Registered: Nov 2001
Location: St Louis MO USA
Posts: 0

I've been reading posts about HDTivo, and I keep seeing statements that capacity is a big issue.

With a DirecTivo, you get roughly an hour per gig of space. A 480p signal has roughly 2-3 times the information of a standard signal (correct? DSS ~ 400i?). So, given that there's very little on DSS in HD anyway, it seems like even with a 60 gig drive you'd be able to get 10 hours of HD (480p) and another 30 hours of standard def. Even 1080i shouldn't be much more than 2-3 times the 480p requirements -- giving you plenty of room to grab a couple 1080i movies and too much regular tv to watch in a week anyway.

My actual question is, does anybody have hard numbers for storage requirements of the [popular] HD formats?

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Registered: Apr 2000
Location: Carson City, Nevada
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1080i requires about 18Mbps, which means with the DirecTiVos current 40GB drive it would only be able to hold about 5 hours. 720p requires about 16Mbps, which would mean about 6 hours on the current hardware.

Dan

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Registered: Oct 2000
Location: glen ridge, nj, usa
Posts: 745

A year or so ago, HDTivo was just too expensive to consider.

Now you can get 120G drives for less than $200 in bulk. This means a 30 hour HDTivo with 2 120G hard drive could be built for about $1000-$2000.

The problem is not the price anymore. Its just the demand. The demand for HDTV just doesn't yet offset the startup costs in such a product. Until enough people clamor for it, Tivo won't build it.

Almost certainly NOT in 2002. MAYBE in 2003, but it will probably be DTivo not a SA. (or even cooler a DTivo with a antenna ATSC tuner installed!). Just my prediction since the demand for HDTV will be higher among DirecTV customers than it will be for the rest of the country.

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Registered: Mar 2000
Location: Valencia, Ca
Posts: 221

Clamor! Clamor! Clamor!

I think the satellite industry needs to take a good, hard look at high definition right away while there's discussion of merging and swapping out IRDs. New receivers should be able to take a high definition signal and downcovert it to standard definition. This should be standard for all receivers, and not some pricey high end option. It's just a bigger MPEG-2 stream, playing it back and downconverting it really isn't such a big deal these days with modern decoders, especially when you consider that some sort of an mpeg decoder is necessary for a DSS receiver anyway.

If they did this, they wouldn't need to duplicate every HDTV channel with a SDTV equivalent. EVERYONE would be able to enjoy the better quality pictures HDTV offers. Some would see "Better-than-DVD" downconverted video, while others with the more expensive sets and IRDs could see full blown high definition.

30 hours of HDTV quality video is more than sufficient. Don't forget that a 30 hour standalone is 30 hours at basic quality, most people use Medium or High giving them 18 or 14hours. It's not likely to be filled with 100% high definition for a long time to come anyway.

-- Rob

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Registered: Oct 2000
Location: glen ridge, nj, usa
Posts: 745

There is an even more compelling reason for a combined E*/D* to support ATSC in all receivers: save precious bandwidth!

Currently DirecTV broadcasts HBO in both a 15Mbs HDTV signal AND a 2-3Mbs STDV signal. Why bother! By adding ATSC support in IRDs, you can save bandwidth. Maybe even squeeze those HDTV channels up the max of 18Mbs instead of leaving them at 15Mbs. (DirectTV gets about 30Mbs a transponder. HBO and HDNet share on feed and get a 15Mbs average signal).


Of course this may be the future anyways. What happens in 2006 (or whenever they actually do this) when networks stop broadcasting in NTSC. Woudln't DirecTV want to be able to pass through the native ATSC signal from the channel provider. Especially when the bandwidth is the same as the current dedicated satellite bandwidth. Currently differences in the encoding formats prevent this entirely.

This will be important as more and more broadcasters are using pre-encoded MPEG2 streams. DirecTV signals use MPEG2 signals that are encoded real-time. But real-time algorithms are plauged with pixelation errors. Pre-encoded MPEG2 streams can look fantastic. Just look at a DVD movie compared to a standard DTV channel. DVDs are usally free of most pixallation errors whereby DTV is not. They both use about the same amount of average MPEG2 bandwidth.

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Registered: Nov 2001
Location: Playa Del Rey (LA), CA
Posts: 89

Price even for HDTV decoding will be way down later this year. Philips has announced a chip that can take care of all the standard formats for HDTV decoding, and convert it to any standard output (1080i, 720p, 480p, etc.). Once this shows up in cards, boxes, etc., I would expect HDTV decoders and anything that wants to be HDTV will be a heck of a lot cheaper.
Prices for the chip are estimated to be $50 or less in quantities.

Cheap decoder chips + cheap disk drives = reasonably priced HDTV PVR!

Christmas this year should be fun.....

