SSIMPLUS is a commercial perceptual quality metric, originally from SSIMWAVE and now part of IMAX, designed to estimate quality the way a viewer would perceive it across different devices - the cross-device angle is its distinguishing claim, predicting how the same encode looks on screens from a phone to a large television. It belongs to the family of file-based QC suites: products that bundle perceptual scoring with hundreds of broadcast conformance checks (right codec, right loudness, no black frames, valid captions), a graphical interface, dashboards, and a support contract, aimed at delivery workflows and non-engineer operators. The catch, common to this whole family, is that you are not paying for better math but for the wrapper, the scale, and the support; and SSIMPLUS reports its own proprietary score that is not VMAF, so it cannot be read on the same ruler. Open-source FFmpeg with libvmaf computes a free perceptual number; a suite is worth buying when compliance, live monitoring, or an operator makes the wrapper worth it.
