How can I transfer a downloaded YouTube video to my iPhone?

i downloaded a YouTube Video and try to transfer it to my Iphone, but it failed every time, whats happening? or:i downloaded a YouTube Video and try t

i downloaded a YouTube Video and try to transfer it to my Iphone, but it failed every time, what's happening?

or:i downloaded a YouTube Video and try to transfer it to my Iphone, but it failed every time, what's happening?

or:What's the video format? if it is not be supported by iPhone, you can use the 4Media YouTube video converter to convert the format then directly transfer it to iPhone.

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