The Google Daydream team has posted an in-depth technical review of the Equi-Angular Cubemap technique they developed for streaming higher quality VR video.
In the post, "Bringing Pixels Front and Center in VR Video", Daydream engineer Chip Brown describes the challenges of streaming 2D videos in a bandwidth constrained VR world, the history of projection, and a description of the Equi-Angular Cubemap technique. Ultimately the algorithm leads to a marked visual improvement over the equirectangular projection traditionally used for 360 video.
From the post:
The traditional cubemap has samples of varying length depending on the sample