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User created PC mod for Street Fighter 5's netcode attempts to fix desync bug and is causing a lot of discussion in the community

Posted by Dakota 'DarkHorse' Hills • January 9, 2020 at 12:50 p.m. PST • Comments: 72

Disclaimer: Any mods or alterations to Street Fighter 5 can potentially be risky to your CFN account and / or PC. Mods are always at your own risk. Some people swear by this netcode fix, while others say it caused them or others additional problems. We recommend that if you decide to proceed, do so with caution.

Street Fighter 5's netcode issues have been heavily discussed in the years since the game's release, and allegedly one such related bug in the fighting game's code has been singled out by a modder looking to address said issue.

A Reddit user going by the name of Altimor released last night what they describe as a netcode fix for Street Fighter 5 which attempts to rectify a desync issue with players' game clocks on PC that can cause unneeded lag. It by no means seems to be a perfect solution, however, and introduces new problems to the mix.

Altimor claims that online Street Fighter 5 matches can desync from each other if one player's game runs slower / lags behind their opponent. The bug in question seems to indicate that the game on its own does not properly update its game state to bring both parties back in line and thus causing some bad rollbacks throughout the round.

This new mod reportedly changes the code so the player with the fan-made workaround doesn't experience more one-sided rollback issues than their opponent which they describe in more detail on the Reddit thread.

Altimor's Explanation for the Netcode Mod

SF5 has a bug where one player's game can lag behind the other's online. This can cause artificial lag and one sided rollback for the other player.

When the players' "clocks" are synced, if there is e.g. a 4 frame packet round trip time between them, each player should be 2 frames ahead of the time of the last received input from their opponent, and experience 2 frame rollbacks.

If one player lags behind, the other player will receive inputs from farther "in the past" (up to 15 frames!) than they should, causing unnecessarily big rollbacks and artificial lag, while the player that's behind may even be receiving inputs that appear to be "in the future" to their game and never experience rollbacks at all.

This fix ensures your "clock" never gets more than half of your packet round trip time ahead of your opponent's so that you never experience more rollback than them.

What this change does in practice it seems is temporarily slow down the modded user's game in order to sync back up with an opponent instead of skipping / jumping around as the game does now.

Claims like these of course caught the eye of the community who were eager to try out anything that could potentially help their online matchmaking experience which has led to reports by players of much improved matches but also some new problems.

Fighting game commentator UltraDavid streamed Street Fighter 5 last night for over an hour using the unofficial patch and reported that while it's not perfect, it still provided a "gigantic improvement" for him even when playing someone in Saudi Arabia from California.


Click images for full versions

That doesn't tell the whole story of what this mod can do, however.

Other players tested how matches perform when paired with modded users versus un-modded users with multiple reporting that this supposed netcode fix can essentially make the game unplayable for the person who is not using it by dumping the one-sided rollbacks onto them instead.

This is a massive potential problem for PlayStation 4 players who have no choice in the matter, and can easily create an uneven playing field for those on PC with the changed code — a flaw that the creator even acknowledges and claims to want to fix in the future.

Considering this user-made patch has been out in the wild for less than one day, there will need to be much more testing required to see just how much of this is a legitimate potential benefit and how much could be part of the placebo effect or detriment to the wider playerbase.

Capcom itself has been silent on the development thus far though they don't seem to be banning players who are using the mod online. That is something which could change at any time, however, so you may still be putting your CFN account at risk for running it.

Street Fighter 5 does offer the option to blacklist laggy opponents after online matches so you'll never encounter them again in ranked search — which everyone should keep in mind for regular play or if players do begin abusing the netcode mod.

Worries about the upcoming online tournament mode in SF5 have also been expressed in regards to this mod though that hopefully won't turn into an issue since the feature does offer an objection functionality that will disqualify anyone overtly causing lag or poor connections.

Other programmers in the FGC like Loïc "WydD" Petit seem to be impressed by the work, but even he warns against using the fix in general matchmaking for the issues it can cause when paired with an unpatched game.

This development does raise some new questions about Street Fighter 5's systems and implementations, so hopefully this community-wide response can at the very least get Capcom to open up more about what is and isn't going on with their online infrastructure.

If you want to see what the netcode mod looks like when all seems to go well and both players have it installed, Arlieth in California uploaded a clip playing against Keoma in Brazil with comparisons of what their matches looked like with and without the patch active.


Click images for full versions

It's not time to jump for joy yet, but perhaps more testing and community awareness could really make an impact on the game for everybody, for the better. Again, using this or any PC mod can have unintended side effects / consequences, so know what you're getting yourself into before diving in if you so choose.

Sent in by meltsy, Saldejums, JTCircus, Moogletee, DarkSamus, loveshocker, Mike_Z, chrobaciky, KnyghtFall, Cruiser, pip, RebornOdin, PlasmaWaffle, RougeMephilesClone, Montsegur and anonymous users.

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