Hello Kyle,
07 July, 2000, 18:16:06, you wrote:
KE> I have a few comments here. Though I'm not sure if the original options
KE> that Paul outlined are viable, some of what Max states here is not entirely
KE> correct. USB runs at 12 Mbs. The parallel cable runs at 2.5 Mbs.
Indeed. Here are the points I was wrong at, and stand corrected now:
[ MB is a megabyte while Mb is a megabit, 8Mb=1MB ]
I was talking that USB runs at 2.5 MB/s, but I was wrong: in fact, it
runs at 12 Mb/s, but that figures to just 1.5 MB/s. So the
uncompressed video stream is *4 times the capacity of USB*.
I was also wrong in another thing: I assumed that video cameras will
send uncompressed video to the PC. This is probably not correct, since
most digital cameras compress the video on-the-fly while recording (is
it MPEG, or something else? is there a video expert around?), so it
would be logical to assume that the stream sent to PC will be
_compressed_, and then, assuming at least 1:5 compression, USB
interface will be sufficient.
As can be seen from the following, the standard parallel is 115 KB/s
(about 1 Mb/s), but the ECP parallel (I assume this is what you've
meant) is 3 MB/s -> 24 Mb/s, and not 2.5 Mb/s.
[proof from : http://www.usb.org/faq/ans2.html#q1 ]
serial port: 115kbits/s (.115Mbits/s)
standard parallel port: 115kBYTES/s (.115MBYTES/s)
USB: 12Mbits/s (1.5MBYTES/s)
ECP/EPP parallel port: 3MBYTES/s
IEEE-1394: 100-400Mbits/s (12.5--50MBYTES/s)
[end proof]
And, to close the interfaces topic, here is another quote from
usb.org (IEEE-1394 is the FireWire interface I mentioned):
" Q8: So how does USB compare to IEEE-1394?
A8: While the two serial buses seem similar, they are intended to
fulfill different bandwidth and cost needs. 1394 can move more data in
a given amount of time, but is considerably more expensive than USB
due to its more complex protocol and signaling rate. Applications that
are best suited for 1394 are disk drives, high quality video streams
and other high bandwidth applications; all higher end consumer
devices. USB is appropriate for middle and low bandwidth applications
such as audio, scanners, printers, keyboards, and mice. USB and 1394
are complimentary technologies. 1394 is for devices where high
performance is a priority and price is not, while USB is for devices
where price is a priority and high performance is not."
KE> As far as video compression goes, I am no expert, but I do have a recent
KE> movie that runs at about the resolution you stated below. It is in a ".avs"
KE> file format and all two hours are compressed into two files of 245MB each.
KE> Both files fit on a single CD. Using Windows media player the files are
KE> nearly crystal clear in full-screen mode. So, two hours of video have been
KE> compressed into 500MB. I don't know how this was done, but I know it can be
KE> done. With the compression tools we have today I don't see why one hour of
KE> video would require 9GB of drive space.
I have one too, in .asf format : 2 hours -> 470 Mb. But the video is
far less from "crystal-clear", and any compression inevitably loses
some quality, and many cheap cards only capture uncompressed video;
even if they do, a "good" software compression can not keep pace with
the capture : good compression takes time. Hardware cards can, but
they are costly. So storing a capture in uncompressed for editing and
compressing the final version may be a good idea.
Ultimately, the finished 1-hour segment should take 200 to 250 Mb,
with current compression techniques; but it would require a lot more
space for proper editing.
Yours,
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