Measuring video quality
Apr 1, 2009 12:00 PM, By Bruce Devlin and Tim Harris
Quality control is a vital part of the ingest process.
Figure 1. A generic broadcast workflow
Click to enlarge
Quality control (QC) is an important part of bringing content into broadcasters' workflows and archives. Industry-wide, broadcasters spend a large proportion of their revenue on acquiring content, but this content cannot be monetized by a broadcaster until it has successfully made it into the business's workflow. Making QC a part of the ingest and transcoding process reduces the risk of poor quality content being included in the business' content archive and consequently decreasing the value of that archive. Automated QC also lowers the cost of bringing content into the business, enabling smaller markets to be addressed profitably. When ingesting content from tape, QC allows many problems to be fixed before the operator takes the tape out of the VTR, saving time and money. (See Figure 1.)
Ingest: The business process
In the broadcast industry, ingest is the “goods-in” department of the manufacturing process. Material from a number of content providers is supplied to the business, traditionally either on tape or as a contribution feed. This material is then ingested into the business's workflow. During ingest, the business systems are updated with data about the content, and then once ingest is completed, the rest of the business process is kicked off.
Figure 2. The business process of ingest, handling tapes and files
Click to enlarge
As businesses look for ways to reduce costs, many are moving to use digital file formats instead of tapes and the Internet instead of video contribution feeds. While interchanging media files removes the conversion from tape to file, the other parts of the ingest process still need to be undertaken. These include metadata entry and conversion of the file into a format supported by the rest of the workflow. (See Figure 2.)
Defining ingest as “the business process of accepting tapes or files into the workflow” gives a common approach to the process of bringing content into the broadcaster's systems. This way the broadcaster can be sure that all of the media assets in its workflow have gone through the same carefully defined processes. If you set up your business to treat ingest and QC as a single business process at the front end of your workflow, then the move from tape to file can be managed at the operational level and will involve minimal changes to the rest of the business.
Why QC is important in any workflow
In any business, QC plays an important part in ensuring that the output meets customers' expectations. QC is often viewed as an output-side process, checking the final product. However, it should also be applied as an input process in order to save the wasted effort of processing already damaged goods and prevent “garbage in, garbage out” situations.
Early QC can significantly reduce the cost of fixing errors, as detecting and fixing problems upstream is always cheaper than letting them infiltrate into the downstream workflows. QC can be used at the boundaries of any business process to check that the process is operating correctly. At each of these points, the tests undertaken as part of the QC process will be different and should be tuned to detect the appropriate errors for that point in the workflow. If the QC process can be automated, then its reliability is improved and its cost reduced. An automated QC system can pick up on errors that are undetectable by a human operator, but that still affect the downstream workflow.
In the broadcast industry, the input QC checks to make sure that incoming material is not damaged and meets the broadcaster's specifications. Material rejected at the input is returned to the supplier for repair. QC at a broadcaster's output is used to check that the broadcaster's workflow is operating correctly. Any failures point to a process or piece of equipment that needs to be fixed.
Verification vs. measurement
In an ideal world, all content purchased would be undamaged and would meet all of the delivery specifications. The ingest process, whether tape-to-file or file-to-file, would always have a perfect input and thus always create the desired output. The world, however, is not ideal, and things do go wrong. In an ingest process for playout or for library and archive use, the important question is: “What sort of QC do I need?”
A test undertaken as part of the QC process involves measuring media parameters and then making a decision as to whether the results of that test are acceptable to the business. The test results are combined into a QC report to allow the appropriate workflow action to be undertaken. The test results must be agreed beforehand to suit individual case requirements, because while too little information prevents useful actions from taking place, huge quantities of measurement results may overwhelm the business and hinder the QC operator from deciding what path the content should take in the business's workflow.
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