I got today a warning video in a YouTube sprout, that the old API will drop:

In early May, Data API v2 video calls will start returning only the warning video introduced on April 20. Users will not be able to view other videos on apps that use the v2 API video calls. See youtube.com/devicesupport for affected devices.

By late May, v2 API calls except for comments and captions will receive 410 Gone HTTP responses.

http://youtube-eng.blogspot.de/2015/04/bye-bye-youtube-data-api-v2.html