PHP Internal Server Error 500 when using ffmpeg to convert files

I've a PHP script that it's being called with a cron job in my server to run uploaded video conversions. It works fine for some videos, but when the video is a bit larger (21MB for example) I get a 500 Internal Server Error and no other output.

I think that it's possible that this problem was due to timeouts so I've added set_time_limit(9000) and also ini_set('max_execution_time', 9000) to prevent this, but this does not solve anything.

I execute ffmpeg using:

$cmdOut = shell_exec ('ffmpeg -y -i [....] 2>&1'); // [....] is the rest of the command, it works fine with other videos, so i assume that it works ok.
echo print_r($cmdOut);

However there is no output, and the following lines are not being executed, so after the shell_exec t开发者_运维问答he script is aborted.

Looking at the apache error_log I can see this line:

[Wed Jan 12 00:12:46 2011] [error] [client xx.xxx.xxx.xxx] Premature end of script headers: index.php

But there are no other clues. Can anyone help me?

For testing purposes i've created this PHP script:

<?php
set_time_limit(300);
sleep(120);
echo "SLEEP OUT";
?>

This script causes a "500 Internal Server Error" when i call it from my web browser, so i suppose that set_time_limit is not working. If i put sleep(30) it works and it returns the text SLEEP OUT. So the question is, how can i avoid the timeout error to execute a PHP script that is taking 5 or 10 minutes to complete??

NOTE: Server is CentOS running apache and php as FastCGI module.

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Finally i've solved this on my own. I've developed a workaround to bypass the timeout limitation in php. My solution is to execute the php script using the php-cli command with a scheduled cron job. This way i don't have the time limit when executing my script and it works nicely.

Thanks to all, specially to Phoenix for their time and ideas about this issue.

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Do you really need the console output for anything? I ran into a similar issue once, even though I modified the primary php.ini itself to extend the execution time limit, it would still drop randomly when doing ffmpeg through exec. Wound up having to > /dev/null & it to stop it from dropping execution, then it worked fine regardless of what was thrown at it.