SDI Output - Portable Capture Device

[Hse Kha]

With the arrival of the Canon XL-H1 and other cameras with uncompressed SDI or component output, I am wondering if there is a portable capture device. Otherwise what is the point of this output, short of studio use?

My ideal device would be battery powered and consist of THREE 1.8 Inch Hard Drives (the same ones used in the iPod).

These three drives would be in RAID 5 configuration. So even if one hard drive failed, the footage would not be lost.

The current capacity of these hard drives is 60GB. So in RAID 5 you would get 120GB of capacity. However very soon 100GB 1.8 hard drives are coming, so then the capacity would be 200GB.

This device would have a circuit board that would take the SDI stream and in real time convert to a motion-jpeg based codec, like DVC-Pro or HDCAM, keeping the 4:2:2 color info. Something like 100-200 MBits/sec. The RAID 5 could handle this data rate easily.

So at 100 MBits/sec, 120GB would yield 163 mins and 200GB 271 mins.

The OEM cost of these three hard drives would be about $500. Add $200 for the circuitry and other material costs and add another $300 for profit.

So that is $1000 total.

Weight wise I estimate no more than 500 grams or 1 pound with the battery.

So is there (or will there be) such a device for $1000???

[Jonathan Houser]

Originally Posted by Hse Kha

With the arrival of the Canon XL-H1 and other cameras with uncompressed SDI or component output, I am wondering if there is a portable capture device. Otherwise what is the point of this output, short of studio use?

My ideal device would be battery powered and consist of THREE 1.8 Inch Hard Drives (the same ones used in the iPod).

These three drives would be in RAID 5 configuration. So even if one hard drive failed, the footage would not be lost.

The current capacity of these hard drives is 60GB. So in RAID 5 you would get 120GB of capacity. However very soon 100GB 1.8 hard drives are coming, so then the capacity would be 200GB.

This device would have a circuit board that would take the SDI stream and in real time convert to a motion-jpeg based codec, like DVC-Pro or HDCAM, keeping the 4:2:2 color info. Something like 100-200 MBits/sec. The RAID 5 could handle this data rate easily.

So at 100 MBits/sec, 120GB would yield 163 mins and 200GB 271 mins.

The OEM cost of these three hard drives would be about $500. Add $200 for the circuitry and other material costs and add another $300 for profit.

So that is $1000 total.

Weight wise I estimate no more than 500 grams or 1 pound with the battery.

So is there (or will there be) such a device for $1000???

Why would you compress an uncompressed signal? Motion-jpeg based codec, like DVC-Pro or HDCAM are all compressed formats. Are you trying to get around the HDV compression? Why not just get an HVX?

[Hse Kha]

Originally Posted by Jonathan Houser

Why would you compress an uncompressed signal? Motion-jpeg based codec, like DVC-Pro or HDCAM are all compressed formats. Are you trying to get around the HDV compression?

Because uncompressed data is HUGE and beyond protable means at present, and that high rate codecs are close to uncompressed anyway.

And HDV is poor for fast motion AND also 4:2:0.

So DVCPro or HDCAM are good compromises...

[Chris Hurd]

With no practical way to encode in an existing HD format, such as DVCPRO HD or HDCAM because those licenses are most likely unobtainable, you'd be looking at creating your own compression format, which would negate any hope of editing without creating a conversion application to go with it. So capturing uncompressed is probably the best way to go. But at nearly 1.5 gigabits per second uncompressed HD coming from the XL H1, even a 200GB RAID configuration would be extremely limited in usable recording time.

I can't do math on weekends... how much time would a 200GB disk array allow at 1.485Gbps?

[Hse Kha]

Originally Posted by Chris Hurd

how much time would a 200GB disk array allow at 1.485Gbps?

Firstly and sadly 200GB = 186.26GB - because greedy Hard Drive manufacurers use the definition of GB as a "billion bytes" and not 1024 to the power 3.

1.485 Gbits/sec = 0.185625 GB/sec (divide by 8 to get bytes from bits)

So now we divide the number of GBs 186.26GB by the rate of GB/sec to get the total number of seconds available:-

186.26 / 0.185625 = 1003.445 seconds or just 16 minutes and 43 seconds!

MOREOVER, I doubt a RAID 5 array of 1.8 inch drives can handle 1.485 Gbits/sec!

1.485 GBits/sec = 190MB/sec

Only a RAID-5 array of 10,000 rpm 3.5 inch drives could handle that - barely!

See this:-

http://sdd.toshiba.com/

The Toshiba 1.8 Inch Hard Drive 80GB, weighs only 62 grams and the power consumption is only 1.1 watts.

Sadly the Internal (i.e. REAL) data transfer rate is 164.3 - 341 Mbits/sec. This varies becuase the inner sectors transfer at less than half the speed of the outer sectors.

So assuming 164.3 MBits/sec = 20.5 MB/sec

Three drives in RAID 5 would get about double that. So we are looking at 40 MB/sec or 320Mbits/sec - fine for HDCAM, DVCPro, etc, but NO WAY for uncompressed!

