What kind of projections Youtube and Facebook use for VR?

They are both using H.264 video coding standard and MP4 container [1]. But, they have different projections:

Facebook is using the cubemap projection [2].
Youtube is using equirectangular projection [3].


References
[1] Qian, Feng, et al. "Optimizing 360 video delivery over cellular networks." Proceedings of the 5th Workshop on All Things Cellular: Operations, Applications and Challenges. ACM, 2016.
[2] Under the hood: Building 360 video. https://code.facebook.com/posts/1638767863078802.
[3] YouTube live in 360 degrees encoder settings. https://support.google.com/youtube/answer/6396222.

VR Forcast

Virtual Reality (VR) technology is projected to form a big market of $120 billion by 2020 [1].


References
[1] Augmented/Virtual Reality revenue forecast revised to hit $120 billion by 2020. http://goo.gl/Lxf4Sy.

OpenVQ

OpenVQ is an independent implementation of  Perceptual Evaluation of Video Quality (PEVQ) described in ITU-T J.247 [44, Annex B]. Due to patent issues, OpenVQ has not implemented the temporal alignment impairments in PEVQ. OpenVQ is released under the terms of the GNU Affero General Public License (AGPL) version 3.

https://bitbucket.org/mpg_code/openvq

Quality metrics for virtual reality videos

• Quality Metric for Spherical Panoramic Video [1]
• A Framework to Evaluate Omnidirectional Video Coding Schemes [2]
• A perceptual quality metric for high-definition stereoscopic 3D video [3]
• Towards reliable and reproducible 3D video quality assessment [4]

References
[1] Zakharchenko, Vladyslav, Kwang Pyo Choi, and Jeong Hoon Park. "Quality metric for spherical panoramic video." SPIE Optical Engineering+ Applications. International Society for Optics and Photonics, 2016.
[2] Yu, Matt, Haricharan Lakshman, and Bernd Girod. "A Framework to Evaluate Omnidirectional Video Coding Schemes." Mixed and Augmented Reality (ISMAR), 2015 IEEE International Symposium on. IEEE, 2015.
[3] Battisti, F., et al. "A perceptual quality metric for high-definition stereoscopic 3D video." SPIE/IS&T Electronic Imaging. International Society for Optics and Photonics, 2015.
[4] Goldmann, Lutz, and Touradj Ebrahimi. "Towards reliable and reproducible 3D video quality assessment." SPIE Defense, Security, and Sensing. International Society for Optics and Photonics, 2011.

Quality-Bitrate Curve Fitting

It seems that PSNR-bitrate curves can be better modeled via "PSNR = a * log( b * Rate + c)" formula. For SSIM-bitrate, "SSIM = a * (Rate ^ b) + c" seems to work better.