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8 Frames in 16ms: Rollback Networking in Mortal Kombat and Injustice 2

31 videos recommended on HN
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4 HN users recommended this talk5 months2020–2025 score 5
Years with an HN recommendation, 2007–2026

HN treats it as the definitive practical talk on rollback networking in a shipped AAA fighting game.

A 2018 GDC talk by NetherRealm's Michael Stallone on the engine changes, optimizations and tooling needed to roll back and re-simulate up to 8 frames in 16 ms in Mortal Kombat and Injustice 2. It is a deep dive into deterministic rollback netcode.

“For an in-depth explanation, see this excellent GDC talk on its implementation in Mortal Kombat and Injustice 2” (HN, 2023)

5 recommendations · 1 citations · Talks · advanced

6 Hacker News comments

From the HN archive; up to 20 kept per video, favoring different commenters. Recommendations first.

@syspec Jul 2020 Recommends
on HN thread Dolphin Progress May and June 2020
Do you have a link to any blog posts, i would love to read about it. I tried to look on [link] , but development appears to be closed source? I'm just an outside observer, but i love the topic. For others like myself, this is a great GDC video to watch on the topic > 8 Frames in 16ms: Rollback Networking in Mortal Kombat and Injustice 2 [this video]
Great GDC talk on rollback networking.
@syspec Feb 2021 Recommends
on HN thread How fighting games use delay-based and rollback netcode (2019)
Here's another great video on the subject: 8 Frames in 16ms: Rollback Networking in Mortal Kombat and Injustice 2 [this video] One of my favorite topics, partially because there's not that much literature on the subject but it's so important
Another great video on rollback networking.
@dilap Oct 2021 Recommends
on HN thread 1500 Archers on a 28.8: Network Programming in Age of Empires and Beyond (2001)
I guess it depends on how high a level you're looking at it from. Both lockstep and rollback are variants of the general approach of "shared deterministic simulation" where you're mostly just sending inputs. ("Mostly" 'cuz on reconnect or desync or whatever you'll probably want to send full state.) I really enjoyed this GDC talk on rollback networking: [this video] (From 2019.)
Enjoyed GDC talk on rollback networking.
@Oberdiah Oct 2023 Recommends
on HN thread Ready Player Two – What the Multiplayer Web Can Learn from Video Games
Specifically "Deterministic Rollback", as the clients don't wait for the server's response before displaying the change locally. For an in-depth explanation, see this excellent GDC talk on its implementation in Mortal Kombat and Injustice 2: [this video]
In-depth explanation of deterministic rollback in Mortal Kombat.
@c4wrd Mar 2025 Recommends
on HN thread Activision Cut Call of Duty's Build Time by 50%
Read more
For those who aren't in the video game development field and like technical content, I cannot recommend watching GDC's content enough (even better, attending!). Although this blog post isn't as detailed as I've seen them do in the past, I appreciate that game developers have the opportunity to share their wins like this externally. If you enjoy watching technical content and video games, the following videos are greatly entertaining deep dives into ludicrously technically complicated bugs or performance optimizations done to deliver the gaming experience that I myself take for granted. - I Shot You First: Networking the Gameplay of Halo: Reach: [link] - 8 Frames in 16ms: Rollback Networking in Mortal Kombat and Injustice 2: [this video] - It IS Rocket Science! The Physics of Rocket League Detailed: [link] - [link]
Entertaining technical deep dive among recommended GDC videos.

Citations, criticism and jokes

@honkycat Apr 2021 Cites it
on HN thread DreamWorld (YC W21) MMO raises all red flags
Read more
I do indie game dev as a hobby, and I have taken multiple classes on networked multiplayer, and I've also implemented VERY SIMPLE proof of concepts for multiplayer fighting games in Unreal Engine. I think what a lot of people are missing here is the context that there is STILL not a "make it multiplayer" button in game engines. They do NOT do most of the work for you for any facet of game development. Making games is still a ton of work. To name a few things that Unreal Engine does not do for you: networked movement prediction, acceptable LERPing to positions when client/host disagree, anticheat... basically it has a nice client/server model API you can use. You can annotate structs to efficiently be transmitted over the internet, and query the API to see if you are "host" or "client". There is an amazing talk on this from the Mortal Kombat creators about how long it took them to get their netcode right[0]. Now make that much harder when dealing with millions of players in one world, with mold-able terrain and an exotic networking stack. 0: [this video]
Talk on how long Mortal Kombat took to get netcode right.

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