This module can get online .mp4 file's duration

$npm install online_mp4_duration
var onlinemp4duration = require('online_mp4_duration');
onlinemp4duration({url: 'http://example.com/instance.mp4', full_scan: true/false}, function(err, duration){})
full_scan enables you to decide whether it will scan through whole mp3 file if there's no metadata in the first 1MB and the last 1MB

1. this module won't check the url, you need to check user input yourself.
2. I can't have good test .mp4 url, so there may be lots of bugs. Feel free to send PullRequest :D