Broadcast quality control in the IPTV world

Quality control is becoming more important than ever in television (writes Steve Nunney, Managing Director of Hamlet, a UK provider of measurement and monitoring equipment to the television broadcast industry worldwide). Audiences care about technical quality, and notice failures. They are watching on larger screens than before, and these magnify any failings. Ideally, they would like HD content on their HD-ready screens.

This is a particular problem for IPTV operators, for a number of reasons. First, there is the pure technical reason that bandwidth is precious, and the temptation to increase compression ratios to save bitrate is strong. But the lower the bitrate the more artefacts will be visible.

Second, in general viewers will have to be tempted to take an IPTV service, and will already have experience of the sort of quality available on terrestrial, cable and satellite services. If IPTV offers a noticeably worse quality of service they are likely to reject it immediately, leading to high levels of churn.

Third, because they are switchers, they are more likely to complain. So while consistently limited quality will lead to churn, short-term quality problems will lead to heavy loads on the call centre. In turn this will be unlikely to be able either to help with the issues or give a convincing answer, which again leads to customer dissatisfaction and ultimately to the loss of a subscription.

So it is clearly important for IPTV operators to keep track of the technical quality of the output. What does this mean in practice?


The impact of compression

There are, in effect, two sorts of services within IPTV: the pass-through of linear channels, and video on demand and other interactive content. Each need a slightly different quality regime.

One could argue that the IPTV service is simply the carrier for channels produced by broadcasters elsewhere, and indeed it is reasonable to expect that professional broadcast playout centres will deliver a seamless, technically accurate feed. The problem comes with compression and the fact that, while bandwidth is a cost for all delivery platforms, for IPTV the sheer practicalities of the infrastructure mean that you have to keep bitrates down.

While we are still using ADSL, the lower the bitrate the further it will reach from the DSlam, and so the more subscribers will be able to receive a stable service. And when VDSL or fibre to the home become a reality, the pressure will be for more services not for a bigger bit budget for the existing limited offering.

The compression engine for each channel may be located at the broadcaster or at your premises, or you may get a higher bitrate general feed from the broadcaster which you transcode to your output standard. Whatever the route, it is important to know what that compression is doing to the signal. You have to monitor the impact of the compression, and use that to build up a clear understanding of what you can and cannot do; what your subscribers will and will not tolerate.

So you should be comparing the signal before and after your delivery compression. Which sounds reasonable, until you consider that you may have tens or hundreds of services in your offering. Watching each one for artefacts is not a practical proposition.

The solution is an automated quality control monitoring system. This usually comes in the form of specialised software which runs on a standard PC, and is capable of checking a whole range of video, audio and metadata parameters in real time. As it finds errors – excursions outside the limits you have set as acceptable for your subscribers – it will write them to a log. Serious errors can be acted on immediately. Complaints to the call centre can be reconciled against the log to determine whether there was a real quality of service issue, and you can use this knowledge to fine tune your operating practices.

If you are handling your own compression or transcoding, you can compare before and after to see precisely what impact it is having on the signal. Again, this is vital information to set the balance between perceived quality and bit budget. It also enables you to track when the fault is with the broadcaster, to see if their feed is maintained consistently to the standard you expect.

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