[Hse Kha]

I did some more math and came up with the uncompressed output as 711 Kbits/sec about half of the 1.485 Gbits/sec that Canon claims. So what am I doing wrong?

The resolution is 1440x1080. So each frame has 1,555,200 pixels or for fields it is 1440x540 and 777,600 pixels.

No multiply the number of pixels in a frame by 29.97 or the number of pixeld in a field by 59.94 and you get 46,609,344 pixels per second.

Now with the color space of 4:2:2 each pixel takes 16 bits of data. So multiply 46,609,344 by 16 and you get 745,749,504 bits of data per second or 711 Kilo Bits per second (divide by 1024).

[Hse Kha]

More thoughts on uncompressed capture:-

If my math is correct then the data rate for uncompressed capture is about 700 Mbits/sec.

If one was to use a lossless codec (like huffy), that could come down to 300-400 Mbits/sec.

So then you could get an hour of video on 200GBs and it would be uncompressed. The data rate would still be out of reach for an 1.8 inch hard drive array. BUT it would be well in reach of a 7200rpm 3.5 inch hard drive array and also possibly an array of 2.5 inch hard drives as used by notebook computers...

[Kevin Shaw]

Remember that HD-SDI data is full 1920x1080 resolution, so that's 2,073,600 pixels per frame x 29.97 fps = 62,145,792 pixels per second, times 24 bits/pixel = 1,491,499,008 bits per second or 186 MB/sec. The latest SATA II RAID controllers are delivering write speeds well in excess of that amount, for example as shown in these 3Ware benchmarks: http://www.3ware.com/products/benchmarks_sata2.asp.

On Pricewatch.com, good 400GB SATA hard drives are selling for $207 each, or $1656 for 3200GB of pre-formatted capacity. Round that down to maybe 3100GB after formatting and you've got ~3,100,000 MB of capacity, or enough to capture about 4.6 hours of full uncompressed 8-bit 4:2:2 video. Add the basic components for a computer plus a good RAID controller and an HD-SDI capture card, and you've got that much uncompressed capacity for under $5000 if you're frugal about it. Compare that to Cineform proposing to ask $15K for ~14 hours of ProspectHD recording in the form of the Wafien drive, and the cost of these two options is comparable per hour of recording time. Of course you could build your own ProspectHD capture setup for a lot less, and few people really need to work with uncompressed HD, but at least you've got some choices.

Now the question becomes, what's your definition of portable? If you could capture several hours of ProspectHD or uncompressed video in a computer costing a few thousand dollars and powered by a portable AC generator, would that work? If not, your best bet may be to consider the Panasonic HVX200 with the external Firestore hard drive due out next March.

[Keith Wakeham]

single link hd-sdi like on the xl hd1 is actually 2 channels @ 1920*1080 at almost any frame rate (24p has 2750 samples per line, 1920 active, 25 has 2650 but still only 1920 active and 30p has 2200 but still only 1920 active). These channels are 10 bit each. So your datarate for 1080 @ 30p is 148 MB/s.

I'd be very surprised if the 1.8" toshibas can handle 160mbits because even the faster drives like hitachi 7k60 2.5" drives have the slowest speed being around 20Mbyte/s which is only 160mbit (see http://www.xbitlabs.com/articles/sto...5-7200_10.html)

Likely that number that is listed on their website is the maximum theoretical performance that cannot be achieved in real world situations. So your looking at about 8 - 10 of these drives to do a hd-sdi capture at least (uncompressed). The only data rate that really matters is the slowest if you want to use the entire disk.

[Kevin Shaw]

Originally Posted by Keith Wakeham

Likely that number that is listed on their website is the maximum theoretical performance that cannot be achieved in real world situations. So your looking at about 8 - 10 of these drives to do a hd-sdi capture at least (uncompressed).

My point was that you can build a computer with an HD-SDI capture card and a fast 8-drive RAID array holding several terabytes of data for a few thousand dollars, and that's something you could easily carry in a car (or even a golf cart) along with a portable power source. And even assuming the 3Ware benchmarks are generous, they've got overhead of almost 100% compared to uncompressed HD data rates in an 8-drive configuration. Plus data rate drop-off on modern hard drives is typically not very significant across at least 75-80% of the drive, so you wouldn't lose a huge amount of capacity to that consideration. And lastly, given the option of capturing instead to something like ProspectHD or Avid DNxHD, concerns about drive performance would be irrelevant for a full computer-based setup.

So the only practical problem here is having an HD recording solution which is truly portable, in the sense that you don't have to be plugged into an AC power source to use it. So far it looks like Panasonic has the lock on that for high-bandwidth recording, and it's a simple matter now to record HDV on the run to either tape or drive based options.

[Peter Ferling]

There has to be a line drawn here. That is, when you have so much gear along for the ride, that you might as well just rent a high rez HD camera with decent glass, and a small crew to wrangle the cart and cable along.

The H1 will provide a balance of 4:2:2 SDI in studio or location shoots, but for run and gun, you'll have to see how nicely the HDV material will cut in, (never mind the compressed audio, that is whole other issue).

