HD-SDI Embedding

Samurai-BNCOn a recent job, I had a chance to work with the Atomos Samurai – a recorder that creates either ProRes or DNxHD files from HD-SDI video, rather than the rather more consumerist (but just as good) quality HDMI signals I usually deal with. I have, for the last few years, eschewed the extra expense of HD-SDI kit in favour of ‘That will do nicely’ HDMI, but I think I’ve found a good business case for re-thinking that.*

The job was to record the output from a vision mixed feed from an Outside Broadcast truck, filming an awards ceremony. We had, in fact, each of the 5 cameras recording to AJA KiPros, but there was a need for two copies of the finished programme to go to two separate editors (myself and Rick, as it happens, working on two entirely separate edits) as soon as the event finished – even the time spent copying from the KiPro drive to another disk would have taken too long. So we added Rick’s Samurai to the chain.

We learned a couple of interesting things in preparation for the job.

Samurai_on_location_10aThe first is ‘how to reliably power a Samurai’ – its neat little case doesn’t have a mains adaptor in it, although it will happily run for hours on Sony NP-F style batteries (you can A-B roll the batteries too, so changing one whilst it’s powered off the second battery). However, I didn’t want to have to think about checking batteries – I wanted to switch it to record, then switch it off at the end of the gig, as I had other things to worry about (cutting 5 cameras, after shooting ‘Run & Gun’ style all day).

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The Samurai (and Ninja) can be powered off a Sony ‘Dummy Battery’ supplied with Sony battery chargers and some camcorders. Plug the dummy battery in, connect it to the charger and switch to ‘Camera’ mode and behold – one mains powered Samurai.

The second point is thanks to Thomas Stäubli (OB truck owner) and Production Manager Arndt Hunschok who set up the audio in a very clever way which gave me a unique opportunity to fix the edit’s music tracks.

Unlike HDMI, HD-SDI has 8 audio tracks embedded in the signal. The sound engineer kindly split his mix into 4 stereo groups: a mixed feed, audio from the presenter microphones, audio from directional microphones pointing at the audience (but away from the PA speakers), and a clean music feed.

The practical upshot was that I was able to edit several versions of the 90 minute awards ceremony (30, 8 and 3 minute versions) without the music, then re-lay the music stings (from its clean feed, or replace with licensed alternatives for the DVD version) where appropriate, thus producing a very slick result and saving a lot of time and hair pulling (or sad compromises) in the edit suite.

Technically, the Samurai footage came straight in and ready to edit with its 8 audio tracks in frame accurate sync (of course). I was able to slice it up and do a pre-mix of the required tracks.

In the past, this has been a bit of a nightmare. This time, it was easy to take audio from the stage and play with the timings for music cues.

A short technical note: be it HDMI or HD-SDI, your picture is made up of 1s and 0s and so there’s no technical difference in the quality if fed with the same source**. However, the audio is interesting. Most of the time, shooting indie films or simple corporates, you’re not going to need lots of separated tracks. When it comes to live performances or panel debates, however, the 8 tracks of HD-SDI can significantly offset the extra cost of the technology by saving time in the edit suite. Well worth a conversation with your Techinical Director or supplier to sort out the ‘sub mixes’ (separating your audio feed to the channels) and ‘embedding’ (entwining the audio channels into the HD-SDI feed).

It’s odd that this hasn’t occurred to me before – the facility has been there, but perhaps it’s that last bit of kit – the ‘HD-SDI Audio Embedder’ available from suppliers like Black Magic Design and AJA – that’s been hiding its light under a bushel. As such, it is probably the least sexy item on one’s shopping list. Not the sort of thing that crops up for the journeyman videographer, but just the sort of thing when specifying the larger jobs with rental kit.

So, note to self: when dealing with complex audio, remember HD-SDI Audio Embedders, HD-SDI recorders.

And again, my thanks to Thomas Stäubli and Arndt Hunschok for their assistance and patience.

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* One of the main business cases for HD-SDI (and good old SDI before that) was that it uses the standard BNC connector that has been the main ‘video’ connector in the broadcast industry. The BNC connector has a rotating cuff around the plug that locks it into the socket so it doesn’t accidentally get pulled out (like XLRs). HDMI – and its horrible mutated midget bastard offspring ‘Mini-HDMI’ can work its way loose and pop out of a socket with sickening ease, thus any critical HDMI-connected kit usually has a heavily guarded ‘exclusion zone’ round it where no mortals are allowed to tread, and sometimes bits of gaffer take just to make sure – in fact there is a portion of the ‘aftermarket video extras’ industry that make brackets designed to hold such cables into cameras and recorders. And, at risk of turning a footnote into an article, SDI/HD-SDI travels over ordinary 75 Ohm Coax over long distances, unlike the multicore short lengths of overpriced HDMI cables. So, yes, HD-SDI makes sense purely from a connector point of view.

** Notwithstanding the 4:4:4:4 recorders from Convergent Design and now Sound Devices. Basically, a 1.5G HD-SDI signal carrying a 10 bit 4:2:2 output will be indistinguishable from an HDMI signal carrying a 10 bit 4:2:2 signal, and many cameras with both HDMI and HD-SDI output 4:2:2 8 bit video signals anyway. But HDMI only does 2 channel audio whereas HD-SDI does 8. Back to the story…

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