Thursday, December 13, 2012

Data Rates Required To Feed 1080p HDTV?

I have been wondering if it was finally time to buy an HDTV to replace the CRT low-res TV we currently have.  I was watching PBS' Blue Planet a couple of nights ago, and I noticed a lot of pixellation in the video.  This isn't the missing difference frames problem that you often see with MPEG, where losing a packet or two causes random patches of color; this is the problem where you get fairly consistent patterning, I believe caused by the receiver signalling to the sender that it needs to slow down data rates, and it does that by substituting a lower data rate stream which does fewer of the wavelet compression thingies that are how JPEG/MPEG and similar compression schemes work.

It suddenly occurred to me: might my data rate be too low to fully take advantage of 1080p HDTV.  Theoretically, I am paying for a 5 Mbps downstream data rate, but we all know that this a nominal rate, and what you actually get is dependent on many things that are beyond the ISP's control.  Sure, the broadcast digital signal would be sufficient, and we do have a BlueRay player as part of our current setup, but since the vast majority of what we watch is Netflix, might HDTV turn out to be a pretty minor gain when our Internet connection is only nominally 5 Mbps?

9 comments:

Rob K said...

I have 5Mbps DSL, which frequently in the evenings of late speedtest.com tells me is only providing 0.3Mbps. Even at that rate Netflix on my Visio TV runs OK. When we have at least 0.5Mbps, we don't have any problem running 2 Netflix streams and I don't notice any degradation. If it drops too much, Netflix just rebuffers. Of course most of what we watch isn't in HD. I haven't really seen what you're describing. What kind of box do you have feeding your TV? That might actually be the culprit.

Clayton said...

It is an obscure off-brand whose name I do not remember. Oddly, I have only seen this on Blue Planet, or at least this is the only place that I have noticed it. Perhaps it an artifact of the 2001 vintage of the series; not well encoded?

TMLutas said...

Go to speedtest.net to test your bandwidth. I have no financial stake in them but they seem to be pretty trusted.

saltrifle said...

Most streaming video is significantly compressed from the blue-ray or original signal. Hence your bandwidth should be fine.

Mauser said...

Blockiness without dropouts is consistent with over-compression. It might not be the sender, but the source material might not be available in a higher data rate. This is especially true of "Expanded basic" tier channels.

Sigivald said...

I find I really do get advertised rates almost all the time with my DSL (CenturyLink, in Oregon) - though naturally because of protocol overhead on three layers (TCP in PPP in Ethernet in ATM) 7 megabits "for real" over the wire ends up being 5 megabits of useable TCP bandwidth.

Given compression, there's no reason that you shouldn't be able to get at least 720p-level HD signals over a 5mbit link.

h264 1080p24 can in theory fit in about 5mbits, streaming, still at very high quality.

Knock that down to 720 and/or add more compression, and it should easily fit in your pipe.

paul a'barge said...

Get the 1080P HDTV and then (and I mean immediately) get a Blu-Ray player.

Then get some Blu-Ray discs. I love the Nat-Geo Yosemite disc.

And the whole thing will immediately make sense.

Clayton said...

I noticed last night that the peculiar artifacts that I was seeing ONLY appear in the underwater sequences.

Alcibiades said...

Are you viewing the television at an angle? Because I get splotchiness on certain colors (particularly blue) when I look up at my HDTV.

If this is the case, it's not your connection. HDTVs have a shallow vertical viewing angle (compared to my old LCD monitor). It may vary by manufacturer, but I can't be sure.

Adjusting the angle (or your position) will cause it to go away. Alternatively, adjust the contrast until it seems to be gone (but in that case, it's difficult to get it to look *just* right).

And now I just re-read your post and noticed that you don't have an HDTV, so now I'm at a loss for what's happening.