Submitted by Thibault Saunier @thiblahute

Link to original bug (#757684)

Description

We should offer high level APIs for common purposes, so I am adding one for transcoding.

I also implemented 2 elements to make everything more reusable:

• uritranscodebin: A equivalent to playbin, where the user just has to specify 1 source URI, 1 destination URI and the wanted encoding target
• transcodebin: A bin that will plugin decodebin [! some filters] ! encodebin.