FFmpeg is the general-purpose, open-source media tool that decodes, scales, encodes, and pipes frames between filters. In quality measurement it is the engine that reads the encode and the master and feeds frames in matched pairs to libvmaf, the library that actually computes the numbers - so FFmpeg with libvmaf is the default free way to measure video quality, computing VMAF, PSNR, SSIM, and MS-SSIM from one command. It also provides standalone psnr and ssim filters and the command-line interface to encoders like x264, x265, and SVT-AV1. Being scriptable and headless, it is what most teams wire into an automated quality gate. The catches are that libvmaf is a compile-time option, so a build must be configured with the flag to include it, and that FFmpeg prints a confident number even when the comparison is invalid - wrong input order, mismatched resolution, or misaligned frames - so the discipline matters more than the command.
