What exactly does HD-SDI give you?

T

TheMusician

Well-known member
I am wanting to upgrade my sony hc1 to a prosumer grade camera. I love the idea of the HVX200 because of its 4:2:2 capabilities, but it does not have the low light capabilities for my needs. I also really like the XH A1, but I am not a big fan of HDV. I understand that you can get an XH G1 and record via HD-SDI to a hard drive at 4:2:2. That sounds very attractive to me, but both my local Canon dealer and Canon technical support could not answer simple questions that I have, so I look to you for the answers.

1)I know that HD-SDI is more of a RAW format, but is it a format that can be loaded into Vegas or Premier Pro for editing? Is it an .AVI, .MOV, what exactly is the format of HD-SDI?

2) Has anybody ever compared the footage between Canon's HDV and HD-SDI? are the colors more rich, less artifacts in the video, or is there very little difference?

Thanks for any insight.
 
HD-SDI is not a "format", it's a digital signal transfer protocol. You'd have to "capture" the HD-SDI signal into a format on your computer. That could be uncompressed, or it could be compressed into an existing codec. It could be saved as individual frames or as a .MOV or as an .AVI, it all depends on your HD-SDI capture board's capabilities.

Barlow Elton has posted some comparisons of analog component vs. HDV, and I think he may have posted some HD-SDI vs. HDV. There are differences, yes. HD-SDI or analog component is better, yes. But it's very close, and you'd have to face the fact that working with uncompressed HD-SDI capture is extraordinarily space-inefficient and very, very taxing on your system; you'd need probably a five-drive RAID to work with the footage. In other words, it's totally not practical for most circumstances.

Newer cameras are offering HDMI output, and BlackMagic offers an HDMI capture board. HDMI is also a digital HD uncompressed signal transfer protocol; think of it as the "poor man's HD-SDI". (but that's an unfair characterization; HDMI can probably deliver a signal every bit as good as HD-SDI, but the hardware and cabling are sooooooooo much cheaper for HDMI!)

Either way, it's simply not practical or viable to work with uncompressed HD to any large degree on today's computer systems.
 
Hi Musician,

Barry's info is spot on, but I guess I would add a few wrinkles based on my experience with HD SDI.

It's true that it's not practical in most situations to capture uncompressed HD-SDI, which flows at a 1.45 Gbps bit rate. This translates to well over 100 megaBYTES per second, which is obviously enormous. Just to give some perspective to that--full DVCPRO HD 60p or 1080i requires about 14 MBs, and HDV is a mere 3.5 MBs.

IMO, what HD SDI offers is a way to bypass HDV and choose a milder form of compression, rather than attempting true uncompressed. There are several codecs, including DVCPRO HD that can be captured to that will give you excellent quality. I get uncompressed quality with a lossless QT codec I purchased as an add-on to FCP called Sheer Video, and it's about 1/3 the data rate. It simply packs the bits more efficiently, but mathematically retains every last drop of image information. This can be captured to and edited from with a simple 2 drive SATA raid.

Now, the bigger question is how much hassle would you be willing to put up with in order to achieve technically better quality (spec wise) than HDV offers? As of right now, there are no HD SDI firestores that can be attached to a camera rig and allow the operator to record untethered. My own use of HD SDI requires capturing a live camera signal from the XL-H1 directly into a FCP capture window. This means I have to run a BNC cable from the camera and hit record on the computer before any single take.

Obviously, with a capture technician this could work fine in greenscreen/studio situations and maybe even on suitably budgeted productions with a dedicated "video village", but for the single "run and gun" shooter--it just ain't happenin'.

I think when we see a laptop HDMI or HD SDI capture card, we could be talking about semi-practical SDI field acquisition...but even that would be a PITA for a single operator. For most it's simply firestore-style dedicated devices or just go with the on board recording provided with HDV.

Needless to say, for most it's still HDV, but HD SDI does offer a compelling alternative if your needs are greater than the qualtiy that can be achieved with HDV.
 
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Thanks for the info guys. It now makes total sense to me - your final format will be determined by your capture solution. Unfortunately, being in a tethered situation won't work really well for me either. Too bad I can't afford a Red with their Redcode RAW and Redcine options. I love everything that the HVX offers, but for my purposes, I have a problem with the low light graininess. I think a Panasonic P2 solution will ultimately make me the happiest, maybe an HVX big brother with a full 1920x1080 chip. Is anyone expecting a new prosumer Panasonic release in the next 3-6 months?
 
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