[Gllug] Hardware requirements for video editing?

[Rich Walker]

Chris Bell <chrisbell at overview.demon.co.uk> writes:

> On Thu 10 Apr, Rich Walker wrote:
> > 
> > Chris Bell <chrisbell at overview.demon.co.uk> writes:
> 
> > > 
> > > 
> > > Do standard camcorders aimed at the UK market run at 30 rather than 24/25
> > > frames per second?
> > 
> > I don't know; that's one of the speeds in the Firewire spec, ISTR. From
> > /usr/include/libdc1394/dc1394_control.h:
> > 
>    I was just trying to figure out the optimum screen rate. I think that
> computer screen images have shorter decay times than ordinary TV screens, so
> do not reduce flicker as much. The optimum would probably be locked to twice
> the picture rate, as long as this does not result in obvious beat patterns.
> Standard UK analogue broadcast is 50 interlaced frames per second, 25
> pictures per second, and everything used to be locked to 50Hz mains to
> reduce the effects of mains hum.

Right; so if the camera *is* producing 30fps, you'll need to filter the
output to get 25 before you start.

>    Broadcast video is compressed as near as possible to the final
> transmitter so as to avoid degradation due to multiple processing, and
> the

We did some tests a while ago with photo's and JPEG. Since Richard
Greenhill runs a photolibrary, we took a photo and JPEG'd it ~20
times. The before and after were printed, and handed around. *Everyone*
picked the original - as the one that had been repeatedly JPEG'd.

It's true that if you use a high degree of compression, the artifacts
will rapidly become intolerable. However, jpeg'ing the frames (or using
some other codec) to a high quality produces such a great reduction in
data size for little cost that it's almost always worth doing. 

> equipment is designed to cope with very high data rates. There are systems
> specifically designed as instant replay recorders using a huge box of hard
> disc drives, able to store 20 minutes of sound and video, as well as slow

Yes, I'm aware that in the past this kind of thing was necessary. Modern
hard drive thruput and sizes suggest that small RAID-0 or RAID-5 arrays
with 5400rpm drives can attain good performance, and when backed up with
motherboards with a couple of gig of ram on board, *great* performance.

> motion replay systems using modified cameras and videotape recorders running
> at 3 times the normal rate, so that the replay can be slowed without too
> much jitter, but unfortunately they are not within the available
> budget.

I can imagine!

cheers, Rich.

> 
> 
> -- 
> Chris Bell


-- 
rich walker | technical person | Shadow Robot Company | rw at shadow.org.uk
front-of-tshirt space to let     251 Liverpool Road   |
                                 London  N1 1LX       | +UK 20 7700 2487

-- 
Gllug mailing list  -  Gllug at linux.co.uk
http://list.ftech.net/mailman/listinfo/gllug