What Are The Differences In Lines Of Resolution Between Broadcasted And Recorded Video Sources?

Since I haven't had a chance to respond to the original topic I'll start there First off, let me start with a disclaimer. Despite what my guides and some of my posts may suggest, I haven't been working with video for very long. In fact besides being able to follow some simple instructions, I didn't know much of anything until about a year and a half ago when my computer died from a lightning strike and I got a replacement from the insurance company that had a capture card. I've learned a lot about digital video since then, mostly because I had to figure out CCE SP, and you can't really make good use of it without understanding quite a bit. I've never read any books or taken any classes on it, and my only sources of information have been from the internet and my own personal experiences with it. That may surprise some of you, but trust me, I learn more from others here (and other places) than anybody learns from me. I just happen to pick it up quickly and make a lot of good deductions.

Analog video, on the other hand, is more like PFM to me. Since my capture card uses a hardware encoder, and there is almost no software besides what came with it that can control it at all, I've learned a lot less about the subject. I understand the basics, mostly from reading and re-reading (and re-reading and re-reading) the articles, guides, posts both on and linked to from Doom9. I won't pretend to know as much about the resolution of different analog video sources as others here, but I will share what I've personally observed and the conclusions I've drawn from it. I wouldn't be surprised to find that I've come to some incorrect conclusions, so please correct away.

You should be happy with that Sophocles - already a long post and I haven't said anything yet ;-)

Let me start by restating and expanding on the point I was trying (ineffectively) to make in the other thread. I believe it's inaccurate to say that all analog (SDTV) captures are no better than VHS quality. That's not to say that they're DVD quality, because I have yet to see one I wouldn't be able to distinguish from a correctly transferred and encoded DVD of the same material. When I say analog captures, I'm not talking exclusively about video that's been purely analog from beginning to end. I also include digital cable and satellite signals that have been decoded for display on a TV. Since neither receiver I used to use for digital cable and the ones I currently use for satellite reception have any digital outputs, I've done a lot of experimenting with both formats, and have been able to make visual comparisons of both to analog cable and VHS.

Let's start with the VHS since (IMO) it's clearly the lowest quality of the lot. Many people think exclusively about the amount of information that can be stored on a video tape, which is clearly not anywhere near the equivalent of D1 resolution, but this is really not the only problem with capturing from that medium. The worst flaws from VHS (once again IMO) are from the physical characteristics of the tapes and the playback mechanisms. The susceptibility of tapes to wear and tear, and the differences between one VCR and another (at least those anywhere near my budget) lead to picture distortion that I find very annoying, and as a result those things catch my eye immediately. For more informative discussion of capturing VHS than I could ever hope to provide I recommend reading this thread: http://forum.doom9.org/showthread.php?s=&threadid=34122 I don't pretend to understand where a lot of the calculations come from, but for anyone interested in testing things for themselves (or getting information from knowlegdable people who have) it's a good place to start.

Then there's analog cable. Since there's not consumer level video tape playback involved (hopefully), some of the playback flaws are all but eliminated. I know next to nothing about the actual amount of information stored in these signals, but I will say that I find them to be higher quality than what I got from most channels I had on digital cable, but that's due to the bandwidth limitations intentionally imposed by the cable company in order to provide internet service. Cable signals have their own physical problems from being transmitted long distances. Obviously, the signal can never be better than what the poorest section of transmission media allows, and of course most people have substandard media in their homes anyway. Additionally, since this is a purely analog transmission, some of the signal will be replaced by noise, and if it needs to be amplified, the noise will be amplified along with the signal.

Digital cable is, in theory, a better approach. Being a digital signal that's just transmitted in analog, it can be periodically repeatered to avoid signal loss. Unfortunately, digital cable normally means cable internet as well, so the bitrate of the signal is compromised in order to save bandwidth for internet service. As a matter of fact, I found that on the local system here, premium channels had enough flaws that they were often unwatchable. I've never looked into what the resolution of a digital cable signal is, but I do know it's often higher than it should be for the bitrate used for transmission. Whether that's because it's encoded with that bitrate in mind and that causes the picture quality to suffer or it's encoded at a reasonable bitrate for the resolution and information is lost due to a lack of transmission bandwidth I don't know. To be honest, I didn't understand digital video nearly as well when I had cable, so I just didn't think too much about it at the time. Like analog cable, the signal can also suffer due to poor transmission media at any point from the origin to your receiver.

