Streaming Latency: What Causes It?

Published on: March 9, 2021
Written by:
Johan Vounckx

Previously, we’ve explored the different definitions of latency and when it is important, in this blog we will talk about where latency gets introduced in the video chain.

This is a snippet from our "A Comprehensive Guide to Low Latency" guide which you can download here.

Where is latency introduced?

Latency is introduced at many different steps in the video distribution chain.

    1. Firstly, the encoding/transcoding takes time with a direct impact on the glass-to-glass latency. A use-case dependent trade-off will be needed between latency, quality and bitrate. Typically, quality and (smaller) bitrate will be preferred unless for applications where the glass-to-glass latency is crucial.
    2. Secondly the distribution networks between source and playback device adds to the latency, as well glass-to-glass, protocol, startup and channel change latency. CDNs allow them to benefit from dedicated networks and to reduce the overall load on the distribution network by caching as much as possible.LL Cheat Sheet_End-to-End latency
    3. Thirdly, the player buffer adds to the latency. Players use buffers to cope with network variations and to avoid stalls. A trade-off is necessarily dependent on the importance of the latency and the quality of the network. This is also true for startup latencies and channel change times. One needs to define the minimal amount of buffered video before the playback actually starts.
    4. Overall the streaming protocol has a large impact on the different types of latency, because it defines how the video is divided into packets that are transferred and it directly impacts the buffer depth. Tuned or dedicated protocols are needed to achieve ultra low latencies and startup times.

Latencies of different protocols

Different streaming technology performs differently when it comes to latency. In our next blog, we are going to explore how popular protocols fare against each other. Additionally, we are also going to discuss ‘zapping time’ as one of the most important factors in optimising your viewing experience. You can also download the complete version of this topic in our “A COMPREHENSIVE GUIDE TO LOW LATENCY” guide here.

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