YouTube previously offered a specialized way of embedding playlists -- called this "Custom Player." Google today announced of taking away the ability to create new Custom Players.
Google says that "Custom Player never saw a great deal of usage, and we recently removed support for the creation of new Custom Players. If you've already created a Custom Player and have it embedded on your site it should continue to work as-is; the only thing that has changed is that new Custom Players cannot be created."
One common concern is that owners cannot update the videos featured in existing Custom Players. "We recommend that you update the associated playlist to reflect the videos that you would like to feature in the Custom Player, or embed a new playlist."
"While we'll not allow for the creation of new custom players at this time, similar functionality is available through creating embedded playlists, which can be accessed by visiting My Playlists, clicking Share, and then using the embed code given there," Google added.
[Source: YouTube API blog]