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Digital VHS - not satisfactory

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Old 08-09-2007, 08:36 AM   #31  
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Originally Posted by Chris Gerhard View Post
There are two kinds of DVR's, one that encodes an analog signal, without question there is a difference and the difference can be huge when encoding at a low bitrate. The other kind that directly records a digital signal, records the bitstream and there is no difference. I don't know where you think the two of us differ.
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Yes, Chris and I are in agreement on this. The DirecTV DVR is recording the digital signal directly to disk. When you play it back, you're getting the same 1s and 0s that you would get if you watched it live.
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Old 08-10-2007, 06:33 AM   #32  
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We don't disagree Chris.

It's Coleman with whom I disagree.

Last edited by electrictroy; 08-10-2007 at 06:44 AM..
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Old 08-10-2007, 06:43 AM   #33  
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Let's back-up to the original statement I was refuting:
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Originally Posted by rcoleman11 View Post
Also, unlike a VCR, there is no difference in quality between watching a live program and a [DVR] recording.
I disagree.

- If the "live program" is analog, as is the case with my cable supplier, there will be loss as the DVR compresses the image & tosses away information.
- Plus if the "live program" is analog, SVHS can do just as good a job as DVR in capturing the signal. SVHS can easily capture the 330-line resolution of analog signals.


Perhaps you should have specified, "when recording digital..." if that's what you intended to say. That's why I didn't understand because you left-out that key phrase. I was thinking we were discussing analog "live programs" as that is what my cable supplier uses.
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Old 08-10-2007, 07:32 AM   #34  
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Originally Posted by electrictroy View Post
Let's back-up to the original statement I was refuting:
I disagree.

- If the "live program" is analog, as is the case with my cable supplier, there will be loss as the DVR compresses the image & tosses away information.
- Plus if the "live program" is analog, SVHS can do just as good a job as DVR in capturing the signal. SVHS can easily capture the 330-line resolution of analog signals.
Nope, a TiVo such as my HDR212 at highest quality will do better recording a good analog signal than SVHS at SP in my opinion. My Panasonic Showstopper ReplayTV at highest quality will do the same. I have proven this to myself with tests many years ago. You can do the same if you get a DVR. I don't know about the longer recording times, I don't use them but I have used the best settings with all the recorders I own extensively. I don't worry about recording analog much anymore other than one DVR that is set to record "Get Smart" and a few movies from TCM over analog cable. High bitrate MPEG-2 does great with analog signals in my opinion. Now you certainly need a huge amount of storage to record much at the highest settings, but large capacity IDE hard drives are inexpensive now. You could use two 150GB drives with a TiVo like the old one I use or even higher capacity drives with the newer ones. My old TiVo and old ReplayTV can only use 137GB on each drive.

I also believe ATSC OTA can look great. I don't know what most local stations do, maybe compress it and include several subchannels and the result is awful, but it doesn't have to be that way. I have recorded some ATSC HD OTA to D-VHS and it looked terrific. I have also recorded some highly compressed OTA signals that don't look very good at all.

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Old 08-10-2007, 09:04 AM   #35  
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Originally Posted by electrictroy View Post
Let's back-up to the original statement I was refuting:
I disagree.

- If the "live program" is analog, as is the case with my cable supplier, there will be loss as the DVR compresses the image & tosses away information.
- Plus if the "live program" is analog, SVHS can do just as good a job as DVR in capturing the signal. SVHS can easily capture the 330-line resolution of analog signals.


Perhaps you should have specified, "when recording digital..." if that's what you intended to say. That's why I didn't understand because you left-out that key phrase. I was thinking we were discussing analog "live programs" as that is what my cable supplier uses.
DirecTV DVRs (like the two I have) are entirely digital. There is no analog. It records the bitstream onto disk and, when you play it back, you are seeing exactly what you would see if you watched it live. Nothing is thrown out - it's the same 1s and 0s.

Your assertion that "Super VHS produces programs identical to the live broadcast" is incorrect. Super VHS is analog and a copy will never be identical to the original.
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Old 08-10-2007, 10:38 AM   #36  
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Chris: When I recorded my analog cable to the D-VHS (which operates similar to DVR with analog-to-MPEG2 encoding), the result did indeed look "very clean". But that was more of a drawback than an advantage, because it made the DVHS recording look artificial, rather than live. It was obvious I was watching a recording.

BTW do any of the DVRs have the capability to convert a ~28 Mbps ATSC stream into a ~7 Mbps stream (i.e. digital-to-digital conversion)?
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Your assertion that "Super VHS produces programs identical to the live broadcast" is incorrect. Super VHS is analog and a copy will never be identical to the original.
(1) I meant that it APPEARS identical. I can't see the difference between SVHS and a "live" show from Comcast. (Really, honestly, I can't.)

(2) Neither is digital perfect. Bit-errors are rare but they do happen. (And of course the lossy compression means you've already lost picture and sound information, right from the start.)

