Record full sessions and you'll pile up several GB an hour, when all you really want to watch are a few 10-second moments buried inside. And rewatching the long original later to find and cut those segments is no small task either. The OBS "Replay Buffer," commonly called instant replay, solves this problem from the opposite direction. Instead of saving everything and cutting later, it pulls out only "that moment just now" at the moment it happens. This article covers how the replay buffer works, the OBS setup steps, the encoding load, and this approach's clear limitation and its alternative.
What Is the Replay Buffer? How Holding the Last N Seconds in Memory Works
The replay buffer continuously holds just the "last N seconds" of footage in your computer's memory (RAM). Set it to 30 seconds, for example, and OBS always keeps the last 30 seconds of video in memory while continually discarding anything older. Think of it as a "circular buffer" that runs entirely in memory and never writes a file to disk.
Then, when a great moment happens and you hit the hotkey, the last N seconds being held in memory at that instant are immediately saved as a single video file. Unlike normal recording, which captures from "after" you press record, the key point is that you can reach back and rescue a moment that already passed. It's the same concept as a console's instant replay or your graphics card overlay's "instant replay."
Setting Up the OBS Replay Buffer, Step by Step
The replay buffer is built into OBS, so no extra install is needed. Just turn it on in the following order.
Step 1: Enable the Replay Buffer in Output Settings
Go to Settings, then Output. If your output mode at the top is "Simple," you'll see the "Enable Replay Buffer" checkbox right there; if it's "Advanced," a separate "Replay Buffer" tab appears. Checking this box reveals a field to enter the maximum replay time (in seconds).
Step 2: Set the Maximum Time to 20 to 30 Seconds
We recommend a maximum replay time of 20 to 30 seconds. That's plenty to capture a kill, a teamfight, or one big play, and setting it longer just eats up that much more memory. Since you have to keep this much footage in memory at all times, cranking it up to 60 or 120 seconds balloons your RAM usage. If you need some buffer on either side, 30 seconds is safer than 20.
Step 3: Assign a Save Hotkey
Go to Settings, then Hotkeys, and assign an easy-to-reach key to "Save Replay Buffer." A key that doesn't clash with your game controls, like F9 or a Ctrl combination, works well. This is the exact button you'll press at the critical moment. Make sure the key registers inside the game too, and check that it doesn't conflict with other hotkeys.
Step 4: Hit "Start Replay Buffer" to Stand By
Once you're set up, a "Start Replay Buffer" button appears in the control panel on the right of the OBS main screen. You have to press this button before you play for it to actually begin stacking the last N seconds in memory. If you don't press it, there's nothing to save no matter how many times you hit the hotkey. When the game ends, hit "Stop Replay Buffer."
Encoding Load: Lighter Than Full Recording, but Not Free
The replay buffer still encodes the screen in real time and stacks it in memory, so the encoding load itself is similar to normal recording. What eases the burden is that it isn't constantly writing to disk and the saved length is only N seconds. Here too, the key is the encoder.
Under Settings, then Output, set the encoder to "NVIDIA NVENC H.264" instead of software (x264), and the encoding load shifts to a dedicated GPU chip, sharply reducing frame loss in your game. Leave it on x264 and the CPU handles your game and encoding at once, which can easily cause noticeable lag in framerate-sensitive games like Valorant or Overwatch. Pushing resolution and bitrate too high raises both memory usage and load together, so we recommend starting around 720p/30fps.
- Encoder: NVIDIA NVENC H.264 instead of software (x264), to shift the CPU burden to the GPU
- Maximum replay time: 20 to 30 seconds (longer means more memory used)
- Resolution and framerate: start at 720p/30fps if it feels heavy, 1080p/60fps if you have headroom
- Auto-start replay buffer: turn it on to skip pressing "Start"
The Replay Buffer's Limit: In the End, a Human Has to Press the Button
The replay buffer is clearly a clever feature, but it has one fundamental limitation: it can't "detect" highlight moments. It just holds the last N seconds; OBS has no idea whether that's a pentakill or an ordinary stroll. So in the end, right after a critical moment passes, the user has to press the hotkey themselves.
The problem is that the more genuinely amazing the moment, the more your hands are tied up with game controls. Hitting that save hotkey during the 3 seconds a teamfight erupts in League of Legends, or the instant you wipe the team with an ultimate in Overwatch, is no easy thing. Forgetting in the heat of the moment, or pressing it too late so the start gets cut off, is common. "There's no automatic detection" is the replay buffer's single biggest weakness.
What If You Didn't Have to Press a Button? DOR's Automatic Detection
If "I forget to press it" is your core problem, the answer is an approach where you never have to press it in the first place. Like the replay buffer, DOR holds the recent segment, but instead of a hotkey, it automatically detects in-game kills and highlights and saves those moments as clips. You don't have to take your hands off the game at the critical moment.
Install it and it kicks in automatically the moment you launch a supported game like Valorant, League of Legends, or Overwatch, and when you quit, the highlights are already gathered into clips. The three steps you have to do yourself in OBS, "start the replay buffer, memorize the hotkey, press it at the critical moment," disappear entirely. NVENC hardware encoding is the default, so the load is light, and it's free with no watermark.
To sum up, if you want to choose exactly which moments to save and you'll also handle streaming and editing, the OBS replay buffer is a powerful free tool. But if your real problem is "I don't want to miss the good moments, but I keep forgetting to press the button every time," then DOR, which removes that burden with automatic detection, takes the least effort. Check out automatic clip examples on the pages for the games you play most: Valorant, League of Legends, Overwatch.
