take video snapshot from ffmpeg on other server in php

I use ffmpeg for take video snapshot.
It works correctly in localhost but when video is on other host it does not work correctly and don't show error.

This is my code.

$videos_file_name='http://test.com/test.mp4'
$cmd = "ffmpeg -i $videos_file_name -an -y -f mjpeg  -ss 00:00:04 -vframes 1 source/$image_file";
return exec($cmd);