У вашего броузера проблема в совместимости с HTML5
To use the YouTube Video Editor:
- Log into your YouTube account and then type in https://www.youtube.com/editor
- Get something that you download like iMovie or Windows Movie Maker or even editing in QuickTime
- Upload any clips that you intend to use before you start using it, make them unlisted so that they're not published out to the public
- Drag and drop the clip/s that you want to edit or use
- Trim it by selecting the edge marks and move them in and out to create a new in point
- You can add effects, fix the brightness and contrast
- You can edit it using the play head, hit the scissors icon, you'll see that there's a play head like line, there's a tiny little x arrow or x icon on it, click right in the middle of the clip that will turn it into two clips
- You can also add some music and you can mix it with your original audio and trim to the end of the video
- Hit publish and your video will go live and then you can adjust the settings, add annotations, description and etc
Added resource on how to use the YouTube Video Editor:
From: http://mashable.com/2012/10/19/youtube-video-editing/