Why would you think that using a hash is overkill? I think that most would agree that it is the way to go. And you can just do:

my %quicktime_ext = map { $_ => undef } qw(...);
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so you dont really need to rework your list.

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As for using the array, you'll have to check each element until you find the one you're looking for or until you get to the end of the list. Heres a way without foreach:

my $found = '';
# overparenthesised for clarity and laziness :)
map { $found || ($found = ($ext eq $_)) } @quicktime_ext;
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Of course map is effectively the same as foreach