The following article is an excerpt from Chapter 4 of HTTP Live Streaming: A Practical Guide. This is the introductory section of the chapter and is meant to give you the background you need to understand how adaptive streaming works and how to do it with HLS.
In previous chapters, we’ve seen how to stream a video with HLS for both on- demand and live video. However, a single video stream at a particular bit rate isn’t going to work on all the devices that people watch video on today. Some devices are more powerful than others, screen sizes are different, some support different H.264 profiles, and so on. Connection speeds can also vary depending on how you are connected to the internet.
For example, you can watch an HD video stream on your flat screen TV at home, but you won’t get the same experience watching the same stream on a mobile device over a cellular network. Playback will stall as the device won’t be able to download the video data fast enough. In some cases, the video may not play at all because the device won’t be powerful enough to decode the video. Then there’s the wasted bandwidth. Most screens on mobile devices do not have the same resolution as a TV so all those pixels will be wasted.
The amount of bandwidth available also plays a part. Your internet provider may promise you super-fast connection speeds, but what you actually get may fluctuate at any given time. If everybody in your neighbourhood starts streaming the latest movie from Netflix or watching YouTube videos, you can be fairly certain that your connection speed will drop off. The result? More stalls and buffering.
We need a solution that allows us to deliver a video stream that’s optimal for the device the stream is being watched on, and that is where adaptive streaming comes in to play.
Here’s the plan for what we’ll cover in this chapter:
- First we’ll look at what adaptive streaming is, how it works, and why it’s useful.
- Then you’ll learn how to take a video and stream it on-demand using adaptive streaming.
We’ll be doing some video encoding in this chapter so if you come across any terms you aren’t familiar with, refer to Appendix A, An Encoding Primer.