File-based delivery - What you need to know - Audio Media International

File-based delivery - What you need to know

File-based delivery - What you need to know
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From 1 October 2014, the UK broadcast industry is facing a seismic shift in the way programmes are delivered. While audio considerations are to the fore, if you still haven’t done anything about it yet there is no need to panic, writes Will Strauss.

Unless you’ve been living under a rock for the past 12 months you’ll know something significant is about to happen to television programme delivery in the UK. In what is described as the “biggest change since the move to colour”, from 1 October broadcasters will expect external programme suppliers to submit any new post-produced shows as a digital file rather than on a tape.

According to Mark Harrison, the chair of the Digital Production Partnership (DPP), the rationale behind the move is there for all to see: “Producers are already shooting and editing their programmes digitally. But then a strange thing happens. At the moment a programme is finished it is transferred from computer file to videotape for delivery to the broadcaster. When the broadcaster receives the tape they pass it to their playout provider, who transfers the tape back into a file for distribution to the audience.”

For broadcasters this move will mean, among other things, a single industry standard, no more tape obsolescence headaches or VTR upgrades and it should make metadata ingest easier.

But how will it affect sound engineers and audio post-producers?

The Basics

Fundamentally, the change is just replacing physical items like tapes, labels, and VT reports with their zeros and ones equivalents. So, instead of a plastic tape case it’ll be an AS-11 DPP wrapper. Inside the wrapper is the programme as a digital file and the associated metadata.

Loudness is Key

The good news is that the content creation stage remains largely the same as for tape delivery. The only real difference is the new loudness measurement technique (EBU R128).

The DPP rules are fairly clear: all new programmes must be mixed to comply with R128. Programmes that have been mixed to the old PPM6 standard, including legacy or archive content, will only be accepted by prior agreement with the broadcaster.

The loudness check is likely to be the first part of the delivery process. It has been written about constantly but for the sake of clarity, R128 looks at normalising audio and is based on average loudness rather than peak level.

Producers are being advised to “tell the post-production provider whether the programme is mixed to PPM or R128”, a decision based on the version of the Technical Standards to which the production company is contracted to deliver. So, expect a call.

Surround Sound and Workflow

For audio-only post houses, the days of laying back to tape are probably numbered. The easiest way to get around this will be to deliver .wav files to an Avid (although, it is worth mentioning that working that way it won’t be easy to check the sync as you will possibly never see the mixed audio with the finished pictures).

If there is a 5.1 Surround Sound mix required, this “must be delivered as discrete audio tracks, not Dolby E encoded”, but Surround Sound programmes still need the Dolby metadata to be sent to HD television sets. This is a grey area and development is ongoing.

Programmes delivering surround sound must also carry a stereo mix meeting all requirements for stereo delivery. This should generally be an automated down-mix of the surround channels using the same downmix parameters as are held in the surround metadata. The advice here is that “in order for both the surround mix and stereo down-mix to comply with EBU R128 the down-mix should be normalised before layback”.

Quality Control Matters

QC is affected quite considerably by the move to file-based delivery with the responsibility falling entirely to the programme producer, and not the broadcaster. There is a perception that the responsibility has been changed, in fact it has always been this way.

Broadcasters will do basic checks but won’t do a full QC check so firstly a manual QC check will be required, with humming or buzzing, silence, and lip sync among the considerations.

Then an automated QC process will be possible where some technical checks – for audio clipping, audio dropout, and audio phase errors plus loudness and maximum peak – can be done by a computer.

The Output

To complete the process the post-producer will then output an MXF file containing both the audio and video encoded material, and the required metadata. The video and audio tracks must be encoded and structured according to the DPP Technical Standards as a compatible AS-11 OP1A MXF file.

For HD files, the audio must be frame interleaved with the video and carried within a BWF container as described by AS-11. All audio tracks must be encoded as PCM with a sample rate of 48kHz at a depth of 24bits/sample.

Last-minute Changes

It is highly likely that, in the early days, this delivery process will take longer than its tape equivalent. Which is fine if you allow plenty of time and nothing goes wrong. But, and here comes the biggie, if something needs to be changed or goes wrong, you cannot currently insert edits on a file.

So, if there’s a late credit change, for example, where with tape it was easy to drop in the amended shot very quickly, with file delivery, there’s no option to do this so you have to create a new full master file.

As of now, there is no consensus on how to deal with this problem other than producers will need to adhere to deadlines. The fact that they will most likely be charged by their post house for the creation of a new master may also be encouragement.

While it sounds problematic, ITV supervising editor, Emmerdale Post Production, Gary Westmoreland does have some advice: “It is really about keeping the QC process close to your edit timeline so that if you do have a failure you are not too far down the road for you to then to go back, rewind, correct the process, re-warp, and deliver from there.” 

www.digitalproductionpartnership.co.uk

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