Is my understanding of QAM, DTV and HDTV correct?

[blade]

I've spent the last few days reading up on QAM, DTV, and HDTV. I think I'm starting to understand it all. I would appreciate it if someone would read over my comments and let me know if I'm understanding everything correctly.

I currently have Comcast's total preferred analog service. My understanding is I can receive (legally) any unencrypted DTV and HDTV content comcast transmits by using a QAM capable device without upgrading to digital cable (despite what the cable company leads me to believe).

There are QAM capable tuners for PC's but they only work with their own software which makes them useless for Sage. Is this correct?

Currently the only option for capturing HDTV from cable in Sage is through firewire and using a STB.

[stanger89]

Sounds about right.

[blade]

Thanks, just wanted to make sure I was on track before shelling out any cash.

[parkimar]

Thank you, nice and simple.

Im about to move to the US, and need to start figuring this out.

Cheers

Mark

[salsbst]

I'm reusing this thread because I'm hoping to rid the QAM-product-specific threads of future noise relating to general questions about QAM. I'm hoping that we can make this the thread to talk about QAM, and keep the others focused on the particular products.... we'll see.

Here's my QAM situation and understanding of the variables... just as a data point and point from which to start discussion. There are others on this board that know more than me about the subject, so I'm anticipating and hoping for clarifications/corrections.

My cable box states that no channel that reports as 5c-enabled. I can record almost all channels on the cable box via Firewire. There are two exceptions: the CBS and ABC HD locals. The reason I can't record those two is that they are flagged (in the MPEG2 stream) as CCI=1 (copy once). This is different than 5c. With QAM PC cards, I can record all of the locals and a few stray/odd other channels, including a couple that I don't receive at all in my cable box. These are the channels that are not encrypted.

So, there are really 4 variables that I can think of when determining whether you can record a cable channel to PC:

1) Is the channel encrypted? If so, a cable box is your only option.
2) Is the originator (broadcast network) flagging the MPEG2 stream as CCI=1 or CCI=2? Or is the cable company (re)encoding it that way? If so, a PC card is your only option.
3) Is the channel or your entire cable box set to 5C=copy once or copy never? In this case, I *think* the MPEG2 stream is encrypted anyway, and therefore you have no chance to record to PC.
4) Is there something peculiar about the QAM modulation that throws some/all PC cards (or other retail QAM capture devices such as the OnAir GT)?

[lobosrul]

I believe 5C encryption and the copy once flag are linked. With the copy once flag, the device (cable box) will only output to "trusted" devices.

In my area Comcast has flagged ESPN2HD, MHD, and HBOHD (and I assume the other premium channels), along with a few, mostly irrelevant (to me) digital SD chans. All locals, and most other channels are in the clear. Strangely ESPN is in the clear but ESPN2 is not. Im suprised your local chans are set to copy once.

As far as QAM goes, its fairly uselss if you have an OTA HD tuner, and are in range. Last I checked, all I got thru QAM was the locals that Comcast has available in HD (and due to contract disputes they dont carry the CBS and CW affiliates) . I also got what other people were watching on demand! I saw several ppl watching "late night" programming

[stanger89]

Originally Posted by salsbst

My cable box states that no channel that reports as 5c-enabled. I can record almost all channels on the cable box via Firewire.

You're lucky, don't tell anyone

There are two exceptions: the CBS and ABC HD locals. The reason I can't record those two is that they are flagged (in the MPEG2 stream) as CCI=1 (copy once). This is different than 5c.

Yes and no. In the most technical sense, yes, it's not 5c. DTCP, the official name of 5c (5c comes from the 5companies that created DTCP) is the encryption/authentication protocol for firewire that allows recording of protected content.

The CCI flag is not directly DTCP, but if it is not "copy freely" will require a DTCP connection/output in order to allow recording. This is what most people mean when they say a channel/show is 5C=1, that the show if flagged such that DTCP is required for recording.

3) Is the channel or your entire cable box set to 5C=copy once or copy never? In this case, I *think* the MPEG2 stream is encrypted anyway, and therefore you have no chance to record to PC.

Probably not necessarilly, it should be perfectly possible to have something unencrypted but with CCI!=Copy Freely, this is basically what the broadcast flag would have been. Your locals appear to be like this.

Of course in reality, almost everything is encrypted that has CCI!=Copy Freely.

4) Is there something peculiar about the QAM modulation that throws some/all PC cards (or other retail QAM capture devices such as the OnAir GT)?

QAM 256, the form used by most cable, requires tight tolerances on reception and a good chunk of memory on the demodulator (I think that's right), such that it's quite tricky to do right. Fortunately most cards handle it well now.

Of course providers are known to do peculiar things with how they encode the transport streams as well.

[salsbst]

I'm certainly not complaining about my firewire situation.

stanger, did you notice that I removed my location from my profile?

[salsbst]

I specifically revived this thread to generically discuss QAM, because the generic QAM discussion was polluting the threads about the specific products. Never again...

Edit: AutumnWave OnAir GT product discussion posts were moved here. - Opus4

[Diginerd]

Sorry I posted over here as I thought you were directing me to it!! oopsy..

QAM in general (Trying to get back on topic) from Cablevision in CT seams to be a pretty friendly place, and is definately worthwhile persuing with what ever tech you see fit. The toys I bought do the job handling QAM in Sage, from SD to HDTV, and that's a huge step, and something I have been wating for for a long time.

Here's what I get off the wire (Excluding the analog stuff which has the same availability with pracically any capture device.)

As you can see from the list there is a fair amount of simulcasting. for example ABC is is available on the wire as analog, QAM 544x480, 720i and 1080i...


82-4 640x480 Home Shopping Network
82-5 640 x 480 QVC
90-3 80s radio
823 80s RADIO
92.1 704x480 WLIW21
92.2 704 x 480 WLIW Create
92-3 16:9 704x480 ABC7
92-4 ABC 1280 x 720 HD
92-5 ACB7 528x480 News accuweather
94-1 544 x 480 CBS (Letterman)
94-2 544x480 NBC4
94-3 640 x 480 Fox 5
94-4 abc (news?) 640 x 480
94-5 espn 640 x 480
94-6 cw11 640 x 480
94-7 thirteen 640x480
94-8 640 x 480 WLIW21
94-9 hispanic u41
94-10 640 x 480 ????
99-1 HD CW11 1920 x 1080
99-2 the tube 704 x 480
99-3 HD espn 1280x720
101-1 NBC 4 weather + 640 x 480
101-2 480 x 480 ??
101-3 HD NBC4HD 1920 x 1080
101-4 HD Fox 5 1280 x 720
104-1 league pass advert 528 x 480
106-2 radio 544x480 green screen (Claasic?)
106-3 radio 544x480 green screen (Jazz?)
109-1 city classics (nyctv) 640x480
109-2 hispanic 544x480
109-3 640 x 480 ??
109-4 hispanic 640x480 (Triangle in triangle logo)
109-5 WLNY (was showin inside edition at 23:47)
109-6 cbs 704 x 480
109-7 abc news 704x480
109-8 704 x 480 ??
109-9 704 x 480 NBC
109-10 704 x 480 (Showing Will & grace @23:50)
113-1 shop nbc 704x480
117-3 704x480 news 12 Connecticut
118-1 thirteen HD 1920 x 1080
118-2 ei (Kidz 13) 704 x 480
118-3 thirteen world 740x480
118-4 CBS HD 1920x1080

There are a fair few channels that my toy (Trying not to name products again) can't get, as I believe they are indeed flagged, and require an STB to get at them.