H.264, H.265, VP6
For the last 10 years, H.264/AVC has been the dominant video codec used for streaming but with Apple adopting H.265/HEVC in iOS 11 and Google heavily supporting VP9 in Android, a change is on the horizon. Next year the Alliance for Open Media will release their AV1 codec which will again improve video compression efficiency even further. But the end result is that the codec market is about to get very fragmented, with content owners soon having to decide if they need to support three codecs (H.264, H.265, and VP9) instead of just H.264 and with AV1 expected to be released in 2019. As a result of what's take place in the codec market, and with better quality video being demanded by consumers, content owners, broadcasters and OTT providers are starting to see a massive increase in encoding costs. New codecs like H.265 and VP9 need 5x the servers costs because of their complexity. Currently, AV1 needs over 20x the server costs.
High Efficiency Video Coding (HEVC), also known as "H.265" and "MPEG-H Part 2", is a video compression standard, one of several potential successors to the widely used AVC (H.264 or "MPEG-4 Part 10"). Wikipedia.
The licensing fees are one of the main reasons HEVC adoption has been low on the web and is why some of the largest tech companies (Amazon, AMD, ARM, Cisco, Google, Intel, Microsoft, Mozilla, Netflix, Nvidia, and more) have joined the Alliance for Open Media, which aims to finalize the royalty-free alternative video coding format "AV1" by the end of 2017. Wikipedia.