /B ffmpeg.exe -i input.mov output.mp4 -nostdin', $descriptorspec, $pipes, $cwd, $env);
$status = proc_get_status($process);
while($status['running']) {
sleep (60);
$status = proc_get_status($process);
}
proc_terminate($process);
Also, as documented at ffmpeg Main-options:
Enable interaction on standard input. On by default unless standard input is used as an input. To explicitly disable interaction you need to specify
-nostdin.
The -nostdin option seems to indicate that it addresses my problem, but it has no apparent affect. In all solutions for Unix that I've found, it appears to still require some form of this this unix added: </dev/null or 2>&1.
So, with that somewhat exhaustive prologue, can someone explain how to properly configure the proc_open function to satisfy how ffmpeg.exe interacts with I/O? If there is a better or more appropriate approach, I'm happy to do that, but the important thing is to be able to loop thru an array of processes to check if they're complete, so that other faster processes can complete in the meantime.
UPDATE
After exhaustive R&D, it seems that the I/O is not the issue in making this happen (the -nostdin option seems to work as advertised). The premise of my design was to use proc_get_status() to determine when ffmpeg was finished. The flaw in that approach is that apparently that does NOT return the actual PID of the ffmpeg process...it returns the parent PID. So, when proc_get_status() returned that the video conversion was complete, it was in fact still running, not hung. This was further complicated by testing on larger video files. The larger the video, the longer the "residual" time was that it took to actually finish -- the I/O wasn't the issue - watching the Parent PID instead of the child PID was the problem. So, without getting into much lower level system internals with Windows, this doesn't appear to be possible with PHP directly. I've decided to abandon this approach, but hopefully this discovery will save someone else some time and trouble.