Bottom line, we've now defined how consumerish these HDV camera's are.

[Brian Longley]

Greetings all; just back from the my training session on the XL H1. I have read the post and reply, but a proper hard drive for the SDI or HDI output of the camera is going to need to be considerably more powerful if you want uncompressed video. Since the uncompressed signal on the H1 is 1.5 gigabit, a hard drive recorder will need to either compress the signal, or have enough data throughput to handle either SDI at 8 bit uncompressed, or 10 bit, or if possible, the 8 or 10 bit HDI signal. This is a complicated process to connect the drives, the controller, and the video input device. This will be a work in progress. There is a device coming soon that offers compression, and I have asked several companies that make similar products, and I await reply. I will be posting information as I have it.

thanks brian, http://www.zotzdigital.com

[Jonathan Lutz]

So how do the big boys do it? Scott Billups captures 4:4:4 progressive HD from a Viper right into his G5 with a Blackmagic DeckLink HD Pro card. Judging from the picture here (http://www.blackmagic-design.com/cas...istorychannel/) it looks like he's got HUGE Systems' 4Gbit MediaVault 4105 (http://www.hugesystems.com/Products/) that can handle 300MB/sec dual, and it's only $3,600. His system looks pretty portable to me.
Granted, you're not going to run through the woods with it, but that's what Firestore's FS-4 HD is for.

[Keith Wakeham]

Their already is some uncompressed hd-sdi solutions available. Some russian company says they have a flash based one at ctt.ru and their are definetly some other things in the works. When The XL HD1 gets out i suspect their will be products available shortly after that will do some amazing quality either uncompressed or lightly compressed and actually be portable.

[Brian Longley]

sorry, didn't get an email that there were follow ups;
Everthing here is a matter of capture with, or without, compression. Uncompressed with Viper, but we are talking about a portable battery powered field unit for capturing these signals, which is where the compromise has to come in, at least for now. the Firestore and other devices for as much data as there is in and SDI or HDI type signal, and the various levels of HD, will require multiple DC powered drives to make this work,

a 4 gig fibre channel, dual 5 drive (4105) from Huge will be fine for capture of an HD signal even in 4:4:4, it is right up to the edge of what a 5 drive can do though and still leave you enough headroom to view other things in real time, without rendering. Overkill is not a fair description of what you get when you have more drive speed and space than required. That means ease of use, extreme speed. A Huge 4 gig fibre, 10 drive model, (4210) would likely do 12, maybe 14 real time streams of SDI video. Their 320R SCSI would do 6 or more (all on a Mac G5 mind you, 4-8 gigs RAM) But HD is demanding when you are talking about a 1.5 gigabit stream coming from the new XL H1. that is 187.50 megabytes per second sustained data requirement, in 4:2:2. If you want real 1080i, you have it. no questions, hands down, no compression, no BS. This is why 4 gigabit, raid 3 (at least) dual channel, and 10 drives at least, will make 500/600 megabytes/second sustained/burst data rates. This gives you a real time stream or two with your effects. You don't have to render everything, the effect won't hitch in preview, etc. but most important, it allows you to work with the best stream of video that most people can afford. 1080i uncompressed HD is pretty powerful. Check the Sony CineAlta and Panasonic Varicams and what you will spend on one of them. Check their output spec for video at 4:4:4 and 4:2:2. Figure 80K on up, no deck.
Headroom is not overkill, it is that extra speed to keep you running free of issues. it's nice not to have issues. This is why it is better to work with a G-Technology Graid, two drive raid, than a single external firewire drive on a laptop, same thing with SCSI, it is fast, but not as fast as the fibre, on up to the very fastest fibre systems. The more headroom, you get more speed and stability as you edit, more stability when you capture. Remember, if you are renting a deck at $2000 a day to capture to, and have a deadline, budget, etc... the last thing you need is a problem.

but back to DC powered drives;
I hope it soon, but it could a while before someone makes a DC powered hard drive set that can handle at least uncompressed SDI in the field. HD may take a while. Compression is everything. The pocket drives used for the firestore and laptops are perfect, they need a backplane like the Medea and Huge Systems have to give it this speed of data transfer
Since I last posted, I have also asked G-Technology, AJA, and Medea if they would consider this type of small drive array that will allow us to capture uncompressed for about 3 hours, at least and at minimum, downconvert HD to SDI for 10 bit capture (8 will be acceptable, but oh, when we can do real HD!) that would be like having DVCPRO50 in an XL H1, as the image capture quailty would be greater resolution at 1080i, but compared to a very good camera indeed that has larger chips and a very good Canon Broadcast lens, it's 40K price tag may not be worth the difference of a Canon XL H1 down res'd to it's capture level. A complete XL 1H kit is affordable, and really blurs the lines between the higher priced cameras for a lot of videographers. It is worth seeing. It is a considerable difference in cost, the difference in picture, is yet to be seen. Give it a couple weeks now.


the great part is, connect an AC cable to these daytime DC drives at the end of the day to your G5 (or even another type of computer) and start editing the way you can do with a firestore. It may become the field shooters only drive set required. Hope we see this option real soon. brian