php video upload and ffmpeg won't create a thumbnail

I am trying to make a video upload feature for my project. But I have a problem with ffmpeg section. ffmpeg is already installed on my server. But i can not get any thumbnail. I have try to create thumbnail using the following ffmpeg code:

$videoa = exec("/usr/bin/ffmpeg  -i $videoUrlp.flv -f flv -s 650x390 $videoUrlp.mp4 2>&1");
$videob = exec("/usr/bin/ffmpeg  -i $videoUrlp.mp4 -vcodec png -ss 00:00:5 -s 650x390 -vframes 1 -an -f rawvideo $videoUrlp.png");

But i ge this when use var_dump(); for var_dump($videoa); and var_dump($videob);

string(74) "https://mywebsite.com/uploads/video/ey1kXNew_video.flv: Input/output error" string(0) ""

Also if i use the shell_exec like this:

$videoa = shell_exec("/usr/bin/ffmpeg  -i $videoUrlp.flv -f flv -s 650x390 $videoUrlp.mp4");
$videob = shell_exec("/usr/bin/ffmpeg  -i $videoUrlp.mp4 -vcodec png -ss 00:00:5 -s 650x390 -vframes 1 -an -f rawvideo $videoUrlp.png");

and the var_dumps() giving me NULL NULL.

What am I missing here please anyone can help me?

And here is my full video upload code:

$valid_formats = array("mp4","MP4","flv");
            if(isset($_POST) and $_SERVER['REQUEST_METHOD'] == "POST") {
               $name = $_FILES['uploading']['name'];
               $size = $_FILES['uploading']['size'];
               if(strlen($name)) {
                   $ext = strtolower(pathinfo($name, PATHINFO_EXTENSION)); 
                   $name = alphaID(microtime(true) * 10000).'_video';
                   if(in_array($ext,$valid_formats)) {
                   if($size<(50024*50024)) {
                      $GetVideoName = $name;
                      $video_ext=$ext;
                       $tmp = $_FILES['uploading']['tmp_name'];
                       if(move_uploaded_file($tmp, $videoPath.$GetVideoName.'.'.$video_ext)) {
                           $videoUrlp = $base_url.'uploads/video/'.$GetVideoName;
                           $videoa = exec("/usr/bin/ffmpeg  -i $videoUrlp.flv -f flv -s 650x390 $videoUrlp.mp4 2>&1");
                           $videob = exec("/usr/bin/ffmpeg  -i $videoUrlp.mp4 -vcodec png -ss 00:00:5 -s 650x390 -vframes 1 -an -f rawvideo $videoUrlp.png");
                           echo var_dump($videoa);
                           echo var_dump($videob);

                        } else {
                            echo "Fail upload folder with read access.";
                        }
                     } else
                        echo "Image file size max 1 MB";                    
                     } else
                        echo "invalidvieo"; 
                 } else
                    echo "Please select image..!";
                 exit;
              }

I have tested also like this way:

echo exec("/usr/bin/ffmpeg -i $videoUrlp.flv -ar 22050 -ab 32 -f flv -s 780x400 $videoUrlp.$video_ext");
echo exec("/usr/bin/ffmpeg -i $videoUrlp.$video_ext -deinterlace -an -ss 1 -t 00:00:05 -r 1 -y -vcodec mjpeg -f mjpeg $videoUrlp.png 2>&1");

and i see the following echo

video:71kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.000000%

and another try then i get this note: https://mywebsite.com/uploads/video/1547892356_video.flv: Connection refused

echo exec("/usr/bin/ffmpeg -i $videoUrlp.flv -ar 22050 -ab 32 -f flv -s 780x400 $videoUrlp.$video_ext");
echo exec("/usr/bin/ffmpeg -i $videoUrlp.$video_ext -deinterlace -an -ss 1 -t 00:00:05 -r 1 -y -vcodec mjpeg -f mjpeg $videoUrlp.png 2>&1");

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