The question implicates that you (opposite to the majority) realize that when you detect on just the extention, that you're not checking mime type.
In HTML5 you can use the accept attribute:
<input type="file" accept="video/*" />
You could use multiple (commaseperated?) values.
But the specification says space-seperated, but in reality I only see comma-seperated values.
Mind: in HTML5 capable browsers adding more validation is redundant.
But in case your question related to other use (like drag/drop file uploads), then you could use javascript in stead of jquery:
if(!(file.type.indexOf('video/') == 0)) {
alert('nope');
return false;
}
Needless to say is that you also should validate on the server side.