Connecting Multiple Cameras to Computer for Webcasting
Dan Asks: I want to connect up to 4 Cameras to my Mac to stream and switch a multicamera production using Livestream. They can accept multiple, live cameras, but then only talk about a Firewire Camera and a USB camera at the same time which is not what I have in mind. Can I connect multiple firewire cameras into a single firewire port? How about a Firewire hub? Or what can I use to connect multiple cameras, and how would it affect the quality of picture from the cameras?
Answer: The rule of thumb for connecting multiple cameras to your computer for webcasting is this: each camera must be connected to its own separate firewire card and not daisy chained together. Your computer needs to see each camera separately.
Just because you might see multiple ports on a firewire card- this does NOT mean it’s ok to connect multiple cameras to it. Each firewire card represents a “firewire channel” to your computer. To avoid stuttering video, avoid plugging in multiple cams into one firewire card.
Most FireWire 800 controllers have a very limited number of connectors; between 2 and 3 (most laptops have just one). To connect to (for example) 4 cameras, you need to use a hub between the computer and the cameras. Many hubs tend to be rather lame, having only 3 ports, for example the hubs from Unibrain fall into this category.
A firewire hub would work as long as you don’t exceed the bandwidth of the hub or the interface. The original firewire bandwidth is 400 Mbps, and a standard DV stream is 25, so you could put 16 DV cameras on one bus. Now there’s “Firewire 800″ which could handle 32 DV cameras. Provided the computer behind it is up to the task, of course.
You also need to satisfy the power needs of the cameras. There are situations where a Macintosh laptop sees 3 cameras without issue, but cannot actually run them at the same time, because the FireWire port cannot put out enough power. This applies sometimes with plain PCI cards as well. This can be remedied by having power supplies in the hubs. Be warned that some (ancient, FW400) hubs use the power only for their own electronics, and do not deliver any power to the bus. All recent models seem to deliver power to the bus as well, powering the cameras as needed.
When using PCI cards, make sure that if there is an extra power connector on the card, it is connected. This gives the card more electricity than it could get from the PCI bus.
Unfortunately not all hubs work well on all platforms.
A few additional notes to be aware of:
1) Apple only supports one (1) DV Cameras/DV Devices, regardless of how many FW Controllers you have. DV devices normally listen and broadcast on ISOCH Channel 63. Windows supports up to two DV cameras – but how reliable that is I’m not sure due to the design of the firewire protocol used to control DV devices.
2) The number of Firewire ports on a Mac or FireWire card or FireWire Hub has nothing to do with usable bandwidth. It’s the number of FireWire OHCI Controllers that control how much bandwidth is available.
Except for some models which had two separate Firewire OHCI controllers, one at 400 and one at 800, some Macs ship with one Firewire OHCI controllers. The Apple Technical Specs for each computer indicate how many FW Controllers they have.
The only real, stable solution is to connect multiple cameras to a video mixer and connect the output of the mixer to your computer – cutting out the use of a software based video switched entirely.