I'm testing a jekyll you tube plugin I found here. It runs well on local preview:
$ jekyll server
but after I push it on github I received a Page build failure email.
A fast search and I found that github pages does not support unsafe plugins.
Before push your new post to github is a good practice to build you site in safe mode and check for errors:
$ jekyll build --safe
Of course in that case the plugin is really unnecessary so I've removed the plugin and add the html code myself as suggested by gitthub.
Here is the result, my "little" sister playing for Lucca Philharmonic Orchestra: