I couldn't easily pull up any screenshots, but I've been a video encoder for some years and I can tell you that psy-rd (the x264 option to add film grain) does

I couldn't easily pull up any screenshots, but I've been a video encoder for some years and I can tell you that psy-rd (the x264 option to add film grain) does wonders in terms of grain fidelity. The problem with matching the grain perfectly without the randomization is that it drives the bitrate crazy. A movie with 99% fidelity grain and 0 psy-rd will have a bitrate of 30mbps+. If you use psy-rd though, you can get to 99% fidely grain at closer to 20mbps. The two screenshots will be visually indistinguishable, even when you are rapidly switching between the source and encode, even though you know that the grain is being randomly generated you can't tell. If I get a chance later today I'll drop some comparison screenshots for a film encode that used a lot of psy-rd, I think the results will surprise you.