How reliable are meta tags in videos for user submitted videos?

I'm working on a website that lets users submit video content. I would like to avoid transcoding the submitted video just to get simple statistics such as video duration, so I should be able to use tags on the video.

But how reliable are these? Can I assume that 100% of submitted videos will have accurate duration data in their meta tags? Or is that unlikely and should I instead go to the trouble of transcoding the video just to be sure?

PS: This question doesn't have a single, objectively correct answer. For any downvoters on this question, maybe you could help out by suggesting where this question might be submitted instead! Thanks!