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View Full Version : DV cams, switch how many at once?



joelbialek
04-10-2003, 01:57 PM
hello all,

i'm really curious about the toaster doing a live switch with DV cameras. first off, i'm assuming you would need a separate DV card for each input since only one port can be active at a time on multiport firewire cards (someone please correct me if i'm wrong)?
second, what is the latency like for DV compared to running a composite coax line from each camera location? as a follow up, how will the DV signals' sync be affected if one camera is very close to the switcher with a shorter cable, as opposed to one being a good distance away (ex: using one of the new 50m firewire cables)?

thanks for any and all input.

sincerely,
joel

Patrick Flasch
04-10-2003, 04:32 PM
Joel,

From my experience, both Mac & PC, that on a 3 port card, all ports are hot all of the time.
But, you are limited to the total bandwidth being t-fer'd to the MBO (motherboard) bus.

You will probably see a little latency, which is common! I've seen anywhere from 3 frames tp 8 frames latency.

Hope that helps...

Patrick

johnq
04-10-2003, 06:00 PM
The Windows 2000 1394 drivers only allows one "DV camera" at a time. I don't know about XP. I know you can have a DV camera/VTR on one 1394 port and capture/transfer files to a 1394 hard drive connected to another port. However, I could not connect and use two 1394 camera devices. I expect NewTek's new VT[3] 1394 device drivers solve this problem.

john

Dan Hong
04-11-2003, 11:28 AM
Hey Joel,
I just got back from Vegas. VT[3] has a new way of handling DV so you can have unlimited DV sources and switch between them. That means if you have a 3 port card or even an 8 port hub, you can have a camera on each port and the VT[3] will recognize each separately. If you're looking to use the firewire in an image magnification situation (like at church) be forewarned, the latency is there and you'd be better served coming into the VT from one of the analog inputs. DV Latency in VT[3] has been greatly reduced but it's stil quite noticable if the audience can see the live source and the video feed at the same time.

djlithium
04-13-2003, 08:24 AM
Hey Dan.

I was not able to get down to NAB so please fill me in on something.

I am looking to do some rather scary live web streaming set ups using nothing but DV sources and a single analog audio input (off my mixboard), so the latency you speak of... would that be latency between the audio of the analog source and the DV source for audio if there was one, or if switched from DV to DV or DV to Analog.

For my needs I want to run analog audio into the toaster but I would like to know if its possible to use the DV audio from a camera source and keep that source for audio live during a switch from that camera to another.

Thoughts?

Kel.

Dan Hong
04-13-2003, 02:52 PM
Hey Kel,
The audio from the DV sources should be marginally synced to the video. The analog audio in will be of by 5 frames or so. In a streaming environment, that's not so bad. In a video reinforcement situation it's pretty gnarly.

djlithium
04-13-2003, 08:53 PM
Ok cool.

I am hoping to get some tests done in the next few weeks. I will be recoding the output to ASF/WMV for review and see how things go.

The live switches to net are what I am worried about because of the CPU suckage for WME on top of the DV video decompression. I am wondering if the delay will get worse with that running at the same time.

How about audio from a DV source being used instead? Will it survive a switch and keep running? I am wondering this cause if I can run all DV video/audio all the way through... no problems.

Let me know your thoughts on that one.

Kel.

eon5
10-15-2004, 09:57 AM
Windows actually blocks you from using more than one input at a time on most Firewire I/O boards. (Kinda crazy thing to do if you ask me)

I've spoken with NewTek Development and you should be able to use multiple Firewire cards and have one camera running into each card..

That still doesn't resolve the native latency that is part of Firewire.

Good luck with the quest!

Is that possible to do a live switch with VT4 ?

I want to stay in DV, how would that possible?

thank you

pn: i find a IEEE1394 card that works with 3 Camcorders
http://eshop.macsales.com/Catalog_Item.cfm?ID=6611&Item=IOGGIC430F

Paul Lara
10-15-2004, 11:25 AM
i find a IEEE1394 card that works with 3 Camcorders
http://eshop.macsales.com/Catalog_Item.cfm?ID=6611&Item=IOGGIC430F

Well, while there are three ports on this $30 card, I suspect there's only one video decoder, meaning it could reliably bring in one DV stream to the VT switcher.

eon5
10-15-2004, 04:27 PM
Hey Joel,
VT[3] has a new way of handling DV so you can have unlimited DV sources and switch between them.

That means if you have a 3 port card or even an 8 port hub, you can have a camera on each port and the VT[3] will recognize each separately.

enlightme please ! ;)

ScorpioProd
10-15-2004, 10:25 PM
I'm not sure what Paul means about a "video decoder", there's no such thing on a firewire card, a firewire card is just a data connection, period. VT[4] handles the "video decoding" in software.

Eon5 mentions "staying DV" during this process, realize, that isn't possible. When you put ANYTHING, including firewired DV, into the switcher you are DECOMPRESSING it to uncompressed.

So, if you're thinking there would be a quality advantage to using firewire switching in a live situation, there wouldn't be.

wvp
10-15-2004, 10:49 PM
(snip) So, if you're thinking there would be a quality advantage to using firewire switching in a live situation, there wouldn't be.
There in lies the debate...
If you use camera (or tape) that sends signal as DV it starts as 5:1 compression. Uncompressed video is of course 1:1 So What is better, Keeping the DV as DV from start to finish (not possible with VT) or Taking DV and de-compressing it, then re-compressing it?
My opinion is that the difference is usually not noticeable, so I edit in DV(Firewire in) when I have long form, need the space and I use RTV(Analog in) when I have either analog video or DV footage that will use lots of layers.

bradl
10-16-2004, 12:30 AM
There in lies the debate...
If you use camera (or tape) that sends signal as DV it starts as 5:1 compression. Uncompressed video is of course 1:1 So What is better, Keeping the DV as DV from start to finish (not possible with VT) or Taking DV and de-compressing it, then re-compressing it?
Using Component in (even Composite in) does not run the video through the 5:1 DV compression so it could actually look better (uncompressed) but have some loss from the analog path, colorspace 'compression' or composite loss. Your eyes would be the final judge but the common sentiment seems to be analog input is just as good or better than DV on camera raw input.

wvp
10-16-2004, 08:03 AM
Agree. For camera input only I too would not use DV. Mostly because there is little to no difference between DV & analoge in as well as the DV puts a larger burden on the system and the cable lengths can be an issue.
Comming off tape - well, that's were my opinon on my previous post comes in to play.
Bring a DV signal in via component requires the deck (or camera) playing the DV to de-compress or convert the signal to analog. So some may say that this de-compressing & re-compressing causes a loss. But is this loss something you can see?? I don't think so.

videoconcepts
10-16-2004, 08:41 AM
One thing we might be working with here is maybe someone like me does not have an sx8 so to get multiple camera switching 1394 is the only option. Quality wise ? well it might not be good for your local TV station its most likely great for cable and dupping for customers. ( like dances and plays). Also now if you go in dv you cant go out dv. with Vt4 you can only go one way at a time. not a biggie i guess.

wvp
10-17-2004, 02:39 PM
While it is possible to use firewire for switching, it does require a pretty fast system to mak it work.
If youare doing no more than 2 camera's I would say to put the time into making it work for you. Otherwise, I would look into picking up an SX8 - imagine someone would sell one at discount.