Question about hard drive space/compression

[jerry814]

hello all,

i am a relatively new subscriber to dish network and have a 625 box. i have noticed (as have many others in these forums) that my local channels show far more evidence of mpeg2 artifacting (blocks and blurs) than national cable channels. movie channels seem to be of the highest quality. this leaves me with three questions:

1. i'm assuming that e* is devoting more bandwidth to the premium channels, and then the national channels, and then the least to the locals because the fewest people get them. is that a fair assumption?

2. if the above is true, then wouldn't it make sense that if i record "cheers" off a local channel it would take up less space on my hard drive than if i recorded it off tvland? i know that the space indicator only gives a "time remaining" indication, and as yet i haven't watched it closely enough to notice if a full 30 minutes comes off for each show, but i'm guessing that is the case. so is it padding the stream to take up the full amount of space, perhaps even re-encoding a low-bitrate stream to a high-bitrate one (which will obviously not make it look any better)? or is it actually saving that space somehow? or, i suppose it's possible that the locals get the same bandwidth but look worse because whatever mpeg2 compressor is running on them isn't able to process as fast as the one in use for the national feeds, and thus outputs a poorer quality image at the same bandwidth?

3. i know that the locals are mirrored to the broadcast channel numbers (channels 2, 11, 13 etc. in houston) from a channel number somewhere in the 8000s. is that a straight channel number swap, or is the feed potentially different (ie, coming from a different satellite), and thus possibly one feed is possibly better than another?

many thanks for any help with this. i've only used this forum for a month or two now, and it has already been of immense help to me. you guys are providing a great service here.

 

[Mr Tony]

3. i know that the locals are mirrored to the broadcast channel numbers (channels 2, 11, 13 etc. in houston) from a channel number somewhere in the 8000s. is that a straight channel number swap, or is the feed potentially different (ie, coming from a different satellite), and thus possibly one feed is possibly better than another?

actually they are remapped. The legit channels are between 7000-9400 because thats there legit spot. Older receivers can't map them to the new channel (3,6,8,etc). Obviously dish cant use 3,6,8 as their normal channels because how many channel 8's are around the US? Mine are in the 7574-7581 but are remapped to 3,6,8,10,11 7 21 in my 301. On the old 5000, they are 7574-7581.

Its the same channel and doesnt use anymore bandwidth.

 

[phat_bastard]

2. if the above is true, then wouldn't it make sense that if i record "cheers" off a local channel it would take up less space on my hard drive than if i recorded it off tvland? i know that the space indicator only gives a "time remaining" indication, and as yet i haven't watched it closely enough to notice if a full 30 minutes comes off for each show, but i'm guessing that is the case. so is it padding the stream to take up the full amount of space, perhaps even re-encoding a low-bitrate stream to a high-bitrate one (which will obviously not make it look any better)? or is it actually saving that space somehow? or, i suppose it's possible that the locals get the same bandwidth but look worse because whatever mpeg2 compressor is running on them isn't able to process as fast as the one in use for the national feeds, and thus outputs a poorer quality image at the same bandwidth?

The time remaining indicator is just a general freespace indicator. I'm not sure exactly how it's computed, but when your recordings partition has 0% used it will show 100 hours. You raise a good point about the locals and compression. I'm sure you would be able to get quite a bit more on it if you were recording only locals or something that compresses well like cartoons. You can never truly fill the drive however, because the dvr makes sure it has about 5 gb for the live tv buffers at all times.

 

[Anole]

I sometimes note the actual data rate or number of gigabytes for a show, and they do vary by channel.
I -think- if you have any of the national feeds in the 200-260 (?) range, they might be of better quality.
I hardly ever watch locals, but when I do, I don't notice any visual problems.
My locals -are- the national feeds, so I never see the heavily compressed locals some folks complain about.

What size and type is the TV you are watching on?

As for the number of actual hours you can get on any particular size hard drive, search these forums for comments.
I know I've posted some actual numbers for 501/508/510's, and those should be scalable or applicable to your PVR.
The number of hours/shows is well under that advertized, but the PVR family are still great to have.

.

 

[jerry814]

thanks for all of the info. that helps clear up my questions. if anybody has anything else to add, i'm always curious to learn more.

 

[Bob Haller]

LIL PQ can be effected by the quality or lack thereof the station, how good the backhaul is, how its collected for backhaul, direct fibre vs OTA antenna, the bandwidth allowed by E, and that varies on the fly per transponder. if a bunch of stations all on the same transponder happen to have say a basketball game, artifacting can occur.

My LIL PQ is pretty good, but occasional pixeling does occur...

 

[Anole]

compress this !

I just had a long discussion on this subject with an ex-TV engineer from Los Angeles.
He has moved away from there, but still gets LA on sat, plus gets the networks delivered by a local station.
He says LA networks are uplinked via network satellites running 8-10 megabits per second, for delivery to out of town network stations.
So, they'll have about the same satellite lag time delay Dish has. *
He was comparing that to his Dish reception, and claimed Dish was much worse.
From my study, I'd say networks are running around 2 to 2.3 mega bits per second on Dish.

The picture problems he describes, I really haven't seen.
Fade all picture to black (or maybe cut to black) tears up Dish, he says.
I edit those shows sometimes, and I sure don't see it.

I won't say he's wrong, but as an ex-tv engineer, who's worked with hi-def, I wonder how hypercritical he might be?


* He was counting maybe three seconds lag between his local station over the air, and Dish.
That, he said, was a sign that Dish probably had good encoders trying to do the right thing, making mpeg.
And the fact that they don't have good stuff coming out, was just due to crowding too much data into the transponder.
(in other words, it didn't all get through)

We surmised that maybe some little city with 100k people might get even worse compression of their locals than LA or NY, but we don't have the data to back that up.

 

[SimpleSimon]

Go to www.dishchannelchart.com or www.lyngsat.com and count the channels per transponder to see what's what.

Last I looked, Colorado Springs locals per on a TP that had a total of only 7 channels. PQ is as good as can be expected anywhere. Other DMAs might be stuffed on TPs with as many as 12 channels - that's going to dgrade things for sure.

 

[Big Bob]

Last I looked, Colorado Springs locals per on a TP that had a total of only 7 channels. PQ is as good as can be expected anywhere.

Unless they compress them at the POP before the backhaul to the uplink site. My guess is that Dish is saving pennies by doing some pretty heavy compression before they backhaul them. After that, it really doesn't matter if each channel is on it's own transponder, it will never look all that great.

does anyone know how dish is compressing the locals before they backhaul them? Even worse, are they compressing them before the backhaul, decompressing them and then recompressing them before uplink