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Registered: Nov 2001
Location: San Diego, CA
Posts: 32

Everyone is missing the fundamental problem with doing HD on a PVR.

The hard disk.

Not IDE. IDE can handle it. The hard disk cannot.

Hard disks can only really handle a sustained bit rate of around 10MBps, 80Mbps. Lets say you are recording 2 HD shows and playing one back. Given that you should probably design worst case, which means HD = 19.4Mbps (2.425MBps), that's a bandwidth of 7.275MBps. Now you hit Rewind. Bam! There goes your bandwidth. Even with dropping frames, you still have to pull the data off the disk to extract the part you want to display. And you want to stay efficient (efficient for the hard disk = 512byte accesses). Then there's the picture quality. About 4fps in trick play. Yuk!

HD and PVR is a ways off.

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Registered: Jan 2001
Location: Sunnyvale, CA, USA
Posts: 420

First,

I believe the approximate bit rates for various resolutions 'post-compression' are:
1080i60 - 16x9 - 18.8 Mb/s
1080p30 - 16x9 - 18.8 Mb/s
720p60 - 16x9 - 16.9 Mb/s
1080p24 - 16x9 - 15 Mb/s
720p30 - 16x9 - 10.2 Mb/s
720p24 - 16x9 - 8.1 Mb/s
480p60 - 16x9 - 8 Mb/s
480p60 - 4x3 - 8 Mb/s
480i60 - 16x9 - 5 Mb/s
480i60 - 4x3 - 5 Mb/s
480p30 - 16x9 - 4.5 Mb/s
480p30 - 4x3 - 4.5 Mb/s
480p24 - 16x9 - 3.6 Mb/s
480p24 - 4x3 - 3.6 Mb/s

Did you expect any less from me?

quote:

---

Originally posted by mishagray
Of course this may be the future anyways. What happens in 2006 (or whenever they actually do this) when networks stop broadcasting in NTSC. Woudln't DirecTV want to be able to pass through the native ATSC signal from the channel provider. Especially when the bandwidth is the same as the current dedicated satellite bandwidth. Currently differences in the encoding formats prevent this entirely.

This will be important as more and more broadcasters are using pre-encoded MPEG2 streams. DirecTV signals use MPEG2 signals that are encoded real-time. But real-time algorithms are plauged with pixelation errors. Pre-encoded MPEG2 streams can look fantastic. Just look at a DVD movie compared to a standard DTV channel. DVDs are usally free of most pixallation errors whereby DTV is not. They both use about the same amount of average MPEG2 bandwidth.

---

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Registered: Apr 2000
Location: Richmond, CA
Posts: 31

There are no technical problems with doing an HD PVR, and I don't think TiVo or anyone else in the DVR game has ever really claimed there was. The Dish HD DVR demonstrated at CES this year will do dual HD recording (from satelllite) while watching a prerecorded HD program. From Ramsay's response at the press conference at CES, he made it sound very much that HD was not a technical issue but rather a business issue. When you have finite resources, you have to decide where will you get the most bang for your buck - and so far it hasn't been with an HD DVR.

However, we won't have much longer to wait. This year a number of people will have HD DVRs connected to their TVs. Who makes them though is the big question.

--Andrew

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Registered: Nov 2001
Location: San Diego, CA
Posts: 32

quote:

---

Originally posted by Bilbrey

I believe the approximate bit rates for various resolutions 'post-compression' are:

1080i60 - 16x9 - 18.8 Mb/s
1080p30 - 16x9 - 18.8 Mb/s
720p60 - 16x9 - 16.9 Mb/s
1080p24 - 16x9 - 15 Mb/s
720p30 - 16x9 - 10.2 Mb/s
720p24 - 16x9 - 8.1 Mb/s
480p60 - 16x9 - 8 Mb/s
480p60 - 4x3 - 8 Mb/s
480i60 - 16x9 - 5 Mb/s
480i60 - 4x3 - 5 Mb/s
480p30 - 16x9 - 4.5 Mb/s
480p30 - 4x3 - 4.5 Mb/s
480p24 - 16x9 - 3.6 Mb/s
480p24 - 4x3 - 3.6 Mb/s

---

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Registered: Jan 2001
Location: Sunnyvale, CA, USA
Posts: 420

quote:

---

Originally posted by pauly666
These aren't transport stream bit rates - they're video bit rates. Aren't TiVo's recording transport stream?

---

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Brett - The Happy Lab Rat

Experience is the one thing you get, right after you need it.

TiVo doesn't make the content, TiVo makes the content better.
That's my opinion, and I strongly agree with it.

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Registered: Nov 2001
Location: San Diego, CA
Posts: 32

quote:

---

Originally posted by Bilbrey

In the case of the current TiVo's, they record 'SD' signals where the 'video bit rate' and the 'transport stream bit rate' is essentially the same. In DTV transmission, you can extract the given 'video bit rate signal' from the transport stream. Meaning that one DTV transport stream can handle multiple embedded signals.

