Great to see the band back together again! Washington Post, which notes one of the purposes of this video is to troll Trump (too easy):

Joe Biden’s presidential campaign on Wednesday deployed a new tactic to reach voters when bunting-strewn stages and boisterous rallies have been set aside: using cinematic flourish to tease a major appearance with Barack Obama intended to excite Democrats and troll President Trump with the presence of his popular predecessor.

Biden faces an urgent need to expand his digital presence in a campaign now likely to be defined to a great degree online, and will use the event — to be fully released on social media Thursday morning — as a way to reach Obama’s nearly 121 million Twitter followers. It leans on the former president’s stature and signature coolness — in the view of many voters Biden needs — to add sparkle as the campaign slogs through summer.

The video is also a sign of how much Biden and his team will focus on his partnership with Obama even as he goes through the process of searching for his own running mate.