When it comes to video streaming, protocols are a set of standards that determine how data is packaged and delivered. What protocol you use is determined in part by the devices to which you want to stream. ABR streaming works with all the most popular protocols.
Apple developed HTTP Live Streaming (HLS), and it used to only work with Apple devices. Now the protocol is device agnostic, making it a versatile choice for both Live and OTT streaming. You need the H.264 or H.265 encoding formats to use this protocol.
Sometimes referred to as DASH, Moving Pictures Expert Click Dynamic Adaptive Streaming over HTTP (MPEG-DASH) was the first adaptive bitrate streaming protocol to become an international standard. MPEG-DASH does not require any specific encoding formats. However, you cannot use it natively with Apple devices.
Originally designed to work with the now-discontinued Adobe Flash, HTTP Dynamic Streaming (HDS) can be set up for on-demand or live streaming. Like MPEG-DASH, it doesn’t work with Apple devices.
ABR can work with Web Real-Time Communication (WebRTC) in several ways. This can be done on the server side, where the server is creating the various versions of the video data, or on the client side (a.k.a. simulcasting), where the client machine performs this task. WebRTC is well known for its ultra-low-latency streaming. However, without the help of a streaming service, it may not scale well to larger audiences. It, too, is not supported on iOS.
All the above protocols work with Hypertext Transfer Protocols (HTTP)-based streaming as opposed to Real-Time Messaging Protocol (RTMP). ABR was created for HTTP-based streaming. As such, it is much easier to include ABR in your HTTP-based streaming solution than in your RTMP-based one. It is technically possible to make the latter work but not recommended.