Hi,

please find attached a patch (relative to FFmpeg master as of early January 10, 2023)
adding avfilter support for extended perceptually weighted peak signal-to-noise ratio
(XPSNR) measurements for videos, as described in the related addition to filters.texi.

The XPSNR code was originally vectorized using SIMD intrinsics, but we concluded that
FFmpeg code requires asm instead of such intrinsics, so we let gcc auto-convert these
instructions to pure assembly; see the vf_xpsnr.asm file. If the added asm code is too
lengthy, intrinsics would be possible, or something else is missing, please let us know.

Best,

Christian Helmrich and Christian Stoffers
Fraunhofer HHI