Alright my free piece of code for the day.

The video variables are located in index_dl.pm line 609-637.

The two important lines are:

      $file->{video_img_url}="$1/i/$dx/$file->{file_real}.jpg";
      $file->{video_thumb_url}="$1/i/$dx/$file->{file_real}_t.jpg";

Take whatever other variables you need like vid_height, vid_width. They're optional as you don't need these and can hard set them in your template (default is 400x300).

In index.cgi go to line 2934

      $files = $db->SelectARef("SELECT f.*, DATE(f.file_created) as created, 
                                (SELECT COUNT(*) FROM Comments WHERE cmt_type=1 AND file_id=cmt_ext_id) as comments
                                FROM Files f 
                                WHERE f.usr_id=? 
                                AND f.file_fld_id=? 
                                ".&makeSortSQLcode($f,'file_created').$ses->makePagingSQLSuffix($f->{page}),$ses->getUserId,$f->{fld_id});

and replace with:

      $files = $db->SelectARef("SELECT f.*, DATE(f.file_created) as created, s.srv_htdocs_url,
                                (SELECT COUNT(*) FROM Comments WHERE cmt_type=1 AND file_id=cmt_ext_id) as comments
                                FROM Files f, Servers s
                                WHERE f.usr_id=? 
                                AND f.file_fld_id=? 
                                AND f.srv_id=s.srv_id
                                ".&makeSortSQLcode($f,'file_created').$ses->makePagingSQLSuffix($f->{page}),$ses->getUserId,$f->{fld_id});


Go to line 2973:

      $_->{comments}||='';

If you only want video thumbnails then underneath it add:

      if( ($c->{m_v} && $_->{file_name}=~/\.(avi|divx|flv|mp4|wmv|mkv)$/i) )
      {
         my $iurl = $_->{srv_htdocs_url};
         $iurl=~s/^(.+)\/.+$/$1\/i/;
         my $dx = sprintf("%05d",($_->{file_real_id}||$_->{file_id})/$c->{files_per_folder});
         $_->{video_img_url}="$iurl/$dx/$_->{file_real}.jpg";
         $_->{video_thumb_url}="$iurl/$dx/$_->{file_real}_t.jpg";     
      }

If you only want image thumbnails then underneath it add:

      if( ($c->{m_i} && $_->{file_name}=~/\.(jpg|jpeg|gif|png|bmp)$/i )
      {
         my $iurl = $_->{srv_htdocs_url};
         $iurl=~s/^(.+)\/.+$/$1\/i/;
         my $dx = sprintf("%05d",($_->{file_real_id}||$_->{file_id})/$c->{files_per_folder});
         $_->{video_img_url}="$iurl/$dx/$_->{file_real}.jpg";
         $_->{video_thumb_url}="$iurl/$dx/$_->{file_real}_t.jpg";     
      }

If you want to use video and image thumbnails then use:

      if( ($c->{m_i} && $_->{file_name}=~/\.(jpg|jpeg|gif|png|bmp)$/i ) 
          || ($c->{m_v} && $_->{file_name}=~/\.(avi|divx|flv|mp4|wmv|mkv)$/i) )
      {
         my $iurl = $_->{srv_htdocs_url};
         $iurl=~s/^(.+)\/.+$/$1\/i/;
         my $dx = sprintf("%05d",($_->{file_real_id}||$_->{file_id})/$c->{files_per_folder});
         $_->{video_img_url}="$iurl/$dx/$_->{file_real}.jpg";
         $_->{video_thumb_url}="$iurl/$dx/$_->{file_real}_t.jpg";     
      }

Congratulations, you've now got template variables video_img_url and video_thumb_url available in my_files. I've tested this as working.