Jabhat Al-Nusra's video is published by Al-Manarah which publishes official Al-Qaeda videos from around the world. Officials from the US Department of State and US intelligence agencies have said that the group is a front for Al-Qaeda. The group was previously unknown, but their tactics and black flags immediately drew attention to Al-Qaeda, and as early as Febuary 16, US spy chief James Clapper warned that they appear to be front for Al-Qaeda infiltrating Syria from Iraq. However, the Department of State has officially been slow over the Al-Qaeda issue in Syria. This would appear to be a realisation of the contradiction of calling for the overthrow of the Syrian government and arming terrorists. On numerous times state officials have confirmed their knowledge of many aspects of the problem, including the travelling of Iraq Al-Qaeda to fight in Syria. For example see http://www.cbsnews.com/8301-202_162-57483500/state-dept.-al-qaeda-in-iraq-fighting-in-syria/

The US officials also confirm that Al-Qaeda has a serious foothold in Syria, for example see http://www.ynetnews.com/articles/0,7340,L-4267086,00.html

The group known as Jabhat Al-Nusra is a part of the the alliance of militias and foreign mercenaries known as the 'Free Syrian Army'. It does not have a structure like a real army, and lacks command. They have been responsible for some of the most brutal suicide bombings massacring civilians randomly in residential areas. Al-Nusra consider themselves part of the 'Free Syrian Army', for example see

http://www.liveleak.com/view?i=218_1343091168

Holy Shit! Interview With Al-Qaeda Boy Soldier Of 'Free Syrian Army' In Aleppo