1 second stream latency is possible on Twitch.
My mind is officially blown. Mixer may be gone, but that doesn't mean low-latency
streaming had to go away with it. I'm EposVox, the Stream Professor, and
today we're looking at some new findings from Xaymar - the gentleman behind the
StreamFX plugin and who has taken my core VMAF testing concept and completely
enhanced and automated the workflow for video quality comparisons and so on
- which we will hear more from soon. I love having someone like Xaymar in my circle,
because he has the workflow and the time to dive into the deeper details of video encoding that
I don't always have time for, and recently he's stumbled into a discovery that's
been under our noses the entire time. Reducing latency, or lag or delay, of your
stream getting from your streaming program to Twitch has been a desire of many
streamers. The disconnect of a streamer trying to interact with chat, but on a 5 to
30 second delay can be super frustrating. Mixer, Microsoft's acquired streaming platform
and attempt at competing with Twitch utilized a different streaming protocol called FTL
- or Faster Than Light - which had near sub-second latency and was honestly a wild
experience to interact so quickly with chat to where often questions felt like
they were being answered as soon as you hit the enter key. This was
appealing to a lot of streamers. Well, good news, it turns out that
just by setting your KeyFrame Interval to a second and a half - instead of the
recommended 2 second interval - you can potentially reach 1 second latency,
as well! But it's not perfect. What even is a "Keyframe
interval"? Glad you asked! No.. no, Ryan in the back, I know
YOU didn't specifically ask... that's not the point- You know what?
Just get out of my classroom. Just go. Keyframes in video encoding are actually called
"i-frames" or "intra-frames" - that is to say, a single frame in the video that contains the
complete image. So if you had a completely raw, uncompressed video feed and took a screenshot
from it - like in JPG or BMP image formats. This contains all of the information for the frame
at that exact moment in time. These can help, or hurt, video encoding algorithms as they
serve as reference points to build the rest of the frames, which typically contain only parts
of the data that have changed from that keyframe. Now, you can record completely i-frame based
videos in many cameras, or even in your video encoding settings with a keyframe interval of
1, and playing these back or scrubbing through these clips on a video editing timeline
is super smooth because there's no real interpretation to be done. It's just
an image sequence at that point. The downside is that these
are much harder to compress, since they are the entire
frame's worth of information, rather than only the changes. The more
information you have, the harder compression is. These differ from P- and B-frames, as
B-frames are "inter frames". B-frames, which you have a setting for with the
NVENC H264 encoder, save space by using the differences between the current frame and
the previous frame to determine its content. Going back to Twitch specifically, the usual
recommended setting for Keyframe Interval is 2 seconds. That means every other second, or
once every 60 frames in a 30FPS stream or every 120 frames in a 60FPS stream, there will be a
keyframe to build the rest of the frames from. This seems to be a balancing act of
both encoding performance and quality within a limited bitrate - Twitch is
notorious for their very restrictive bitrates - and decoding performance for
Twitch's side of the stream handling. The more keyframes you have, the more
information your video COULD contain, but the harder (and slower) the encoding process
will be. So if you're doing a mostly uncompressed video feed, more keyframes is better. But if
you're doing a very compressed video feed, say streaming to Twitch for example, more
is worse because they're harder to compress compared to P- and B-frames, worsening
quality and taking longer to encode. Well, Xaymar was hunting around for
encode settings that had an impact on the latency between his stream and Twitch
and found that... most settings had none. Even setting NVENC to the Low-Latency or
Zero-Latency mode - which people often foolishly recommend for this despite me saying
otherwise many times - had no impact here. The one setting that made all the difference
was the KeyFrame Interval. Setting it to 1 was not useful, as the latency was still
around 2.4 seconds for some reason, but he tried a fractional latency - something
only supported in X264 and his StreamFX plugin's NVENC encoder and BAM, about 1 seconds
of latency from his PC to Twitch. Which, combined with the processing delays on his PC and
etc. realistically ended up closer to 2 seconds. I was able to re-create this and
wanted to share my config, as it's damn impressive. Let's talk about the exact
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checkout to get up to 10% off at the link below. First and foremost you do, of
course, need to enable "Low Latency" in Twitch's Dashboard and make
sure it's enabled for your video player. Next is to go to your output settings in OBS.
This does need to be in Advanced mode. Not all streaming software will let you control this
granularly, we're focusing on OBS Studio here. Let's cover both NVENC and X264
settings to make this happen. First, if you're using NVENC you'll need to use the NVENC
encoder provided by Xaymar's StreamFX plugin, not the one that ships with OBS.
Xaymar's provides way more options, though it can be overwhelming to dig through.
Here's the settings I used and he recommends, but obviously adjust your bitrates
according to what you usually stream at. The important number here is the "Key
Frames" section, setting Interval Type to Seconds and Interval to "1.50 seconds." If you're using X264, you can't actually
manually type in a fractional keyframe interval, so set it to 1, and then go down to
the custom X264 arguments section and type in "keyint=90" if you're streaming
60fps, or "keyint=45" for 30fps. Again, it's 1.5 seconds, so
1.5 times your framerate. Bam! Using R1ch's Twitch Test and choosing
the lowest latency server to me I was able to re-create this myself on my test account,
though I did have to toggle "Low Latency" on and off in the Twitch player preview
sometimes to get it to grab the faster feed. You will have some variance on this based
on your routing from your ISP to Twitch, the usage level of the Twitch ingest server you're
using, and etc. so it won't work perfectly for everyone - but this seems to be the best way
to reduce your latency to Twitch while having no significant impact on video
quality or anything like that. Did this work for you? Comment below. Hit
the like button and subscribe for more tech education. Join us on Discord to chat about this or other streaming topics. I'm
EposVox and I'll see you next time.
