Adaptive Bitrate in the CDN and ISP
Moving up the distribution chain into the ISPs and the content delivery networks (which are topics covered in depth elsewhere in this book) HTTP presents a simplification of the distribution paradigm, and while it introduces significant latency - perhaps two or three GoP lengths (typically 8 to 12 seconds) - and while HTTP traffic itself is bursty, and cannot be managed in the same way that the superior live streaming protocols can, its very simplicity has left HTTP as the de facto way to transport streams. Incidentally RTMP now, only a few years after adaptive bitrate became commercially available, only dominates where low latency to the largest media player “reach” is the key performance indicator (KPI) for a video stream - such as for sports-betting video to web applications.
Internet Radio and HTTP
Interestingly the success of HTTP takes us back to one of the early streaming methods: HTTP progressive download. HTTP progressive download was not originally considered to be a live streaming protocol by many web- casters. This is arguably no longer the case. Referring back to the mp3 streaming example at the start of this chapter, and seeing HTTP-based adaptive bitrate streaming come to dominate today's modern delivery strategies, it is useful to highlight that the HTTP transport is not limited to streaming adaptive bitrate “chunked” or “fragmented” formats - HTTP is now widely accepted, and with that the older Shoutcast and Icecast protocols used for Internet radio streaming have seen a strong resurgence in the past few years.
These are important formats - many times as much mp3 and aac (described in Section 2.5) encoded music and radio is streamed by HTTP progressive download to many more different technologies and devices than any form of IP streaming video - not least because the 256 kbps Internet still exhibits significantly wider reach than the 10Mbps Internet!
Streaming radio does not make up such significant volumes of bandwidth and traffic online as streaming video, but the audience sizes can be staggering. A single video server may break sweat when it is serving a thousand clients - and even the best server clusters may manage only ten thousand before they need to offload to a distributed CDN.
A basic Icecast server on a domestic PC can comfortably serve 20,000 streams given suitable network interface cards and connectivity. It is important not to dismiss these technologies!