PHP will not execute command if warning appears.

[styler2go]

I ran into a bug where the execution of youtube-dl was aborted because one message was not run in stdout. The solution i used is adding ">> msg.log 2>> msg.log" to the end of the line.

More about the problem:
http://stackoverflow.com/questions/32935064/php-exec-output-does-not-return-and-execute-commands

[dstftw]

It's not a youtube-dl issue if it works fine without PHP.
Warnings you've disabled with --no-warnings are written to strerr, most likely your PHP code is unable to handle this properly.