Hi10P is an H.264 video codec profile that is used most often for encoding anime videos. Hi10P is short for High 10 Profile and atop H.264's High Profile there is support for 10-bits per sample of decoded picture precision.
Hi10P generally has to be software-decoded with the CPU using modestly-powered hardware, but published this week for Mesa was a OpenMAX Gallium3D state tracker. While there's already the VDPAU state tracker for Gallium3D, AMD worked out the OpenMAX state tracker and one of its benefits over the VDPAU implementation is being able to decode Hi10P content using the UVD video decode engine on Radeon GPUs.
The VDPAU state tracker doesn't support Hi10P decoding currently, but an open-source developer is looking to make that happen. Peter Frühberger looked at the OpenMAX state tracker and found that just two fields are missing to also decode Hi10P with VDPAU on UVD, so he's hoping to get the upstream UVD API bumped to support the additional fields as part of the H.264 support.
Those interested in Hi10P can find more information on the current plan via this mailing list post.