The Ultimate Video Recording, Encoding and Streaming Guide

Buffer recording and AVIDemux

Replay Buffer

*** Currently not completely implemented. Will update when new version comes out. Currently only available in simple mode lossy. Very sad face.
*** This update has been long overdue. OBS is now version 23 and has supported buffer recording for a while. Tutorial coming soon.

Buffer recording is where you don’t record EVERYTHING that happens, but rather just certain parts. Like a highlight reel without the editing. It’s where you have OBS running with a buffer, for this example it will be 30 seconds, and if something happens that you want to save, you can save the last 30 seconds to a file.

The advantage of this is that you can play for 6 hours straight and only save 2 or 3 short blocks of video which you know are good plays. Lossless 1080p @ 30 FPS will run around 10MiB/sec so 6 hours would require over 200GB on your HDD. Then you have to watch the video and find the good bits and edit them out. This way, you know you have your good bits already prepared and lined up in neat little files. You can merge them together then encode it as one large highlight reel. What I do is I encode them FIRST, so that I have encoded copies that only take up 3GiB per hour instead of 36GiB per hour. Then I check the encoded copies to make sure they worked and look fantastic, and I delete the lossless originals and merge the new files into highlight reels. On the Unreal Aussies YouTube page there’s plenty of League of Legends and Dota 2 highlight reels along with some from Shootmania and The Hidden: Source.

Open up OBS and make sure you’ve setup your output-recording tab to record lossless or near to it. See section 8 of this tutorial for more information. Then head to the settings Hotkeys section.
Start Replay Buffer -> This button you push to begin the buffer. It will buffer up to the number of seconds you have listed under “Replay Buffer length” in the Broadcast Settings screen.
Start Recording -> Push this button to start a video file which begins from when you pushed START Replay Buffer, or from how many seconds ago you have setup in your buffer length.
Stop Recording -> End the recording and save the file.

Now, if you START Replay Buffer at the 1:07 mark and get to 22:51 and realise something amazing just happened, you can hit Start Recording. This will start a video file which begins at the 22:21 mark, so your amazing moment has been saved. Feel free at this point to make a witty comment or continue recording for a bit. When you’re ready, hit STOP Recording to finish the file. Now you can hit START Replay Buffer again to be prepared for your next amazing play!


Once you’ve got some footage saved up, it’s time to edit. Most people like Adobe Premier to mash video clips together and do some nice effects. I personally just take my 30 second blocks and merge them together, or if I record a tournament like the in-house Heroes of the Storm ones, I cut out the time in-between matches with AVIDemux. It simply creates one file and pastes all the clips you want together and can do so with no encoding nor converting. It just turns short files into a long one. There is no quality loss, but the end result is nowhere near as extravagant as something more professional.

One thing to note is that AVIDemux will only merge files that are encoded with EXACTLY THE SAME PARAMETERS. This means they need to have been done with the same profile and level, audio format and bitrate, CQ or VBR mode. I have my settings in Handbrake saved as defaults for different situations. Also, the “uA Intro” clip that plays at the start, I have encoded in Handbrake multiple times to match each of these settings. There’s the old way I did it with Fraps recordings, another way for highlight reels and a final way for tournaments like in-house nights (because they are so long I encode with faster settings). I open AVIDemux and add the appropriate “uA Intro” then proceed to tack on all the rest.

Get AVIDemux from here

Open it up. The easiest way to do this is to have a folder of your videos open next to the AVIDemux window. When you drag one over and drop it onto the AVIDemux window, it will open the file in the program. Drag the first file over and wait for it to process, then drag the next one and it will add them together into one big movie. You can keep adding more and more clips this way.

AVIDemux is a good tool to cut video bit for bit

Over on the left you want the Video Output AND the Audio Output to say “Copy”. This is the feature of AVIDemux that convinced me to use it. It means that the bitstreams for video and audio will be copied bit for bit, like passthrough audio in Handbrake. Not many programs can do this, Premiere can’t for example, at least not the version I own. If you just wanted to merge your highlights into a reel then you’re good to go. Just save the video as something and it will only take a few seconds depending on how fast your hard disk is.

If you want to cut bits out of the video then it’s a little trickier. The way H264 and H265 both work, is that they use an “I-Frame” as a picture, like a JPEG which requires no other frames to work. Then they use “P-Frames” which are stored as the difference between a previous frame and they’re not an image on their own. There’s also “B-Frames” which are the real magic, they can use a previous frame AND a future frame and store the middle-ground/weighted-average or however you want to think about it. P-Frames and B-Frames depend on other frames to give an image, so you can’t START a video with one of those, you need to start it with an I-Frame. You heard a lot about Keyframe Interval in the streaming section of this guide? Well I-Frames are the Keyframes.

So you need the END of a cut to be on an I-Frame. Down the bottom of AVIDemux it tells you what type of frame you are looking at. In the image above it’s a “B-FRM” and you can see it just next to the timer. Move the slider to exactly where you want the cut to start and click the red box button with an “A” in it. This is the start of your selection. Then do the same for your END marker, move the slider but hit the button with the “B” in it right next to the last one. This point needs to be an I-Frame, if not, then the video/audio “copy mode” we want can create errors. To end a cut at a point other than an I-Frame means the whole video will need to be encoded lossy again, losing quality. This may be what turns you off AVIDemux because if you’re going to do a whole recode, then why not use Premiere with its larger number of features? Well for me, I manage just fine with AVIDemux and setting the END point for a cut to an I-Frame usually only means a couple of seconds early. For my purposes this suits and I recommend it.

To find an I-Frame just use the blue circle buttons with the double arrows in them, like the fast-forward or rewind buttons on a remote control. These will skip to the next I-Frame in that direction. Remember, you can START your cut on most frames, but it needs to END on an I-Frame. If you’ve messed it up, AVIDemux will tell you about it when you try to save the file. When you’ve got your selection, just hit the delete button on your keyboard and it will be removed. If you save while there’s a selection, it will save JUST the selection. Once you’ve deleted it, the selection disappears and you can save the result.



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