How to get rid of the black bands of my video?

Important note: this method only works for videos uploaded to YouTube before June 2016

If the element selected for our video has quite a different proportion (width/height ratio) of our video, YouTube will show black bands around our video, as in:

To avoid that effect, YouTube sometimes accepts tags to tell it how to zoom in or crop the video to avoid the bands.

The official YouTube documentation for this feature is located at https://support.google.com/youtube/answer/146402?hl=en-GB&authuser=1

These are the tags available:

• yt:crop=16:9zoom the video to cover a 16:9 proportion, probably losing some zones
• yt:stretch=16:9stretch the video to cover a 16:9 proportion, probably deforming it
• yt:stretch=4:3zoom the video to cover a 4:3 proportion, probably losing some zones

We will type these tags on the YouTube video manager: