21 October 2014
The quest for “Broadcast quality”
Delivery of content over internet connections has been around for many years now. The number of different providers of such content make for a dizzying selection for end users. Some of course have their own content available (such as catch-up services e.g. BBC) while others have branched into this (e.g. Netflix, Amazon etc). For many of these services, content is king, but what about quality ?
Quality when it comes to IP delivered content is often referred to using standard broadcast terminology, such as SD, HD, 4K etc, while often not exactly matching the equivalent broadcast specification. Since different technology is often used for IP services, then direct like for like comparison doesn’t work. For example, many of the IP services use newer compression technologies when compared to Broadcast. An example of this is that in the US, MPEG2 is used to broadcast HD content over ATSC, while no IP service will use MPEG2 due to better compression standards which are available (such as H.264 / H.265).
As a result of this, quoted quality can vary from provider to provider. Often frame resolution is used (e.g. 720x486, 1280x720 etc), but the quality of a given frame also depends on the bit rate used and the overall quality on the number of frames per second etc.
While the above is the quoted quality, the real life experience is often short of this. The reason for this is due to the method of delivery. Sending video packets over the internet takes up massive amounts of bandwidth, indeed this is the largest use of internet bandwidth. In the vast majority of applications, each video stream requires its own separate connection. In order to send video from the operator to the viewer, the packets of data have to pass through many stages, which may result in bottlenecks, where the available bandwidth is reduced. Some operators try to store copies of the video as close as possible to the end users, a process which is known as edge caching. While edge caching can help to reduce some bottlenecks, in many cases the bandwidth of the viewers internet connection is actually shared between a number of houses / users. During peak times, when everyone wants to watch, the available bandwidth per user can be reduced.
Video operators way around this is to use tools such as adaptive streaming. With adaptive streaming, the video content is prepared with a number of different bit rates and split into small sections. The viewers video player can choose which bit rate is best for the current available bandwidth, so that the viewer has almost always something to watch, but the quality can vary drastically.
Due to the unpredictability of a viewers environment, and the competing factors for bandwidth, streaming quality is a viewed as a critical measure of the quality of a service. Some operators, such as Netflix, have entered into agreements with Internet Service Providers (ISP’s) to try to guarantee a level of service as they move towards higher and higher bandwidth with 4K content etc.
Recently some infrastructure providers have started promising that using their technology you can get “towards broadcast quality streaming” for their multi-screen applications. There is of course a simpler way to get broadcast quality, use broadcast television. This is the core of Tablet TV, quality television experience, no matter what your broadband connection is like.
Dr Glenn Craib
Vice President Products & Services