Revisiting SSDs in DVRs

Previous posts at in-koherence have been rather skeptical of using SSDs as recording storage in DVRs. SSDs have a lifespan that is largely dictated by the amount of data written to them. This may not be much of a problem if you record one or two shows a day. However many users set up recordings for series which they might watch (but for some reason never find the time to…or maybe they decided it wasn’t such a great series after all, but who has time to cancel the subscription to the series?) This is amplified if multiple members of the household set up recordings on the DVR. The next thing you know it your four-tuner DVR is recording 20 hours of shows a day. For all its faults, the good old mechanical hard drive is superior in having a write limit that’s so high that it’s generally not considered.

But with rapidly falling prices, larger capacities (with correspondingly higher endurance ratings), and the increasing difficulty of finding non-SMR 2.5″ hard drives, the time has come to give SSDs a harder look. So we took a mid-grade SSD and ran the first SSD-based Project Entangle through its paces.

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Enhancing OTA ATSC Reception Through Diversity

One of the goals of Project Entangle is to receive The Perfect Broadcast – a transport stream with no bits missing or in error. As anyone using OTA ATSC (and since you’re reading this you’re probably one of them) knows, this can be a challenging endeavor. Signals can be too weak, and ironically too strong. Multipath can turn an otherwise strong  signal error-prone. Dynamic multipath is even harder to deal with as the demodulator needs to adapt to the changing properties of the signal.

But hard doesn’t mean impossible. One of the methods for obtaining The Perfect Broadcast that Project Entangle has been investigating is diversity. Essentially, diversity involves receiving two or more versions of a broadcast in different ways. The various versions are then combined to yield a signal that’s better than any of the individually received ones.
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Update: The SiliconDust HDHomerun Connect Quatro

I’d like to thank all of you who commented or emailed about the SiliconDust HDHomerun Connect Quatro review posted in November of last year. I’m truly amazed at the amount of interest it garnered.

And there’s some great news for those of you who have the Quatro or been on the fence about getting one – the issue reported in that review has been addressed with the 20180327 firmware!

The HDHR5 Quatro now performs on par with the HDHR4 Connect. In fact, for certain types of impairments, it may perform a bit better.

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MPEG-2 Video Error Concealment

A lot of effort goes into making sure that the episode of America’s Funniest Home Videos you watched last night was as pristine as possible. From the network’s broadcast center to your local TV station’s transmission tower to that antenna on your roof, and finally to your DVR, a number of mechanisms ensure that all those 1s and 0s in the digital broadcast get to you unscrambled and in the right order.

But from time to time lightning storms, swaying trees, and stray cats will wreak havoc on the signal. Filters, error detection and correction codes, and even the most elaborate incantations of RF engineers struggle to make sense of the distorted waveform being received.  Inevitably the occasional glitch sneaks past and you end up recording some damaged audio and video.  The last bastion of defense for couch potatoes lies in the MPEG decoder and player’s ability to try to make some sense of the damaged programming. In many cases some sleight of hand can mitigate the visual effect of the damage, and occasionally the errors can be concealed so well that they’re invisible to the casual viewer.

We’re going to focus in this article on error concealment of MPEG-2 video. But the general principles apply to other video compression schemes such as H.264 and H.265.

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Hard Drive Selection for DVRs

This and the next few posts will be focusing on hard drive selection for DVRs. This post will look at the type of workload that a DVR imposes on drives, using Project Entangle as an example. Subsequent posts will look at various system characteristics that can affect performance and performance measurements from some drives. And we’ll take a special look at shingled magnetic recording (SMR) drives, as they tend to have some very peculiar performance characteristics.

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