PHP exec - echo output line by line during progress

Question

I'm trying to find a way in which I can echo out the output of an exec call, and then flush that to the screen while the process is running. I have written a simple PHP script which accepts a file upload and then converts the file if it is not the appropriate file type using FFMPEG. I am doing this on a windows machine. Currently my command looks like so:

$cmd = "ffmpeg.exe -i ..\..\uploads\\".$filename." ..\..\uploads\\".$filename.".m4v 2>&1";
exec( $cmd, $output);

I need something like this:

while( $output ) {
    print_r( $output);
    ob_flush();  flush();  
}

I've read about using ob_flush() and flush() to clear the output buffer, but I only get output once the process has completed. The command works perfectly, It just doesn't update the Page while converting. I'd like to have some output so the person knows what's going on.

I've set the time out

set_time_limit( 10 * 60 ); //5 minute time out

and would be very greatful if someone could put me in the right direction. I've looked at a number of solutions which come close one Stackoverflow, but none seem to have worked.

Marc B · Accepted Answer · 2014-03-31 16:04:15Z

1

exec() is blocking call, and will NOT return control to PHP until the external program has terminated. That means you cannot do anything to dump the output on a line-by-line basis because PHP is suspended while the external app is running.

For what you want, you need to use proc_open, which returns a filehandle you can read from in a loop. e.g.

$fh = proc_open('.....');
while($line = fgets($fh)) {
    print($line);
    flush();
}

answered Mar 31, 2014 at 16:04

Marc B

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dhein · Accepted Answer · 2014-12-16 09:08:40Z

1

Since the exec call is a blocking call you have no way of using buffers to get status.

Instead you could redirect the output in the system call to a log file. Let the client query the server for progress update in which case the server could parse the last lines of the log file to get information about current progress and send it back to the client.

edited Dec 16, 2014 at 9:08

dhein

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answered Dec 16, 2014 at 8:42

Muran

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Comments

Kryten · Accepted Answer · 2014-03-31 16:10:43Z

There are two problems with this approach:

The first is that, as @Marc B notes, the fact that exec will block until it's finished. You'll have to devise some way of measuring progress.

The second is that using ob_flush() in this way amounts to holding the connection between server & client open and dribbling the data out a little at a time. This is not something that the HTTP protocol was designed for and while it might work sometimes, it's not going to work consistently - different browsers and different servers will time out differently. The better way to do it is via AJAX calls: using Javascript's setTimeout() function (or setInterval()), make a call to the server periodically and have the server send back a progress report.

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