To be able to stream video –that is, for a video to play immediately when a button is pressed on a website–, a software program that is exclusively dedicated to that purpose is needed. That means you cannot use the same, traditional web server that delivers all forms of web content, including text, images, or other files. You need a streaming server.

One option is choosing progressive download, which is video delivered by an HTTP web server instead of a streaming server. 

Its main feature is that video is stored on the viewer’s hard drive, which guarantees a smooth view. Some of the most popular streaming services offer this option, understanding viewers move around and are not always connected to a WiFi network.

In contrast, adaptive streaming encodes multiple streams (live or on-demand) and switches them depending on the line conditions. For example, a high-quality stream when there’s a good connection, and a pixelated, low-quality video when the connection is unstable. But the video is delivered, nonetheless, and viewers are not left empty-handed. 

Depending on the viewers’ expectations and the available tech, the choice between adaptive streaming and progressive downloads can be made.