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Jason Harrison
11-09-2003, 10:40 AM
O1. In my limited experience with downloading digital video from a JVC =
> 9500 camcorder to a hard drive using firewire, the raw video files are
> =
> huge, about 4 GB per minute of video. This means that a 60 minute =
> miniDV tape can hold approximately 120 GB of raw video data.

For DV (Digital Video) you should be seeing a bandwidth of 3.6MB/sec or
220MB/minute at NTSC (30FPS) rates. I can't find any information on
the JVC-9500 but we do not see 4GB/minute of video from our Sony
VX-2000. Are you sure that you are transferring the video using DV
(eg, Firewire) and not redigitiizing the video at a higher bandwidth?
Your 4GB/minute would correspond to about 200Mbits/frame with MJPEG
compression.

A 60 minute MiniDV tape can hold about 10GB of data.

> I noticed =
> the hard drive-based Samsung camcorder mentioned in Matt's posting =
> claims to be able to store one hour of MPEG4 video on a 1.5 GB hard =
> drive (indicating an 80:1 compression ratio). From what I have read, =
> MPEG4 is not very high quality video (similar to that recorded on a =
> standard VHS tape).

MPEG4 can be high quality at low bandwidth. Check out the DIVX encoder
which is based on MPEG4:
www.divx.com
We use it to encode our HCI experiment videos before qualitative
analysis.

> We should be striving for at least the quality of =
> MPEG2 (similar to that stored on commercial DVDs using a much lower =
> compression ratio). My question is: are there solutions that provide =
> video to a hard drive or recordable DVD that is already compressed but
> =
> of at least MPEG2 quality that we can use for biomechanics (e.g., =
> without automatic shutoff, etc.)?

There are direct to hard drive recorders -- the hard drive is an add-on
that sits between the camera and the battery and records the DV signal
from the camera rather than using tapes. The hard drive is then
connected directly to the computer so no additional transfer is
necessary. The other option is use to firewire cables between the
camera and the computer and record on the computer rather than to tape.
Not all digital camcorders can output a DV signal on Firewire at
without first recording to tape.

Here is one example of the direct to hard drive method:
http://www.focusinfo.com/products/firestore/firestore.htm
This is very expensive and is designed for "out of the lab" recording.

> 2. Given that a 60 minute miniDV tape can hold 120 GB of data (if I am
> =
> correct here), does anyone know of a way to harness that capacity and =
> use it as an inexpensive backup device for our increasingly large hard
> =
> drives?

Again, 10GB/tape is what you should be getting.

One option for Macintosh is the following -- there may be Windows
options.
http://www.versiontracker.com/dyn/moreinfo/macosx/17840
I do not recommend this because the extra wear on the camcorder may
greatly shorten its life, DVD-R's are more portable (you don't need the
camera), and digital linear tape hold more data.

-Jason
------------------------------------------------------------------------
-----
Jason Harrison, PhD
Post-Doctoral Fellow and Imager Lab Manager
Imager Laboratory for Computer Graphics, Visualization and HCI
FSC3640 - 2424 Main Mall, Vancouver BC V6T 1Z4
Cell: 604 644 8611 Lab: 604 822 2218; Fax: 604 822 8989
Web: http://www.cs.ubc.ca/~harrison

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