[PD] pix_video: composite or Firewire ?

[simon wise]

On 16 Nov 2007, at 10:47 AM, Alexandre Quessy wrote:

> I didn't like much using Firewire (ieee1394) under GNU/Linux, since
> the driver is pretty slow.

As I understand it, if you are using DV codec with firewire you are  
going to get several frames delay (on any OS) - I guess this system  
is optimised for capturing media for editing, favouring accuracy  
rather than latency, not so good for real-time use. I have tried many  
different combinations of DV camera and capture system, always there  
are several frames delay with DV. Composite capture cards can be much  
faster, and can be better resolution too - but they get very  
expensive for higher resolutions. Without locking the camera's  
framerate and the capture card together you are always going to get a  
frame or more delay. Very high end digital mixing systems have a  
exactly one frame delay, allowing for processing the signal etc and  
all the cameras are locked in sync.

I settled on a PCI framegrabber from Eurosys, not cheap but quite  
nice, and get a delay of less than 2 frames - just fast enough to get  
away with putting the image of a performer speaking up onstage  
without the sync between live voice and image being too bad.


simon