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rhinrichs97
11-08-2003, 02:20 AM
Thanks to Matt Walker for summarizing feedback in the limitations of most digital video cameras available for us to use for motion analysis in biomechanics.

If I may, I would like to ask a couple of related questions of the group:

1. 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. 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). 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.)?

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?

Thanks for your assistance.

--Rick

Richard N. Hinrichs, Ph.D.
Dept. of Kinesiology
Arizona State University
P.O. Box 870404
Tempe, AZ 85287-0404
(1) 480-965-1624 (phone)
(1) 480-965-8108 (fax)
hinrichs@asu.edu (email)
www.public.asu.edu/~hinrichs/ (personal web page)
www.asu.edu/clas/kines/ (Dept. web page)

-----Original Message-----
From: Biomechanics and Movement Science listserver
[mailto:BIOMCH-L@NIC.SURFNET.NL]On Behalf Of Walker, Matt
Sent: Wednesday, November 05, 2003 7:58 AM
To: BIOMCH-L@NIC.SURFNET.NL
Subject: [BIOMCH-L] Summary: digital camcorder feedback


Dear BIOMCH-L Readers,

About two weeks ago I asked for suggestions regarding digital camcorders
and/or mixers to be used for observational video. Many models were
recommended, particularly from Canon, Panasonic, and Sony. One response
forewarned that some JVC cameras have tape compatability issues. A Samsung
camcorder with a 1.5Gb hard drive was mentioned
(http://www.gizmo.com.au/public/News/news.asp?articleid=1738) and may be of
interest particularly for those who require camera mobility. A digital
mixer by Videonics was said to be costly and may adversely affect the video
quality. For those who can wait, Vicon has said that they are working on a
software solution to split 2 fire-wire inputs at the PC but I am unsure
about their progress with this.

The hibernation (auto shutoff) appears to be a problem in many camcorders.
Some only hibernate if there is a tape in the camcorder, and one response
suggested that they avoid the auto shutoff by hitting record at the end of
the tape. Also mentioned was that long (>15ft) fire-wire cables are diffult
to obtain. I found longer firewire 1394 cables on one site, but they are
costly (http://www.videonics.com/products/distancedv/). You can also use
firewire repeaters (search 'IEEE 1394 repeaters') to string together
multiple 15 foot cables.

Ideally, we would like to send fire-wire inputs straight to the PC and then
split the screen. Currently we divide two S-video inputs, record onto S-VHS
tape, and convert to digital using a Dazzle Hollywood bridge. This setup
works well, however the avi files have lost some quality and are very large.
The replies have been helpful - we are now looking at some digital still
cameras that support streaming video and are less costly, while we wait on a
good digital mixer solution.

Many thanks to all who replied - individual responses follow.

Best regards,
Matthew R. Walker, MSc
Biomechanical Engineer, Motion Analysis Laboratory
Shriners Hospital for Children, Erie, PA
mrwalker@shrinenet.org

================================================== =====================
From: "Mark Jaffrey"

The hibernation shutdown 'feature' is very anoying! However, I don't think
this occurs unless there is a tape in the cam, so you should be OK on this
front. Most of the features you want require a pretty expensive cam and
most of the feature you don't need will come with those anyway! My
Panasonic NV-MX300 has a 3CCD and claims to have 1.8 Megapixel recording.
It cost me over $3000 Australian $ last year.

================================================== =====================
From: "Dr. Jack P. Callaghan, PhD"

We use panasonic and canon cameras here for many of the reasons you listed.
I believe panasonic is one of the very few brands that still offers an
adjustable shutter speed. Canon has the progressive scan (new panasonics
might but you need to check this).

================================================== =====================
From: "Nicholas J. Gryfakis, M.S."

You aren't going to find many cameras that don't have the automatic shutoff,
but with the camera we purchased, we have been able to get around it by
hitting the record button at the end of the tape. (Panasonic AG-EZ50U) We
were also looking at the Canon GL2 and the Panasonic AG-DVX100. The GL2 and
AG-DVX100 are much higher quality cameras than the AG-EZ50U, but we are
pleased with the results so far. We are collecting all of our movie data
through Workstation presently. As far as splitters are concerned, we are
waiting for Workstation to be capable of taking two firewire inputs and
split them for us. We investigated purchasing a digital splitter (by
Videonics), but it was ridiculously expensive and Richard Baker (who has
one) has said the results have been shaky.

================================================== =====================
From: "Michael Orendurff"

One more thing you'll have to look for is a firewire longer than 15 feet. I
have bugged the Vicon guys about this, but no one has come up with one of
the length needed to get sagittal and coronal views typical of most gait
labs.

================================================== =====================
From: "Dr. Stefan Schneider"

We used the Sony VX 2000 a lot, which is a semi professional camera. But the
Sony PC120 or the newest model PC330 will do the same job - all are MINIDV
camcorder - its the best technique you can get for an affordable price. Just
be carefull with JVC cameras. I made some bad experiences with that company,
because not every tape is playable on a JVC camera. For most cameras you
must have JVC-tapes.

================================================== =====================
From: "Dr. Andrew Churchill"

You might want to make sure autofocus can be turned off, if someone walks
into a scene it will focus on them and then the
background when they are not there. An alteration of focus also alters the
zoom setting slightly so you might find if you want to collect spatial
values from the footage they would have some error in there, i'm not sure
how much.

================================================== =====================
From: "Dr. Chris Kirtley, MD PhD"

Haven't seen one myself yet, but this looks ideal for motion analysis:

http://www.gizmo.com.au/public/News/news.asp?articleid=1738

================================================== =====================

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