The beginner’s guide to low latency streaming

A lot of us are familiar with the time delay in video data transfer.

You may have experienced it on video calls and live streams, too. For instance, that one time when you cracked a joke and burst into laughter only to realize it’s a few seconds before there’s laughter on the other side.

However, you can’t afford this type of lag or latency issue when you’re interacting with a live audience, broadcasting a town hall, or hosting a virtual event. That’s where low latency comes into the picture.

So what exactly is low latency? Do you need to reduce latency for all your live events? Let’s answer all this and more in this guide.

An introduction to low latency

Low latency is the minimal delay in video data transfer from your player to your viewers’ screens.

The reduced data transmission time makes for an excellent viewing experience and facilitates interaction. But here’s the catch: for low latency, you need to compromise with reduced video resolution or quality.

Fortunately, not every live event demands low latency.

You need it when you live stream events for real-time interaction or viewing experience. In these cases, your audience expects to see what’s going on and/or participate live as the event unfolds. So you can’t afford high latency and will have to stream in lower than 4K video resolutions.

While this is low latency streaming in a nutshell, let’s dig into the details of when and how to achieve it.

What is low latency

When translated, latency literally means ‘a delay in transfer.’

In the context of video latency, this means the delay in the time it takes from the video captured from your camera to it playing in your viewers’ players.

Hence, low latency means less time in transferring video data from point A (your streaming headquarter) to point B (your audience’s players).

Similarly, a high latency means more time in video data transfer from the live streamer to their audience.

But why do you need low latency in video streaming? You don’t need low latency for every live stream that you host. But you do need it for every interactive live stream.

The key here is how much interaction your live event demands.

So if your event involves, for example a live auction, you’ll need low latency for your stream. Why? To ensure all interactions show in real-time – not with delays as that can give some participants an unfair advantage.

Let’s look at more of these use cases next.

When do you need low latency streaming?

The more live participation your event requires, the shorter transmission time you need. This way, attendees can enjoy the experience in real-time without delay.

Here are instances when you’ll need low latency streaming:

• Two-way communication such as live chatting. This includes live events where Q&As are involved.
• Real-time viewing experience is essential such as with online video games.
• Required audience participation. For instance, in cases of online casinos, sports betting, and live auctions.  
• Real-time monitoring. For example, search and rescue missions, military-level bodycams, and child and pet monitors.
• Remote operations that require consistent connectivity between a distant operator and machinery they control. Example: endoscopy cameras.

When should you use low latency streaming

Summarizing the use cases we explored above, you need low latency streaming when you’re streaming either:

• Time-sensitive content
• Content that requires real-time audience interaction and engagement

But why not use low latency for all your video streams? After all, the lower the delay in your content reaching your viewers the better, isn’t it? Well, not exactly. Low latency does comes with drawbacks.

These drawbacks are:

• Low latency compromises video quality. The reason: high video quality slows the transmission workflow due to its high file size.
• There’s little buffered (or pre-loaded) content in line. This leaves little room for error should there be a network issue.

When you go live, a streaming service like Vimeo quickly pre-loads some content before streaming to viewers. This way, when there’s a network problem, Vimeo plays the buffered content, allowing the network-caused slowdown to catch up.

As soon as the network issue is resolved, the player downloads the highest possible video quality. All this, however, happens in the background.

Translation: viewers get an uninterrupted, high-quality playback experience unless, of course, a major network mishap occurs.

When you opt for low latency, however, there’s less playback video that the player prepares. This leaves you with minimal room for error when a network issue strikes out of the blue.

That said, high latency comes handy in certain instances. For example, the increased time lag gives producers the time to censor inappropriate content and profanity.

Similarly, in cases where you can’t compromise with video broadcast quality, increase the latency ever so slightly so you can offer a high-quality viewing experience and have some room for error correction.

How is latency measured

With the definition of low latency streaming and its use cases out of the way, let’s see how you can measure it.

Technically, low latency is measured with a unit called the round-trip time (RTT). It denotes the time it takes a data packet to travel from point A to point B and for a response to reach back the source.

Now to calculate this, an effective way is to add video timestamps and ask a teammate to watch the live stream.

Ask them to look out for an exact time stamp frame to appear on their screen. Now, subtract the timestamp’s time from the time the viewer saw the exact frame. This will give you your latency.

Alternatively, ask a teammate to watch your live stream and record a particular cue when it comes. Now take the time you performed the cue on the live stream and when your assigned viewer saw it. This will give you latency albeit not as accurately as the method above. But it’s still good enough for a rough idea.

How to reduce video latency

So your live event is dependent on offering a real-time viewing experience without time lag. Or, you’ve planned participation to grow your audience engagement. Awesome!

Now how do you achieve low latency?

The fact of the matter is that there are several factors that impact video latency. From encoder settings to the streaming protocol you’re using, several factors have a role to play.

So let’s look at these factors and how you can optimize them for reducing streaming latency while making sure your video quality doesn’t take a significant hit:

• Internet connection type. The internet connection determines your data transmission rates and speed. It’s why ethernet connections are better for live streaming than WiFi and cellular data (it’s better to have those as your backups though).

• Bandwidth. A high bandwidth (the amount of data that can be transferred at a time) means less congestion and faster internet.

• Video file size. Larger sizes take up more bandwidth in transferring from point A to point B, which increases latency and vice versa.

• Distance. This is how far away you’re from your internet source. The closer you are, the faster your video stream will transfer.

• Encoder. Select an encoder that helps you keep low latency by sending signals from your device to the receiving device in as short a time as possible. But make sure the encoder you pick is compatible with your streaming service. 
• Streaming protocol or the protocol that delivers your data packets (including video and audio) from your workstation to viewers’ screens. For achieving low latency, you’ll need to select a streaming protocol that reduces data loss while introducing less latency.

Now, let’s review the streaming protocols you can choose from:

• RTMP: RTMP is a high-quality, widely used streaming protocol that helps accomplish low latency. However, it’s slowly disappearing from most workflows and is expected to be replaced by another alternative such as SRT.

• SRT: This protocol effectively transfers high-quality video over long distances with low latency. However, since it’s relatively new, it’s still being adopted by tech including encoders. The solution? Use it in combination with another protocol.

• WebRTC: WebRTC is great for video conferencing with a bit of compromise on video quality since it focuses on speed mainly. The problem, however, is that most players aren’t compatible with it as it requires a complex set up for deployment.
• Low-latency HLS: It’s great for low latencies of up to 2 seconds. This makes it suitable for interactive live streaming. However, it’s still an emerging spec so implementation support is in the works.
  

Live stream with low latency

Low latency streaming is entirely possible with a fast internet connection, a high bandwidth, the best-fit streaming protocol available, and an optimized encoder.

What’s more, closing the distance between yourself and the internet connection and using smaller video formats help.

Go live with low latency streaming