This is the traditional bugle call known as "To The Colours". The call is particularly associated with US forces and used as a mark of respect for the National Flag during ceremonial occasions. See also the bugle call known as Retreat which is also associated with the flag. See the links at the left to download the sheet music or audio files. More bugle calls are listed in our article about the history and cultural impact of Bugle Calls
The image below is the first page of the sheet music, and here you can download the full sheet music for To The Colours (bugle call) in PDF format.