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Xbox 360 Video Streaming revealed
While the PS3 gets hacked, Microsoft seems more and more prepared to be open about its hardware. Well, bits of it anyway...
Written by Dave Taylor, 27 January 2010
Earlier this month Microsoft launched a new Xbox Engineering Blog, and the first entry from "Visigoth" goes into details on how the Netflix video service works on the Xbox 360.
The introduction is all fairly trivial stuff about how to use the UI, but further down they start to talk about the technicalities of the video streaming technology, which is where it gets interesting for nerds like us.
Firstly, where possible they now don't use the WMV stream. WMV is the proprietary Microsoft video format, and while it's very good quality, it never took off as it's not open. Instead, they now use the VC-1 codec. Now, VC-1 started life as Microsoft proprietary format, and is widely still viewed as such by some, but in fact is the product of 15 companies' patents. It is the "official" video codec of the Xbox 360.
Secondly, and this is the cool part, they have implemented "Seamless Stream Switching". When you start playing a Netflix video, the Xbox 360 samples your bandwidth to see how much is available, that is how fast your connection is. It then selects a video stream based on that, starts to buffer the video and play.
However, bandwidth can change over time, especially over the length of a film. Some ISPs allow bandwidth bursts, so you get fast initial downloads, but if it looks like you are going to make sustained use, it drops down the maximum rate. Someone else in your house might start using your network. Contention ratios in your street might change (lots of people might start using broadband at the same time).
Previously, you were stuck on the video stream the Xbox 360 had started, so your video might stick and jump. Likewise, say for example, the 360 had dedicated a slow stream because there was something going on with the network when you started, but the connection speeds up later, you would be stuck with the low quality stream.
"Seamless Stream Switching" is a system they have implemented where the Xbox 360 keeps monitoring the bandwidth and if it sees the video buffer dropping to a dangerous level, it starts a new video stream at a lower bandwidth, buffers it and swaps you over. Likewise, it steps you up if it can. It even takes steps to ensure it isn't constantly swapping you up and down.
For those who don't spend their days wondering how video buffering is done over the internet, this is a really cool system. It means not only that the system can monitor the bandwidth and get a new stream ready, but it can also know exactly where in the video stream the playhead is and work forward, get the right ongoing stream and swap at the right time. That's really hard.
So, having read this, the obvious question is whether the Xbox 360 implements this same "Seamless Stream Switching" on its other videos, such as the games videos and even the non-Netflix video rentals in other territories. We asked Microsoft, but Major Nelson told us: "What you have read is as much detail that we can go into. Sorry."
Understandable, so it leaves us with guess work. As the official video standard of the Xbox 360 is VC-1, we'd guess that the Xbox 360 does implement "Seamless Stream Switching" when it can, which is to say where the stream allows for it. Has anyone got any proof of whether it does or not, by having seen definite stream quality changes when viewing a non-Netflix video on the Xbox 360? Let us know.
