my $content_length = $end - $begin;

print "Content-Type: text/html \r\n";
print "Content-Type: application/x-vlc-plugin \r\n";
print "Cache-Control: public, must-revalidate, max-age=0 \r\n";
print "Pragma: no-cache \r\n" ;
print "Accept-Ranges: bytes \r\n";
print "Content-Length: $content_length", "\r\n";
print "Content-Range: bytes $begin-$end/$size \r\n";
print "Content-Disposition: inline; filename=\"$name$ext\"\r\n";
print "Content-Transfer-Encoding: binary\r\n";
print "Connection: close\r\n";
[download]

Whenever you see "internal server error", that just means that the real error is in the web server error log.

Why are you "not sure about this" anyway? When you run the program outside of the web server, Perl will show you the output of your program and also errors if it finds them. Do you know how to run your program outside of the web server?

Note that HTTP headers conventionally do not have whitespace before the line breaks. Instead of

print "Content-Type: text/html \r\n";
[download]

you should write:

print "Content-Type: text/html\r\n";
[download]

(without the space before the \r\n)

yeah i executed the program in the terminal. here is the output of that

Content-Type: text/html
Content-Type: application/x-vlc-plugin
Cache-Control: public, must-revalidate, max-age=0
Pragma: no-cache
Accept-Ranges: bytes
Content-Length: 128959310 
Content-Range: bytes 0-128959310/128959310
Content-Disposition: inline; filename="lua.mp4"
Content-Transfer-Encoding: binary
Connection: close
[download]

In the error log it is writing

Premature end of script headers: download.cgi
[download]