Pandora on Thursday launched Pandora Plus, a replacement for its $5-a-month Pandora One streaming music service. The 4 million Pandora One subscribers will be switched over to Plus, which will continue to offer ad-free listening at the same price. However, Pandora Plus also offers an opt-in video advertising feature that lets users skip or replay songs. Plus also has an offline mode. The service automatically saves the main station a subscriber listens to, as well as the three listened to most recently, for offline access.