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Automated Checking & Correction Tools For Broadcast Delivery Specifications

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Back in the last millennium, when the finished product of a production company was delivered on video tape, quality control was focussed on technical parameters of the video and audio signal on tape – video levels, colour gamut, audio levels – and some tape quality checks such as drop-outs. By Joe Newcombe, Sales Manager, Telestream QC Products.

As long as the signal quality was acceptable, you could be sure that the tape would be accepted and would play in the broadcaster's decks.

Now that programmes are delivered over IP as files, quality control has been simplified in some aspects, but made much more complex in others. You no longer need to worry about tape drop-outs and analogue artefacts, but you still need to check that video levels and colour gamuts are within legal limits, and that your programme does not trigger Photo-Sensitive Epilepsy (PSE). In the audio domain, you still need to check that levels are correct, but now they should comply with EBU rec R-128, which defines average and peak loudness levels.

With files, unlike with videotape, you could create beautiful programmes with perfectly compliant video and audio signals, but if the encoding parameters and video file structure are not as defined by the broadcaster, the programme will be rejected.

In the UK and Ireland, the Digital Production Partnership (DPP), publishes a highly detailed delivery specification for all programmes and commercials. This defines precisely the video and audio signal levels, timecodes, lineup of the asset, encoding structure, and the metadata to be contained in the file. Checking that your output meets this specification would be almost impossible without smart QC tools such as Vidchecker and Vidchecker-post.

Within Vidchecker products, there are a large number of pre-defined templates for automatic checks against defined specifications. DPP for UK broadcasters, AS-10 for France, ADR-ZDF-HDF for Germany, IMF for Netflix, iTunes for Apple... and many more. Checking and proving that your product complies with the specification can be as simple as dropping the file into a folder, then waiting for the test results (typically about the same time as the duration of the programme).

Assuming the file complies, you get a pdf report which can be sent to the customer to prove that the file complies with every technical aspect of the specification. While this all seems straightforward, there are a few aspects of automated QC which can cause confusion, and which Telestream Vidchecker aims to resolve.

• Making the Results Easy to Understand
Many QC products are derived from lab tools, so they provide a huge depth of detailed information, much of which may be unnecessary. Vidchecker products focus on checking that a file complies with defined industry specifications, and presenting these results in operator-friendly formats. Alerts can even be customised to use your preferred terminology or language for the condition detected.

• Manual Review Tools
Auto-QC will often raise some marginal or ambiguous errors alerts. For example, if black frames and silence are detected in the content, this could be an intended part of the programme. Telestream offers the VAMP media player, in which QC alerts are marked on the timeline, making it simple for an operator to review the content at the marked points and edit the QC report to indicate whether or not there is, in fact, an error.

• Adapting to New Requirements
Even though Vidchecker includes test templates for all of the major delivery specifications in use today, we know that new or custom specifications can appear, and customers cannot afford to wait until product manufacturers include these in the product templates. In Vidchecker, we have a unique auto-template function which allows the user to create a new test template in just two clicks, based on a reference file.

• False Positives
A common complaint against Auto-QC is that systems produce a long list of marginal or dubious flagged errors. In some cases they may be marginal excursions outside of legal limits, but in others they might be due to the interpretation of file formats (which are not always as tightly defined as you may think).

Telestream Vidchecker provides tools to reduce these "false positive" reports which can be huge waste of time. The user can define the tolerance levels for tests such as video and audio signal levels, thus removing the very marginal failures from future reports.

• Automatic Correction
QC systems will detect genuine errors that need to be corrected. If these are errors in the lineup or the signal levels, an editor would usually prefer to take the programme back into the edit suite or audio sweetening room to make changes. Unfortunately, there isn’t always the time or budget available to allow this.

Vidchecker correction options can automatically correct the most common errors that occur, such as luma levels, colour gamut errors, lineup and timecode errors, and can even mitigate luminance levels to comply with Ofcom regulations on PSE.

Vidchecker is designed to support broadcaster and telco workflows, allowing four concurrent tasks and unlimited CPU core usage. Vidchecker-post is designed and priced to suit the workflows and budgets of post-production and production companies, allowing a single task at a time and using eight CPU cores, at a much lower price.

This article is also available to read at BFV online as part of this issue's Test & Measurement feature here, page 44.


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