Live streaming latency

30/11/2019

Stream latency is the delay between your camera capturing an event and the event being displayed to viewers. When setting up your live stream, think about how the level of latency may affect your viewers. 

If you live chat with viewers, a lower latency is best to respond to viewer comments and questions. Note that with lower latency, your viewers may experience more playback buffering. 

If you don't interact with your audience, a lower latency is not as important.

Why is there a trade-off between latency and quality?

The lower the latency, the less read-ahead buffer the video player will have. The amount of read-ahead buffer is important because it is the main source of stream latency. With a lower latency, viewers are more likely to feel the bumps in the overall live streaming network from the encoder to the player.
Network congestion and other factors may also cause live streaming issues, which can delay your stream. Delays can happen even when you have a great network that is able to sustain your average streaming bitrate.
Generally, your viewers' player can absorb these changes in internet connection speed by keeping an amount of live stream data in reserve (called Buffer Health in Stats for Nerds). 

How to change live stream latency

In Events:
  1. Go to youtube.com/my_live_events.
  2. Click or tap +New live stream / Edit.
  3. Select Advanced Settings.
  4. Select Stream Optimizations.
  5. Save your changes.

In Stream now: 

  1. Go to youtube.com/live_dashboard.
  2. Select Stream Options.
  3. Select Stream Optimizations.

​Note that mobile always optimizes for ultra low-latency.

There are 3 options for live stream latency:

Normal latency

Best for: reduced viewer playback buffering.
Choose "Normal latency" if you don't plan to interact with your audience. This is the highest quality setting for viewers since it has the lowest amount of viewer buffering.
All resolutions and live features are supported at Normal latency.

Low latency

Best for: near real-time interactivity
Choose this option if you want low latency with minimal viewer buffering. This setting is a good balance between the other two options. 
This setting does not support 4k resolution.

Ultra-low latency

Best for: highly interactive live streams with real-time engagement
Choose this option if you want to maximize engagement with your audience and don't mind increasing the chances that your viewers may buffer more.
This setting does not support 1440p and 4k resolutions.
Note: live ingestion issues on your network will affect viewers more in this setting. Consider decreasing your ingestion bitrate to ensure that your network can sustain the stream.

* Nguồn: Youtube