Image Processing Reference
In-Depth Information
The video interface specification supports the following:
YUV422
●
Motion JPEG
●
DV
●
MPEG-1
●
MPEG-2
●
MPEG-4 (H.264) is being worked on.
●
29.18.2
USB Caveats
Don't confuse FireWire with USB. They are different, although many of their uses are similar.
Keyring USB storage devices, smart-card readers, digital cameras, and some PDA
devices use a protocol that identifies them as mass storage devices. The operating system
should recognize this and just treat them as a disk. So when you plug in a digital camera
via USB, it may look like a disk drive on the desktop.
The same eject-and-dismount caveats apply to USB mass storage devices as apply
to FireWire. Dismounting before unplugging makes sure that everything that must be
flushed to disk has been done and there are no incomplete data records.
The capacities available on keyring-mounted USB disks are reaching useful sizes.
256 MB is just about enough on which to build a bootable Linux operating system. It is not
enough capacity to be very useful for video yet, but as capacities increase, within a few
years it might be viable for transferring video from a camera to a computer in the field.
29.19
Systems Administration
In this area, you can avoid a lot of problems by anticipating what is going on and then gen-
erating some kind of warning.
Try not to read video from the same hard-disk drive that you are writing the
output to. This can cause the hard disk to thrash. This is because it is trying
to read and write to two or more different parts of the disk surface at the
same time and has to move the head a long way back and forth. Drives are
built to withstand this, but treating your system kindly gives it a longer life-
time. You can tell when a disk is thrashing because you can hear it. The noise
is alarming and you'll have no doubt that it's happening.
For example, write a script that will measure the amount of disk space that you are
using and calculate the rate at which it is being consumed. Compare this against the space
remaining and compute a simple projection of when that space will all be filled.
Run this automatically on a regular basis and set it up to warn you with an e-mail
message when you exceed a certain threshold, measured either in terms of percentage
Search WWH ::
Custom Search