If you export a Google VR project the volume keys on the phone do not work in 4.13.1
Example blank project with nothing but a music file on loop on begin play: http://s000.tinyupload.com/index.php?file_id=16827457549232655196
To reproduce:
- Export project to device and try to adjust the volume.
Answerhub query here: [4.13.1] Unable to adjust volume with Google VR - AnswerHub - Unreal Engine Forums