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 Drives & DVRs: Filesystems

This is the second post in the series on hard drive selection for DVRs. The first post talked a bit about the type of workload that a DVR imposes on the drives and went through some basic ways of measuring raw drive performance.

In this post we’ll take a look at the impact that the filesystem has on I/O performance, again with an emphasis on a DVR recording and playback workload. The filesystem is one of a few system components that we have some control over and that has a great impact on how the drive behaves.  The I/O scheduler is another component that we’ll take a look at in a subsequent post. Continue reading “Hard Drives & DVRs: Filesystems”

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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Do You Need a VHF Antenna?

I’ve been in Las Vegas this week for the Amazon re:Invent conference. While there are enough sessions, receptions, and parties to keep you occupied day and night, I just couldn’t pass up a chance to check out the Las Vegas OTA airwaves. The Vdara staff was a bit mystified by my request for the highest south-facing room I could get, but very accommodating. So here I am on the 49th floor with good line-of-sight to the major towers (and a view of the desert instead of the Bellagio fountains, which apparently most people ask for.)

I had packed up a full Entangle development setup, including my trusty Silver Sensor antenna (aka the Zenith ZHDTV1). What I failed to do while busily packing was to check the RF frequencies of the Las Vegas broadcasts. As it turns out there are a few major channels in the VHF bands, including one on channel 2. Sadly the Silver Sensor is a UHF-only antenna.

This brings up an interesting point regarding the current state of OTA antennas: many of them, particularly the compact ones, are UHF-only. Even the ones that claim to be both UHF and VHF don’t handle VHF very well. At best they’ll pull in VHF-Hi. But can you make do with a UHF-only setup?

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