The Alliance for Open Media, according to its website, was formed to "define and develop media codecs, media formats, and related technologies to address marketplace demand for an open standard for video compression and delivery over the web."
The Alliance is developing a royalty-free video codec known as AOMedia Video 1 (AV1), which is designed to compress video before it's stored or sent over a network. Apple's move to join the Alliance for Open Media is notable because implementing such technology requires it to be widely supported, and Apple was one of the only major companies not participating.
AV1 continues to be a work in progress, with the Alliance for Open Media planning to release the first version of in the near future. Mozilla supports an early version of AV1 and has said that it reduces file sizes by 25 to 35 percent compared to HEVC, which Apple implemented support for in macOS High Sierra and iOS 11.
Other members of the Alliance for Open Media include Amazon, Cisco, Facebook, ARM, Google, IBM, Intel, Microsoft, Mozilla, Netflix, Hulu, NVIDIA, and more.