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Old 08-11-2016, 12:28 PM   #1
RoamioJeff
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Need help in settling a debate

I have a TiVo Roamio with a Tuning Adaptor on a cable system that utilizes SDV. I believe I understand how SDV works.

I have a friend with a Roamio on a different provider (Comcast) who does not use a Tuning Adaptor. I do not believe Comcast implements SDV in his area (anywhere?).

My friend believes that the Comcast system somehow sends him certain linear cable channels using some sort of "on demand" mechanism based upon how many people on his "node" have requested the channel. He believes that certain channels are not present on his coax unless he tunes to them, and that his "node" manages bandwidth by adjusting the resolution based upon the channels that most people are tuned to.

I have never heard of this with a plain CableCard enabled device. Is Comcast doing this? I related to him that such a concept sounds like SDV, and if he is not using a Tuning Adaptor and SDV is not implemented by his provider, his CableCARD enabled Roamio is one-way. Also, there is no way for his provider to even know what channel he tunes to and that all of his available channels are present on his coax all the time.

So who is right? For Comcast is there some sort of virtual software Tuning Adaptor in the TiVo? Am I missing something?

p.s. This has nothing to do with content through the Comcast on demand app on a TiVo, only regular cable channels.

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Last edited by RoamioJeff; 08-11-2016 at 01:03 PM.
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Old 08-11-2016, 12:34 PM   #2
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What he described is SDV. And no you can't do SDV natively with CableCARD alone. You'd need an SDV Tuner Adapter to perform the upstream request for the channel to be tuned into, and it will also provide the frequency and channel within frequency to tune into for the TiVo unit.

To my knowledge no Comcast systems use SDV to date. I do know that many areas eliminated Analog channels (and provided a small adapter for those wanting what was the basic analog channels over digital) in order to free up those frequencies to get more digital channels in. Each analog channel required a full 6MHz frequency band, which they are now putting over 2-3 HD channels and 12-13 SD Channels before compression of MPEG2 - You can get a lot more when going to MPEG4 (H.264) which is what Comcast is moving towards. And I'm sure someone will chime in about how many Comcast are shoehorning in with both the move to MPEG4 and their overcompression (and their more recent compressing 1080i into 720p which results in poor quality than the 1080i which your TV or Cable box would deinterlace to 1080p directly instead of it being deinterlaced and the downres'd to 720p and then needing to be upres'd back to 1080p... on their more recent MPEG4 converted channels {I've seen as many as 8 720p MPEG4 channels on one frequency band - that could result in > 900 HD channels and eliminate all SD channels w/o even upgrading from 750MHz to 1GHz systems or going to say 450HD channels and 1500SD channels if they wanted, but need to back that off a bit for a few channels reserved for Cable Modem})

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Last edited by CCourtney; 08-11-2016 at 01:13 PM.
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Old 08-11-2016, 01:00 PM   #3
RoamioJeff
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Quote:
Originally Posted by CCourtney View Post
What he described is SDV. And no you can't do SDV natively with CableCARD alone. You'd need an SDV Tuner Adapter to perform the upstream request for the channel to be tuned into, and it will also provide the frequency and channel within frequency to tune into for the TiVo unit.

To my knowledge no Comcast systems use SDV to date.
Thanks for the confirmation regarding SDV on Comcast. My problem is that my friend is not an unintelligent guy and he is very confident about "something" Comcast is doing based upon what he's read on their web site, as well as his experience. It may be that the bandwidth/resolution management concept he is picking up on somewhere only applies to Comcast STBs.

So, does anyone else know of any existing mechanism outside of SDV where any of what I described can happen?

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Old 08-11-2016, 01:07 PM   #4
JoeKustra
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Originally Posted by RoamioJeff View Post
Thanks for the confirmation regarding SDV on Comcast. My problem is that my friend is not an unintelligent guy and he is very confident about "something" Comcast is doing based upon what he's read on their web site, as well as his experience. It may be that the bandwidth/resolution management concept he is picking up on somewhere only applies to Comcast STBs.

So, does anyone else know of any existing mechanism outside of SDV where any of what I described can happen?
First there is this: https://en.wikipedia.org/wiki/Switched_video

Also, with a satellite feed, on demand uses the internet to supply your content. This may be causing some confusion.

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Old 08-11-2016, 01:44 PM   #5
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First there is this: https://en.wikipedia.org/wiki/Switched_video

Also, with a satellite feed, on demand uses the internet to supply your content. This may be causing some confusion.
Thanks for that. I had forgotten the satellite method.

I think it's safe to say at this time that there is no 2-way communication between a TiVo and Comcast, outside of the on-demand app content.

