7.1 sound wont play audio on youtube

many videos on Youtube (most of them I would think) are either stereo or mono sound only. You won't get 7.1 (or even 5.1) true surround sound from those.

The source sound has to have been recorded in 7.1 surround sound if you want to hear it like that. Otherwise it will just be mono or stereo, or your hardware will produce "simulated" surround sound if it has that capability.

Basically, you cannot expect get true surround sound out if it doesn't exist in the source media to start with.
That's like expecting to get a colour photograph from black-and-white film (remember those?).
 

thanks for the reply, i forgot to mention that i tried it with 7.1 in internet explore but there it worked?