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IPhone HTTP Video Streaming Explained
One of the more overlooked features of the new iPhone 3.0 is support for a new open standard for live video streaming over HTTP, which promises to open up standards-based video broadcasting to a wide audience while giving mobile users an optimized picture as they roam between WiFi and mobile networks.
HTTP streaming works through a very simple mechanism. Every time a seek operation is performed, the media player makes a request to the server side script with a couple of GET variables. One is the file to play and one is the start position. The server side script then starts the video from the offset given. Below is a short example. After you start the video, you can directly jump to any part in the video without having to wait until it is loaded.
Apple's HTTP Live Streaming proposed draft looks a lot like a method Microsoft began selling last year, called Smooth Streaming. The difference is that Apple's proposed IETF standard can use anybody's encoder and broadcast server, and will work with any client software designed to receive the stream. In contrast, Microsoft's Smooth Streaming is of course designed to exclusively use Microsoft Expression Encoder, Microsoft Internet Information Server with a Smooth Streaming extension, and requires Microsoft's Silverlight 2 on the client.
What's next? The obvious followup is to add support for HTTP Live Streaming in Apple TV, allowing for HD streams direct from broadcasters, facilitating the ability to only pay for channels you want to watch, skipping around the local cable monopoly while gaining access to content they don't carry. The same content would also be accessible on the iPhone, a desktop PC, or any other device with the capacity to play modern video codecs. And that's why Apple is not supporting Mozilla's efforts to use the obsolete Ogg Theora on the web, which lacks silicon support for hardware acceleration on mobiles and appliances.
Adaptive Streaming allows programmers to offer a higher quality viewing experience to a broader audience. Being able to offer HD streams all the way down to low bandwidth streams, without pauses or interruptions of the video, makes for a significantly improved consumer experience.
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