Why is 936p and 864p so common on Twitch streams?

While many streamers stick to 720p or 1080p, it’s very common to find streams in 864p or 936p, which are interesting middle terms between the two most common standards in today’s broadcasting and live streaming world: HD and FHD.

Below I’ll talk about a few reasons as to why these are good “magic” numbers for Twitch streaming. This post assumes you have some basic knowledge of streaming and different video formats. Also, understanding a bit about intra-frame compression helps a lot — if you don’t know anything about compression, Tom Scott’s got you covered!

Let’s start with bitrate

Twitch has a limit value of how much bandwidth you should use for your video content — 6000 kilobits — or 6 Megabits per second. YouTube, for example, suggests 4.5 to 9 Mb/s for 1080p60 live streaming. Variable bitrates are simply not an option.

Anyway, 6Mb/s is too little bandwidth to stream something like a videogame capture, especially fast-paced games. This is even worse if you live in a place with unstable or limited internet, which lowers this cap even more. Sure, it’s great to slap on a 1080p60 seal on your livestream to attract audience, but it gets very rough to watch when every in-game movement the you make results in a bunch of pixel blocks for the viewers. Video encoding today is amazing and the because streaming live content from your consumer-grade PC & internet is a possibility, everyone is willing to make compromises and accept that the video quality just going to be lossless.

Considering now that we have a hard limit on how much video data we can send, and we know our encoder is doing the best it can to make it look nice, we must think of ways to optimize our setup to make the best use of those 6Mb as possible.

Trying out different formats

When you get to your technical setup, the first thing you usually have to decide is what resolution and framerate you want. While many people still don’t mind watching streams at 30fps, 60fps is always preferrable. Same goes for 720p and 1080p.

But your hardware may not be enough to handle the “best” combination — which is ideally 1080p60. But as we know, it’s too much information for just 6Mb. So those values need to be tweaked. This is about time where our magic resolutions 864p and 936p come in.

Let’s compare common resolutions

Different resolutions just means more pixels. While you can quickly do the math by multiplying the width and height of your resolution to get a pixel count, I think it’s best to have a chart so we can visualize exactly how many more pixels there are in total on these different resolutions:

As you can see, the change from 720p to 1080p is huge, with a pixel count of more than 2x. While in most contexts this wouldn’t matter because you could be willing to accept the performance consequences to achieve better quality — we have to remind ourselves again of the bitrate limitations and also think of how are people watching your 1080p stream. In fact, let’s imagine how that goes — using myself as an example:

I have a 1080p monitor… but I’m on Twitch, which is a very social platform. This means I’ll use theater mode and have the chat open to talk to other people and maybe even interact with the streamer. So even though I might have selected Source quality, I am already watching your content in a scaled-down version. To get more specific, by checking the video stats window, I can see that the display resolution is 1580 pixels wide.

We don’t even need to get too technical and you already see where we’re going with this… There are almost zero cases where I open up a Twitch stream only to have it full-screen and completely ignore the social part of the platform. Of course, that’s just me — other people may do this. But as a streamer, part of the fun is interacting with your viewers, so the ones that interact with you the most don’t watch it fullscreen.

Bottom-line is, we need to make the best out of those 6Mb/s. If you’re a professional broadcasting an event, you will always use 1080p60 — however, if you’re just streaming videogames in 1080p to your followers, you switch to these resolutions for:

• Performance gains due to 25–30% reduction in pixel count (this might give you enough headroom to attempt 60fps instead of 30, but don’t count on it!).
• Bitrate usage is way more efficient, because you have less pixels to work with, which can result in sharper and less blocky video.
• Viewers who are interacting with you in the chat are probably already watching a scaled-down version, so there are no drawbacks. In fact, this might actually bring quality benefits to them.

As a bonus, if you’re streaming in 720p60 because your hardware can’t handle 1080p60 — remember it’s about twice as much video data to encode — you might be able to make the jump to 864p or 936p.

If you want to try it out

Just set your output resolution inside OBS’s video settings to 1536x864 or 1664x936 depending on which one you want to use.

So where did these resolutions come from?

The aspect ratio standard for video streaming services of 16:9 — which is a widescreen format (bear in mind that widescreen does not mean 16:9 exclusively, though).

Knowing this, we always want to use a 16:9 resolution. However, not all of them are ideal. You will want to use resolutions that are considered true 16:9 resolutions. You can learn about them here. In short, true 16:9 resolutions are the ones which both width and height are cleanly divisible by 8.

This is because video encoders that use the compression standard H264 — like x264 or NVENC H.264 — work on the concept of macroblocks which, using the H.264 high profile, means it can use blocks of 8x8 pixels. So when you’re using a resolution that does not cleanly divide by 8, your encoder will need to remove or fill in some parts of your video content with neighbouring pixels, which you don’t want.

Until the industry moves on to other standards like H.265 or AV1, you should take advantage of this on your livestream.

Thanks for sticking through to the end. I hope this helped you have a better understanding of these “weird” resolutions. If there are any technical mistakes in this post, let me know so it can be corrected.

Have a great day!