Can I edit a video on youtube in my phone or computer?

https://addons.mozilla.org/en-US/firefox/addon/video-downloadhelper/versions/

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http://www.videosoftdev.com/free-video-editor

There is a separate section of video editing in You Tube itself where you can directly edit the video. Mashable had explained it here: http://mashable.com/2012/10/19/youtube-video-editing/

If all you want to do is let people see the part of the video you’re in, you can actually do that without any editing at all. Go to your video and pause the video wherever your interview starts, click on the YouTube “share” tab below the video, then check the radio button reading “start at”. It’ll give you a URL to send which starts the video at whatever point you’ve paused it at. (All it does is append a ”?t=x” to the end of your URL, where x is the number of seconds into the video where you’ve paused, so you can do it manually too.)

There are some facilities with youtube to edit videos online. But it has very few features.
Best way is download it and edit.