If it's the version downloaded from this thread (Big Blue Button on top) then it's developer's fault as the command is wrong.
PHP API\New API Version\musictok\app\Lib\Regular.php lines 310 and 332
for you to check if they are called or not and what's the error add this before the last quote
>> /var/log/video_gif.log 2>&1
and
>> /var/log/video_thumb.log 2>&1
like this
PHP:
// Line 310
$gif = "ffmpeg -ss 3 -t 2 -i $original_video_file_path -vf 'fps=10,scale=100:-1:flags=lanczos,split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse' -loop 0 $genrateGifPath >> /var/log/video_gif.log 2>&1";
// Line 322
$thumb_cmd = "ffmpeg -i $original_video_file_path -vf fps=3 $thumb_path >> /var/log/video_thumb.log 2>&1";
I can bet the error you will see in the log would be like: "cannot find $original_video_file_path" or something similar
Your choice. My time is totally limited. Maybe you'll find someone else to help you then.