Chromecast is a line of digital media players developed by Google. Designed as small dongles, the devices play audio/video content on a high-definition television or home audio system by directly streaming it via Wi-Fi from the Internet or a local network. Users select the media to play using mobile apps and web apps that support the Google Cast technology. Alternatively, content can be mirrored from the Google Chrome web browser running on a personal computer, as well as from the screen of some Android devices. The first-generation Chromecast, a video streaming device, was announced on July 24, 2013, and made available for purchase on the same day in the United States for US$35. The Google Cast SDK was released on February 3, 2014, allowing third parties to modify their software to work with Chromecast. According to Google, over 20,000 Google Cast–ready apps are available, as of May 2015.Chromecast was favorably received by critics, who praised its simplicity and potential for future app support. Over 20 million units have shipped globally since launch, and it was the best-selling streaming device in the United States in 2014, according to NPD Group. Since Chromecast's launch, it has handled more than 1.5 billion stream requests. A second-generation Chromecast and audio-only model called Chromecast Audio were announced in September 2015.