A way to save 360° panorama video
I would be tempted to use a solution which involves decoding a single rectangular video stream so you don't need any special video decoder. As you have said there will be performance penalties for decoding multiple seperate streams. 

Something like octohedran cube maps might be a good offline way to convert 6 video streams into a single video stream while minimizing distortion. A relatively cheap pixel shader can be used to project the 'cube' map back to camera space.

Further reading here > http://www.vis.uni-stuttgart.de/~engelhts/paper/vmvOctaMaps.pdf