Oh god.
No.
The truth is as GrimyHR said.
Decoding of a video stream can be done:
- By hardware, ie by the GSP chip. In such case, the chip can decode smoothly anything it has been crafted for, almost independently from the CPU/GPU power. To add new formats, you need to change the chip (ie you can't). The N9's DSP can do h264 decoding up to 720p base profile, and nothing more, it is written in its specs.
- By software, ie using a codec. In such case, you are limited by CPU power. A dual core 1.5GHz Atom CPU cannot even handle 720p, so there's no way you will get the N9 CPU to do it (nor any other embeded ARM soc probably). With the good codecs, the N9 could display HD videos, but certainly not above 5 fps, which would make it completely useless.

Conclusion: no 1080p video on the N9, end of discussion.