I’ve recently been watching a lot of commercial TV as I travel about the country, and I’ve been struck by one consistent issue: the low overall viewer experience in ad breaks (particularly the local commercials). Commercial stations rely on ad breaks for their revenues, but I constantly see breaks where ads are cut off, show poor video quality (a kind of “pulsing” in the video), have clear field reversal/cadence issues very noticeable on graphics, or run out of time and crash back into the long form program. This is not a geographic issue – it exists across the US – so it struck me that there must be some common problem or set of problems that result in these artifacts.
Broadly speaking, the issues can be broken down into two categories: field/frame cadence problems and timing errors. Let’s look at each of these categories to try to understand the base causes, and possible solutions.
The first issue is, in theory at least, the easiest to resolve. It is not unusual for files to be delivered to the MVPD marked as PsF, when in fact they are progressive, or even interlaced. Even if correctly marked as interlaced, they may be marked with the wrong field dominance. Another class of problems which is very common – especially with locally sourced spots – is that the original material was shot and edited @ 24fps, but the final version was rendered at 29.97fps through a less-than-pristine 3:2 pulldown process, resulting in “dirty” frames. These issues can be corrected relatively easily, but generally require highly specialized equipment and a skilled operator to do so, as it usually requires some human analysis to detect the initial cadence used (and it is not unusual for the cadence to change during a segment!). In reality, the need for human interaction means that routine correction (or correction across a library of spots) is not economically feasible. What is needed is an automated process (a.k.a. a “washing machine”) that can normalize all spots to a single, quality optimized mezzanine cadence. This capability becomes even more important as companies seek to distribute their content through newer digital distribution networks, where the distributor requires that the material be delivered in the frame rate in which it was shot, and will reject files that have incorrect cadence!
Retiming Ad Content
The second issue is more complicated to resolve but has a much more obvious cause: ad content is commonly inserted into 15, 30 or occasionally 60 second slots. But the ad content is almost never exactly 225, 450 or 900 frames long. I polled a number of colleagues in the MVPD sector, and the consensus is that a ½ to 1 second error in actual content length is the norm! The obvious solution is to insist that the content provider produce segments that are the right length, but in practice this proves to be almost impossible to do. Having content that fits exactly into an ad avail is important for normal distribution but is absolutely mandatory in targeted advertising/dynamic ad insertion scenarios. These models simply do not work if the targeted content is not exactly the same length as the slot reserved for it. So how do you correct an ad that is not the right length? The issue of content retiming exists in long form material too, but it is much more difficult with an ad as you have far less media with which to work. One common solution is to decode the original material and put it into an NLE, so that a human operator can “tighten it up”. Clearly, this model doesn’t scale, and is expensive to implement. A second choice is to use a program which will analyze the IPB cadence of the compressed source and drop or repeat some “B” frames until the material is the correct duration. This, unfortunately, can introduce some fairly significant artifacts on fast moving elements in the image – particularly graphics. A third solution is to apply a sophisticated time compression algorithm which uses adaptive interpolation to achieve the desired result. This technique is well understood, and there are several retiming products on the market, but remember: you only have so many original frames to interpolate from when talking about adverts, so the re-timer must have modes specifically designed for short form material.
As you can see, there are solutions to the root causes of many of the artifacts we can see in short form material, but the key to successful deployment of a solution has to be that it can be automated, for that is the only way to grow the solution to scale.
-Paul Turner, turnerconsulting.tv
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