HTTP Streaming: What You Need to Know
Hybrid solutions
Besides the progress of streaming and progressive download features over the past few years, which brings basic functionality between the two types of delivery within a very narrow range, additional hybrid solutions have been proposed.
Microsoft Smooth Streaming Microsoft’s Smooth Streaming combines HTTP delivery and adaptive bitrate technology. Three major needs have pushed these hybrid solutions forward: efficiency, scalability, and ubiquity.
On the efficiency front, there are numerous past solutions that wrap RTSP streaming video traffic into HTTP packets.
"RTSP streaming [via] HTTP packets … appear identical to standard web traffic and therefore are permitted through most firewalls," Apple stated in a document about the difference between RTSP and HTTP streaming. "This involves [an] extra layer of overhead however, resulting in a greater demand for bandwidth."
Flash HTTP streaming is another example. Up until Adobe’s announcement of its HTTP/adaptive bitrate solution (which had not launched as of the time of this writing) anyone referring to Flash as HTTP streaming actually meant HTTP tunneling.
The reasoning for this misnomer is fairly simple: The Flash server that used the real-time media protocol (RTMP) was designed to be delivered on TCP rather than the UDP delivery of the more traditional RTSP steaming protocol. Given RTMP’s ability to deliver via TCP, Adobe integrated RTMP tunneling via HTTP for both live and on-demand content. This appears equivalent to HTTP streaming. But the tunneling, in fact, causes a bit of an extra delay that might not be acceptable in all situations.
Based on the efficiency limitations, both Adobe and Apple have chosen to move toward true HTTP streaming solutions. Apple debuted HTTP streaming, sans adaptive bitrate streaming, for the iPhone when the phone launched in 2007.
Some content delivery network (CDN) vendors refer to their HTTP video file downloads or HTTP progressive downloads by the term HTTP streaming.
In terms of scalability, the need to consistently scale content to television-level audiences on any given day, without requiring weeks of preplanning for every web television event, has led to discussions of solutions that will allow streaming to scale to these levels. At the end of the article, I’ll discuss multicasting and peer-to-peer delivery as long-term solutions. The short-term solution is a combination of the benefits of streaming and progressive downloading.
Finally, on the ubiquity front, as previously mentioned, much RTP/RTSP traffic is blocked by a high number of firewalls, making it difficult to deliver streams reliably. Even instant messaging audio and video conferencing capabilities, such as those used by Skype or iChat, rely on RTSP. Even beyond the typical firewall, however, is the ability to handle content delivery between different network types. Apple chose to go to HTTP streaming for the iPhone primarily based on the concept that RTSP video streaming on the iPhone would be difficult for a device that routinely moves between Global System for Mobile (GSM) and Wi-Fi networks.
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