With the first code I get the following error:
Server said cmd = ffmpeg -y -i /www/htdocs/silvertest/http/assets/Uploads/video-11.flv -an -s 640x480 -ss 10 -an -r 1 -vframes 1 -y -vcodec mjpeg -f mjpeg /www/htdocs/silvertest/http/assets/video_thumbnails/video-11.jpg, descriptorspec = Array, and pipes = Array
With your second code in _config.php I get the following error:
Warning: proc_open() has been disabled for security reasons in /www/htdocs/silvertest/http/mysite/_config.php on line 34
Finally a readable PHP error message.
So it is actually a server setting...
I presume there's no simple .htaccess config line to enable proc_open(), right? Or an alternative to that function?
Tomorrow I'll contact my hosting provider to discuss this topic.
Thanks again man!