Last edited by electrictroy; 08-10-2007 at 10:44 AM..
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Old 08-10-2007, 10:57 AM   #37  
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Chris: When I recorded my analog cable to the D-VHS (which operates similar to DVR with analog-to-MPEG2 encoding), the result did indeed look "very clean". But that was more of a drawback than an advantage, because it made the DVHS recording look artificial, rather than live. It was obvious I was watching a recording.

BTW do any of the DVRs have the capability to convert a ~28 Mbps ATSC stream into a ~7 Mbps stream (i.e. digital-to-digital conversion)?

(1) I meant that it APPEARS identical. I can't see the difference between SVHS and a "live" show from Comcast. (Really, honestly, I can't.)

(2) Neither is digital perfect. Bit-errors are rare but they do happen. (And of course the lossy compression means you've already lost picture and sound information, right from the start.)
No DVR I am aware of can compress a 28Mbps data stream to 7Mbps. No DVR I am aware of can do anything but record the exact stream. What I don't know is what happens with a bitrate that exceeds the DVR maximum. I don't have an access to data like that and I don't think I ever will, in other words my DVR can handle far greater bitrates than I can get with cable, satellite, and OTA. I don't understand your opinion with SVHS versus the D-VHS MPEG-2 encoding, but accept that it is your opinion and is what you see. SVHS is a good quality NTSC recorder.

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Old 08-11-2007, 12:30 PM   #38  
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(2) Neither is digital perfect. Bit-errors are rare but they do happen. (And of course the lossy compression means you've already lost picture and sound information, right from the start.)
Any loss due to compression occurs before it ever gets to the DVR. The bitstream that is received by the DVR is recorded to the disk and is same as what you get when you play it back. You have posted so many erroneous comments it's hard to even keep track of them. Now you are backpedaling and trying to confuse the issue by asserting facts that have nothing to do with the issue under discussion. Get a clue.
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Old 08-13-2007, 12:35 PM   #39  
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Any loss due to compression occurs before it ever gets to the DVR.
No shit Sherlock.
I never claimed otherwise.

Nevertheless the image IS compressed, which is why I see macro-blocking and "mosquitos" floating around, even in a live ATSC picture.
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Old 08-13-2007, 01:11 PM   #40  
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There are two kinds of DVR's, one that encodes an analog signal.....
IMHO if a DVR can encode analog shows, and also has the ability to decode the digital data for display on an analog set: It should be able to change bitrates on the fly. First decode the 28 Mbps bitsteam, and then reencode it at some lower rate like 7 Mbps.

Perhaps no DVR maker thought to include that capability, but it seems a logical step for those desiring to record 400 hours of SD-quality, rather than just 40 hours of HD.
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Old 08-13-2007, 03:05 PM   #41  
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Nevertheless the image IS compressed, which is why I see macro-blocking and "mosquitos" floating around, even in a live ATSC picture.
Well, there you go again - asserting the same irrelevant piece of information as if it will somehow cover up your previous misstatements and your lack of knowledge of the subject.
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Old 08-13-2007, 03:24 PM   #42  
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Originally Posted by electrictroy View Post
IMHO if a DVR can encode analog shows, and also has the ability to decode the digital data for display on an analog set: It should be able to change bitrates on the fly. First decode the 28 Mbps bitsteam, and then reencode it at some lower rate like 7 Mbps.

Perhaps no DVR maker thought to include that capability, but it seems a logical step for those desiring to record 400 hours of SD-quality, rather than just 40 hours of HD.
.

I don't know what complications exist to use variable bitrate encoding, probably far more processing power than is being used for starters. Of course as I mentioned the DVR's that record the exact bitstream do record variable bitrate streams since that is what satellite and cable use. Somebody with a better technical understanding than I have would have to explain the reasons behind what is being done. Keeping the equipment affordable is likely the easy answer.

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Old 08-20-2007, 08:26 AM   #43  
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I think you're right Chris. It is technically feasible to decode 28 Mbps and then reencode it at 7 Mbps, but would also be expensive..... and most DVR makers want to keep their product as cheap as possible.
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Well, there you go again - asserting the same irrelevant piece of information as if it will somehow cover up your previous misstatements and your lack of knowledge of the subject.
The fact that video has to be compressed before transmission is NOT irrelevant.

And anyone who claims "no loss" (as you did) is putting-forward an inaccurate statement which misleads newbies to think DTV is an uncompressed signal.

Last edited by electrictroy; 08-20-2007 at 08:31 AM..
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Old 08-20-2007, 11:32 AM   #44  
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The fact that video has to be compressed before transmission is NOT irrelevant.

And anyone who claims "no loss" (as you did) is putting-forward an inaccurate statement which misleads newbies to think DTV is an uncompressed signal.
The only inaccurate statements in this thread are yours. All MPEG video is compressed, which has nothing whatsoever to do with the fact that what is recorded to disk by the DVR is identical to the live feed - i.e., there is no loss of quality. What I stated is 100% accurate. If there's a newbie reading this thread, it's you.
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Old 08-20-2007, 02:50 PM   #45  
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what is recorded to disk by the DVR is identical to the live feed - i.e., there is no loss of quality.
FALSE statement. (And if you were engineer, you would no why it's a false statement.)
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