---

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Registered: Jan 2001
Location: Garden City, MI, USA
Posts: 29

quote:

---

Originally posted by pauly666
Everyone is missing the fundamental problem with doing HD on a PVR.

The hard disk.

[snip]

HD and PVR is a ways off.

---

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Registered: Apr 1999
Location:
Posts: 268

quote:

---

Originally posted by pauly666
Hard disks can only really handle a sustained bit rate of around 10MBps, 80Mbps. Lets say you are recording 2 HD shows and playing one back. Given that you should probably design worst case, which means HD = 19.4Mbps (2.425MBps), that's a bandwidth of 7.275MBps. Now you hit Rewind. Bam! There goes your bandwidth

HD and PVR is a ways off.

---

Except that bandwidth requirements don't change when you hit Rewind. You are still only juggling three streams. Two recording and one playback. So, you are only using 72% of the available sustained transfer rate, using your numbers.

quote:

---

TiVo could build a SA HD unit and be ok bandwidth-wise.

---

I thought you just finished arguing to the contrary.

quote:

---

If they wanted to build a dual tuner DTiVo, and if DirecTV does not control the HD formats, they're gonna be in trouble until hard disk manufacturers can actually make use of the IDE bus properly.

---

HD channels on DirecTV are using a 15Mbs stream. Juggling three of these streams is nearly a non-issue.

/jab

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Registered: Jan 2001
Location: Sunnyvale, CA, USA
Posts: 420

HD encoder!!!

quote:

---

Originally posted by controlio
The TECHNOLOGY is not the issue here.

[snip]

So to make a long story short, it ain't the hard drive's fault.

---

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Brett - The Happy Lab Rat

Experience is the one thing you get, right after you need it.

TiVo doesn't make the content, TiVo makes the content better.
That's my opinion, and I strongly agree with it.

Last edited by Bilbrey on 01-30-2002 at 06:42 AM

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Registered: Mar 2001
Location: Arden Hills, MN USA
Posts: 45

Pauly666 wrote:

quote:

---

Hard disks can only really handle a sustained bit rate of around 10MBps, 80Mbps.

---

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Registered: Apr 1999
Location:
Posts: 268

Bilbrey,

Why would one need an MPEG encoder for OTA HD recording? Why not simply grab the bit stream? There are already PC-based products that do this.

/jab

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Registered: Jan 2001
Location: Sunnyvale, CA, USA
Posts: 420

quote:

---

Originally posted by JAB
Bilbrey,

Why would one need an MPEG encoder for OTA HD recording? Why not simply grab the bit stream? There are already PC-based products that do this.

/jab

---

__________________
Brett - The Happy Lab Rat

Experience is the one thing you get, right after you need it.

TiVo doesn't make the content, TiVo makes the content better.
That's my opinion, and I strongly agree with it.

Last edited by Bilbrey on 01-30-2002 at 06:45 AM

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Registered: Aug 2000
Location: Burnsville, MN, USA
Posts: 242

quote:

---

Originally posted by pauly666
...they're gonna be in trouble until hard disk manufacturers can actually make use of the IDE bus properly.

---

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Registered: Nov 2001
Location: San Diego, CA
Posts: 32

NO PEOPLE!!!

When you hit rewind (or any trick play case, except pause), you have to bring more video off the hard disk faster! You either jump around on the hard disk, slowing down data retrieval from the disk, or you bring data off the disk and jump around in local memory, picking the frames you want to display. In actuallity you probably have to do some of both, since you want to be efficient with the hard disk and pull data off in sectors.

Some quick/dirty calcs:
Input = IBBP, sequence of 15 pictures, 20Mbps HD or 2.5MBps (easier math!), 30fps, sequence size = 2.5/(30/15) = 1.25MBps
Trick play, 15x rewind at 4fps (yuk!), data rate = 4*1.25MBps, or 5MBps!!!

That's your playback channel... yes it's worst case, but all good designs should be worst case! And 4fps... ewwww!

JAB - I was making the distinction with the SA HD TiVo because it only has one tuner... therefore doesn't have such a high bandwidth requirement for storage.

panictivo - yes, the data makes the Maxtor sound fast, but that's just a small portion of the disk!! It almost grinds to a halt in other areas - thats why they have buffer ram in there, in a vain attempt to provide a somewhat constant bit rate.

Syzygy - I was referring to the fact that although the IDE bus supports plenty fast bit rates, hard disks can't even come close to using it continuously. Burst - maybe. Continuous... not even close.

controlio makes a good point about RAID though... but given the most expensive part of the PVR is already the hard disk, I would think there would be some considerable resistance to increasing the cost in this area...

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