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Comment by evan_ | Hacker News Reader

Detail from the comments, about the QR-code-like blocks that appear between sprocket holes:

> The blocks also carried software, so that the decoding equipment (such as the DA-10 and DA-20) could have their firmware automatically upgraded in the field, just by playing a newly-released film! Pretty advanced for early 1990 electronics.

I found another oblique reference to this in the manual for the Dolby DA20 sound processor, page 8-6 here, where it refers to "dynamic loading":

http://www.film-tech.com/warehouse/manuals/DOLBYDA20.pdf

however, I can't find anything else online about this. This raises the possibility of putting a film-bourne virus in a movie or trailer, though I'm not totally sure what you could really do by pwning a sound processor.

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Dynamic loading was indeed a software update of the processor using the data carried on film. If a film contained an update, it would be contained at the start of a film. The processor would detect this, read the software update, reboot (and revert into mono analogue audio for this) and then continue off using the updated software.

There are 3 blocks every 128 on the film that contain the software update (and/or other data channels, or are unused). They're also used for something called the "Splice cache" which I can discuss if you want. The rest are the audio blocks.

As far as I'm aware, Dolby only used this once - to update from what they called version EC9 to EC11. I've also heard that it didn't work well with the DA10 - their first processor - and this may be part of the reason.

thank you for sharing your knowledge

Is the "splice cache" used to cover for discontinuities (e.g. reels spliced together for the entire film, cuts to remove damaged sections...)? I'm just guessing from the name here.

Indeed it is! Films come on 20 minute reels, and from the late 80s onwards were spliced together onto one big reel (or platter) for playback. However the splice often wasn't perfect, and the reel ends are most likely to contain dust/dirt/scratches, which could knock out the digital audio and revert playback to the analog track. This obviously isn't ideal, so Dolby had the idea of encoding the area at the end of each reel throughout the entire reel too, which is stored in a cache in the processor. Then, when the end of the reel is reached (you can tell this because each block has a sequence number), the processor uses the cached data to ensure a nice changeover.

The Wii used this technique - game discs included the latest version of the system software, so that consoles would get updated by buying new games even if they were never connected to the internet.

I think that was quite common in that era. I’m sure my (banned) 360 would still update from game discs. Not sure on the ps3 though.

You could replace the THX sound with "never gonna give you up".

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