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Comment by detaro | Hacker News Reader

What percentage of the market is A/V build to actual hard real-time standards, and not expected to run on devices that can't provide it (so no PCs with normal OSes, no smartphones)? For the vast majority, soft real-time is fine, since an occasional deadline-miss results in minor inconvenience, not property damage, injury or death.

I assume some dedicated devices are more or less hard real time, due to running way simpler software stacks on dedicated hardware.

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I take it that scarcely anyone here has written software for video switchers, routers, DVEs, linear editors, audio mixers, glue products, master control systems, character generators, etc. etc. Missing a RT schedule rarely results in death, but you'd think so given the attitude from the customer. That's a silly definition for it.

There's a whole world out there of hard real time, the world is not simply made up of streaming video and cell phones.

The cool thing on HN is you can get down voted for simply making that observation. It's a sign of the times I'm afraid.

You just agreed with the OC.

RT video/audio failing never results in death. Where as failures in "avionics, industrial control" absolutely can / do. That seems to be where OC was drawing the line.

Seems to be a common distinction, although GP is right with the addition that the production side of things is more demanding (and at least would suffer financial damage if problems occur to often) than the playback side formed by random consumer gear, and has some, especially low-level/synchronization-related, gear to hard standards. But often soft is enough, as long as it's reliable enough on average.

I actually have written software for video routers and character generators. We didn't consider them hard real time, though I wouldn't claim that such was standard industry usage.

For example, if you're doing a take, you have to complete it during the blanking interval, but usually the hardware guarantees that. In the software, you want you take to happen in one particular vertical blanking interval (and yes, it really is a frame-accurate industry). But if you miss, you're only going to miss by one. We didn't (so far as I know) specify guarantees to the customer ("If you get your command to the router X ms before the vertical interval, your take will happen in that vertical"), so we could always claim that the customer didn't get the command to the router in time. Again, so far as I know - there may have been guarantees given to the customer, but I didn't know about them.

But that was 20 years ago, back in the NTSC 525 days.

Nice name, by the way. Do you know of any video cards that will do a true Porter & Duff composite these days? I recall looking (again, 20 years ago) at off-the-shelf video cards, and while they could do an alpha composite, it wasn't right (and therefore wasn't useful to us).

I currently work on software controlling the hardware like video routers, and this is definitely my experience. It’s all very much soft real-time.

In terms of customers and how much they care, the North American market seems to care less than Europe.

I work on an open-source music sequencer (https://ossia.io) and no later than two days ago I had a fair amount of mails with someone who wanted to know the best settings for his machine to not have any clicks during the show (which are the audio symptoms of "missed deadline"). I've met some users who did not care, but the overwhelming majority does, even for a single click in a 1-hour long concert.

If it's running in a consumer OS (not a RT one) and it counts on having enough CPU available to avoid missing the deadline, that's exactly what soft-realtime is.

Compare your “not a single click in an hour [for quality reason]” to a “not a single missed deadline in 30 years of the life expectancy of a plane, on a fleet of a few thousands planes [for safety reasons]”. That's the difference of requirements between hard and soft RT.

I did some soft real-time (video decoding) and I have a friend working on hard real-time (avionics) and we clearly didn't worked in the same world.

Yeah. To me, hard real time is when you count cycle (or have a tool that does it for you), to guarantee that you make your timing requirements. We never did that.

>For the vast majority, soft real-time is fine, since an occasional deadline-miss results in minor inconvenience, not property damage, injury or death.

A "minor inconvenience" like a recording session going wrong, a live show with stuttering audio, skipped frames in a live TV show, and so on?

As long as the individual event happens seldom enough few of these actually are a big problem. Soft real-time being allowed to blow deadlines doesn't mean it can't be expected to have a very high rate of success (at least that's the definitions I've learned), and clearly a sufficiently low rate of failure is tolerated. There's a vast difference between "there's an audio stutter every day/week/month/..." and "noticeably stuttering audio". The production side is obviously a lot more sensitive about this than playback, but will still run parts e.g. on relatively normal desktop systems because the failure rate is low enough.

The production side usually renders the final audio mix off-line, so no real-time requirements there for getting optimum sound quality. I'd say the occasional rare pop or stutter is worse to have during a live performance than when mixing and producing music.

Most professional recording studios are using consumer computer hardware that can't do hard realtime with software that doesn't support hard realtime.

People like deadmau5, Daft Punk, Lady Gaga all perform with Ableton Live and a laptop or desktop behind their rig. If it were anything more than a minor inconvenience, these people wouldn't use this.

It's very unlikely to have audio drop outs, a proper setup will basically never have them. But still if you have one audio dropout in your life, you're not dead, your audience isn't dead, a fire doesn't start, a medical device doesn't fail to pump, and so on.

And yes you can badly configure and system, but the point is you can't configure these to be 100% guaranteed, 99.99% is perfectly fine.

Edit: Sometimes people call these "firm" realtime systems. Implying the deadline cannot be missed for it to operate, but also that failure to meet deadlines doesn't result in something serious like death (e.g in a video game you can display frames slower than realtime and it kind of works but feels laggy, however you cannot also slow down the audio processing because you'll a lowered pitch, so you have to drop the audio.)

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