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I don't understand all this confusion about what RT means, this is the definition of a RT system. If you can't complete the computation within the given deadline whatever partial result is discarded and the computation starts from scratch.

Decoding video and interactive rendering is a great example of an RT system. If you can't construct a frame within (usually) 16 ms you skip it and start with the next one.

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There is a difference between hard real time and soft real time. Hard real time systems mean that missing a single deadline may be a crash, whereas a soft real time system, missing a deadline just causes a degradation. Video is definitely soft real time.

Hard and soft real time depend entirely on the context. An example of hard real time is flight control. The whole sensor - actuator - decision process must happen within the given threshold.

But decoding video in practice isn't usually realtime because you still have to do it when you don't have kernel support and are at the whim of your kernel's scheduler which is basically always.

It's a good example of a problem where a realtime system would be useful but it's not a good example of a real-life realtime application (usually).

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