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Old 08-11-2016, 09:18 PM   #6
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Originally Posted by RoamioJeff View Post
p.s. This has nothing to do with content through the Comcast on demand app on a TiVo, only regular cable channels.
ok, so I guess you know this part.. but just clarifying.. The On Demand content IS provided to you as a "regular TV channel". i.e. it is not streamed in the sense of something like Netflix, it is tuned via a normal channel... that happens to be set up when you started the On Demand session.

(The one thing I don't know about it is if this channel is ONLY authorized to you via CableCard, or if other people could tune to the same digital channel and watch -- similarly to how in the past people COULD tune to analog PPV channels and see what their neighbors had ordered for PPV -- possibly also involving descrambling.)

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Old 08-11-2016, 09:26 PM   #7
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ok, so I guess you know this part.. but just clarifying.. The On Demand content IS provided to you as a "regular TV channel". i.e. it is not streamed in the sense of something like Netflix, it is tuned via a normal channel... that happens to be set up when you started the On Demand session.

(The one thing I don't know about it is if this channel is ONLY authorized to you via CableCard, or if other people could tune to the same digital channel and watch -- similarly to how in the past people COULD tune to analog PPV channels and see what their neighbors had ordered for PPV -- possibly also involving descrambling.)
Thanks for the clarification ... that's the way I understood it also.

I was just trying to get clarification that the non On Demand channels were all present on the coax without any switching mechanism.

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Old 08-12-2016, 10:13 AM   #8
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Originally Posted by RoamioJeff View Post
Thanks for the clarification ... that's the way I understood it also.

I was just trying to get clarification that the non On Demand channels were all present on the coax without any switching mechanism.
OD from Comcast is not present on the Coax unless you order something, and then one channel is allocated to the OD you ordered, your cable card is tuned to that one ch. and you get your OD, each OD request is given its own ch. that only one cable card device can watch.

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Old 08-15-2016, 01:17 PM   #9
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Quote:
Originally Posted by CCourtney View Post
What he described is SDV. And no you can't do SDV natively with CableCARD alone. You'd need an SDV Tuner Adapter to perform the upstream request for the channel to be tuned into, and it will also provide the frequency and channel within frequency to tune into for the TiVo unit. To my knowledge no Comcast systems use SDV to date. I do know that many areas eliminated Analog channels (and provided a small adapter for those wanting what was the basic analog channels over digital) in order to free up those frequencies to get more digital channels in. Each analog channel required a full 6MHz frequency band, which they are now putting over 2-3 HD channels and 12-13 SD Channels before compression of MPEG2 - You can get a lot more when going to MPEG4 (H.264) which is what Comcast is moving towards. And I'm sure someone will chime in about how many Comcast are shoehorning in with both the move to MPEG4 and their overcompression (and their more recent compressing 1080i into 720p which results in poor quality than the 1080i which your TV or Cable box would deinterlace to 1080p directly instead of it being deinterlaced and the downres'd to 720p and then needing to be upres'd back to 1080p... on their more recent MPEG4 converted channels {I've seen as many as 8 720p MPEG4 channels on one frequency band - that could result in > 900 HD channels and eliminate all SD channels w/o even upgrading from 750MHz to 1GHz systems or going to say 450HD channels and 1500SD channels if they wanted, but need to back that off a bit for a few channels reserved for Cable Modem})
Hey, you talkin' to me?

To the debate, there is a way now that TiVo designed that's a software tuning adapter and I believe they tested and developed it with Comcast. If you go into the TiVo box diagnostics, towards the end in the TA section, have your friend check there and see if there's any values listed in the "SDV http" line or something similar (sorry I'm not near my TiVo). It is a way that TiVo developed for the TiVo to communicate with the cable co headend over the Internet and do the same thing that a hardware TA does, just through the interwebs. It requires the cable co to have equipment on their end though, so I haven't heard of any company doing it yet, but maybe Comcast is testing it in the friends market or something?

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Old 08-15-2016, 01:41 PM   #10
JoeKustra
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That line was added with 20.6.1 and it says:

Channel Sources:
Cs5: SdvHttp Inactive

It's after the tuners and before the cable card. Now I know what it means. Thanks.

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Old 08-15-2016, 05:49 PM   #11
RoamioJeff
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Thanks JoeKustra and HarperVision.

I called my friend and we went through the TiVo diagnostics screen and there is noting to in the cited entries to indicate that any software tuning adaptor functionality is in operation.

My friend is still still convinced that Comcast is using some sort of mechanism to "switch" video and dynamically control the resoution/bandwidth a channel consumes based upon the number of people watching it on a "node". I know of no known method used by any cable provider to do this with a one-way CableCARD device without SDV and a tuning adaptor.

So it will remain mere speculation until such a mechanism is identified.

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