featured a total of six episodes per week, though all future installments would air three nights per week. Of these three episodes, the weekly eviction episode is the only one that is live; this is the only episode to feature host Julie Chen. This show generally airs on Thursdays. To date, there have been a total of 820 episodes of the series to air. With the exception of the ninth season, the series typically airs once a year during the summer season. The first 15 seasons aired in standard definition, with the 16th season being the first to be produced in HD. However, the live internet feeds would not broadcast in HD until Big Brother 17. Before the series made the transfer, it was the last remaining regularly scheduled prime-time series to remain in standard definition. CBS released the entire third season as a nine-disc set on Region 1 DVD. This made it the first season to receive an official release, and has since become a rare item to find. The fourth season saw the release of a two-disc highlights DVD, featuring previously unseen footage deemed too racy for the main broadcast. To date, these are the only seasons to see a physical release. Beginning with the seventh season, all future seasons are available for purchase on digital retail sites. With the 15th season, TVGN (now Pop) began airing re-runs of the series at later dates, making it the first season to be aired following its premiere; this continued with the 16th season. Subscribers to CBS All Access are able to stream the complete run of Big Brother—including the differently-formatted first season—and an episode of Big Brother 2 that did not air in most markets due to ongoing coverage of the September 11 attacks. CBS aired the spin-off series Celebrity Big Brother from February 7–25, 2018. It was the first spin-off to air on the broadcast network and the second season overall to air in the winter television season (the other being season 9). The celebrity edition aired in a concentrated run with fewer episodes, but with multiple episodes each week. Live Internet feeds One of the main aspects of the series is the live feeds, in which viewers can view inside the house at any time. The live feeds have been a part of the series since its inception, initially being offered as a free service during the first