Adding a video to Agency Theme's Portfolio?

How do i Add a youtube video Embed in (frontmatter) Yaml?, please help

Iam using the Agency theme and i want to create a portfolio with video embeded from youtube

title: Portfolio
menu: portfolio
portfolios:
-
title: Dreams
subtitle: 'Website Design’
layout: default
modalid: 1
date: 1405641600
img: dreams.png
thumbnail: dreams-thumbnail.png
alt: image-alt
projectdate: 'April 2014’
client: 'Start Bootstrap’
category: 'Web Development’
description: ‘Lorem ipsum dolor sit amet, usu cu alterum nominavi lobortis. At duo novum diceret. Tantas apeirian vix et, usu sanctus postulant inciderint ut, populo diceret necessitatibus in vim. Cu eum dicam feugiat noluisse.’
-