Latency

What is video latency?

Video latency is a measure of how long it takes between when a video stream is requested and when transfer of the video stream starts. Latency is used when you are working with a live stream. In the smallest unit of measurement, its how long it takes one frame of video to move from where it's being captured by a camera to the player you want it to appear on. Sometimes this is referred to as glass-to-glass.

When is low video latency most important?

There are some situations where latency might not matter as much. For example, if you're watching a playback of an event, latency might not be a big deal, you can wait a few moments to get started watching. But if you're having a conversation, it might become difficult to have your conversation if there's drag between video of you and the other participants reaching one another. The most common use cases where you'd want low latency are:

• Two-way communication - meetings and broadcasts where you want to speak with your audience real time.
• Betting and auctions - anything where people need to place a bid or make a bet, you're going to need everything to be as up-to-date and realtime as possible.
• Video games - you need to be able to respond to what's happening in your game real-time.

What causes latency?

When live streaming, your latency is affected by many things:

• Device - you are limited by what your device is capable of.
• Distance to travel - the further your video is from its destination, the greater the chance of latency.
• Video codec and vide size - bigger files take longer to transmit, and different codecs will handle the files at different speeds, resulting in higher or lower latency.
• Bandwidth - the higher the bandwidth the faster you can stream video, resulting in lower latency.

How is latency categorized?

You may have heard about different types of streaming described with different latency terms like standard, low and others. But how much latency occurs for each type? Here's a quick list:

• Standard broadcast latency - 5-18 seconds, TV and some VOD online have this much latency.
• Low latency - 1-5 seconds, cable TV and some VOD have this much latency.
• Ultra-low latency - Less than 1 second, when you have this much latency, you're at the start of what can be used for real-time streaming. It's suitable for two-way communication, though you will sometimes notice a pause if you're trying to do something complex, like play music together across a two-way connection.
• Real-time latency - Milliseconds, you can't tell that there's a delay in most cases. This can still be noticeable for things that require precision, again the best example would be if you're trying to do something like play music, where the timing needs to be close to perfect for everyone to be together.

Video latency and api.video

At api.video, all of our video is high quality and low latency. Our streams are typically 10-15 seconds latency.