针对未知问题的PHP和FFMPEG建议/解决方案

Question

I am having a live video streaming website and I allow people to upload all the video files to the site till now everything is ok.

What I am doing is that I am using FFMPEG to convert the video to mp4 and also get a image out of the video after 20 seconds.

The code that I am using is that:

 require 'vendor/autoload.php';
        $getEXT_check=substr(@$_FILES['profileimage99']['name'],-3);
        if($getEXT_check !='mp4' && $getEXT_check !='MP4'){
        exec('ffmpeg -i '.$uploadfile.' -f mp4 -s 896x504 '.$new_flv.''); }
        //execute ffmpeg and create thumb
        exec('ffmpeg  -i '.$uploadfile.' -ss 00:00:20 -vframes 1  '.$new_image_path);
        $theduration=exec('ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 '.$uploadfile.' 2>&1');
        $theduration_val=round($theduration/60, 2);

What issue I am having is that

1. sometimes the code dosent extract the image out of video
2. video conversation takes very long time for non mp4 video (I am not converting mp4 videos)

Some info what I have done on server. During the development of site I installed ffmpeg on my pc and downloaded the vendor directory by composer.json file. But I have not done these things on my server I have a dedicated server from bluehost and have ffmpeg installed at this location.

/usr/local/bin/ffmpeg
/usr/local/bin/mplayer
/usr/local/bin/mencoder
/usr/bin/flvtool2
/usr/local/bin/MP4Box
/usr/local/bin/yamdi

During uploading the site what I did is that I also uploaded the vendor directory and all the files and made the site live. I haven't used any of the path as given by my server admin after asking.

Please suggest me something where I am doing wrong.