HD SDI Capture Questions
 

I've read a lot of posts here about HD SDI aquisition and I have to admit I'm more than a little confused which is hard for a know-it-all like me to admit. I've read that HD SDI needs either a single SATA drive or an 8 drive SCSI array costing 30 G's. Hmmmm.... at least we all agree. Right now I live in the world of mere mortals. I have an Xl2 and use firewire, looks good, not great but it's rock solid and hassle free. I'm going to upgrade to the JVC HD100 or the XL H1 within the next few months, which one I choose is largely dependent on which format I can afford to support. I'd like to go Canon but if I can't afford storage it looks like the HD100. My idea was to take a gig-ethernet G4 put in a black magic card, SATA contoller, stack 4 drives and call it a day. Would this configuration work? I guess what I'm looking for is the cheapest/most reliable way to capture HD SDI. Any info would be of real help. Thanks, Jason.

Uh...don't know where you heard a single SATA drive can capture SDI, but if it could...I'd surely like to know about it.

BlackMagic Design has specs on their website, and they recommend an 8 drive (or more) SATA array. I've heard *rumors* of someone running a 6 drive Raptor system, but I don't have firsthand experience with it.
You'll need to download a test app to see throughput measured, but I can't imagine 4 drives of any sort being fast enough.

Here is another one of those situations where everybody assumes SDI has to be captured as uncompressed.

It does not.

SDI is just the port and transfer system which transfers as uncompressed to keep the quality at it's native format from the camera head.

In your system (depending on the system and codecs you have) you can capture to any video format you want to.

With a Decklink card on an Apple Final Cut Pro system you can capture to 10 bit uncompressed, 8 bit uncompressed, DVCPRO HD, Photo JPEG 25%, Bitjazz lossless 2:1 codec.

Capturing to the DVCPRO HD codec will work perfectly on even a single SATA drive only needing around 14 MB/S.

8 bit uncompressed and bitjazz should work fine on a 4 drive setup for awhile at least. The more the array fills up the slower they will get. With a 4 drive array you could get to about 50% full before you might start to drop frames. An 8 drive array will allow you to almost fill up the entire array.

Lacie makes an external 5 drive array (4 drives used for raid-0) that uses an external SATA II conection that will get 187 MB/S which is enough for awhile for 8 bit uncompressed.

Since it seems that all of the current HDV cameras only output 8 bit from component or SDI you would only need to capture 8 bit uncompressed anyways.


On the PC side of things sadly we are currently limited to uncompressed only from a Decklink card. Hopefully this will change someday.

Of course you are right, Thomas, but the assumption of uncompressed is there for a reason. Because it's always been that it's uncompressed until recent times. Additionally, the output from the cam is uncompressed, so it's somewhat abnormal to think of SDI as anything else.
Regarding the LaCie system, have you tested it? I ask because we've yet to get LaCie anything to work for any length of time, let alone sustaining datarate. Hollywood East made the mistake of purchasing several of their RAIDs for student use, and ended up shipping every one of them back.

re: HD-SDI capture to a single SATA drive
 

Yes certainly HD-SDI capture to a single drive would be compressed, and that is pretty much what the Wafian HR-1 (www.wafian.com) on-set recorder does with CineForm compression (www.cineform.com.) This device records to two SATA drives that are mirrored for data redundancy (so the speed of one drive is fine.) Prospect HD allows you to do the same, it even supports HD-SDI recording to a FireWire drive. The that theory CineForm is presenting is there are very few (if any) real-world examples that absolutely needs uncompressed (everything else in the workflow is compressed, D5, HDCAM, SR etc) as long as you have 'lite' compression at full raster (1920x1080 or 1280x720) and 10-bit, you pretty much have the same image as uncompressed, but on a much cheaper disk system. As there will always be doubters, the Wafian product will includes an uncompression mode for short takes, allowing users to learn for themselves that compression (when done well) is all good.

during summer i worked with 4 sata raid, 4x400Gb, with 10bit hdcam material. finalcut hd. decklink hd card. seagate disks. no problems.

i cannot remember exact frame rate, but this solution was more than enough (when tested with decklink speed check) to stand 10 bit hdsdi material.

when finished with editing/on line (~1h15' feature film) i started to "play" with it.
i captured more new hd materials just to feed the disks - to find so called "critical mass"

the problems started when disks are almost full. i cannot say exaclty at which moment this sarted, but i noticed that despite declink speed test results - which shows something like 28fps* 10bit 1920x1080 - the real "power" of disks were less then needed to work normally with hd.

during output to hd tape recorder (f500) it stoped sudenlly here and there with no regularity. the similar happened when film was played on hd monitor in full resolution. dropped frames etc...

so, my opinion is following - you can work with properly stripped sata raid which has at least 4 disks, (but not on PC!!!! - tested, just MAC), but need to leave certain space (10% ? , 15% ? for normal work)

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film was shooted on HD in PAL country, 25fps


filip