the "video itself" doesn't really exist. If you're on Windows and use MPC, you can test this yourself - use WMV9 as a renderer, take a PNG screenshot, then switch to NVENC, and take a screenshot at the same timestamp. You'll notice that on most videos, the screenshots are not the same (with NVEnc introducing macroblocking in darkness, which WMV9 gradients out properly). Using the rendered video as a source of truth instead of the source material itself would be as big of a mistake as using Photoshop on a JPEG.