Satellite television (standard definition) has higher quality than any comparable cable signal (and certainly any VHS signal) I've ever watched. It's sharper, and barring interference from atmospheric conditions (or solar flares) it has a lower occurence of artifacts that can be clearly traced either to lack of bits for encoding or loss of bits to be decoded. The exact resolution for the 2 major satellite services in the US (DirecTV and Dish Network) seem to be closely guarded secrets, but from the research I've done it seems that either 480x480 or 540x480 is used for nearly everything, although it's possible that pay per view programs may use higher resolutions than that, and from the few I've seen myself, they certainly have higher bitrates than regular programming or premium channels. Likewise, the bitrate seems to vary among the regular subscription channels. My biggest dissapointment with Dish Network has been their paranoia about computer based receivers, which is the only reason I can't get a capture card that would allow me to save the data stream directly to my PC.

As I mentioned, my captures were done with a Sony hardware MPEG encoder. The encoder chip used is one that's also used in standalone PVRs available in Japan, but not the US. It captures at 352x480 or 720x480, and can capture at a bitrate that far exceeds what either digital cable or satellite signals are encoded at. For most of my captures I connected the S-Video and RCA audio outputs from the back of the receiver directly to my PC. For analog cable I connected the cable directly to a VCR and used that for a tuner (to avoid interference from the PCI bus which causes problems for the internal tuner), connecting the RCA video and audio outputs to the PC.

The biggest flaw it has is an intra DC precision of 8, which is DVD compliant, but not as high as the maximum compliant value of 10. There's very little information available anywhere about this card, and pretty much all of it is in Japanese. Initially I was only able to find a page that referenced the MPEG encoder chip (by searching for the part number) being used in the Sony standalone PVR. Eventually I ran across it referenced with the name YUZU, and was able to find a little more information, but not much of any real use.

My initial captures were done from cable. The channel I was capturing from looked pretty good when using the digital cable signal, but overall the quality was much better from the analog version. Mostly it was just a question of consistency. The best parts looked better from digital, but the analog quality rarely fluctuated. Neither was particularly sharp.

When I replaced my cable with satellite service I kept capturing from the same channel, but the signal was much sharper, and had a lot more detail. There were still times when it didn't look good, but I could always trace those to reception issues. Aside from occasionally not having any signal, the video is always better than my cable ever was. When I was doing a lot of experimenting, I even captured a pay per view movie, and the results were amazing. I'd compare it to laser disc quality. Obviously that's not representative of the quality of most programming, but it's definitely possible.

Before I wind up this already long winded post, it's worth mentioning that when I discovered that my card only encoded with an intra DC precision of 8 I figured there wasn't any point in re-encoding with an intra DC precision of 10 because that would be trying to get more detail than the source. I did a lot of testing trying verify that, and I was surprised to find that in every case, setting it to 10 in CCE resulted in a higher quality encode. To me that's significant because it means that a good encoder can do a better job of filling in the "missing" details than my TV. This may not apply to better TVs, but it seems to apply to mine.

And with that I'll wrap up my dissertation ;-)

 

Or dreading ;-) Maybe I should have divided it into chapters.

Oh, and thanks to everyone for cleaning up the other thread. I realize it's far from the only one that's gotten way off topic, but I'd hate to see all the effort we already went to in keeping it clean go to waste.
_X_X_X_X_X_[small]Looks like I picked the wrong week to stop sniffing glue
DVD Rebuilder Guides: http://www.afterdawn.com/guides/archive/dvd_rebuilder_tutorial.cfm http://www.afterdawn.com/guides/archive/dvd_rebuilder_tutorial_advanced.cfm[/small]

 

So do you have any corrections? Or have you not been able to read it all without getting a headache?