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Brett Lee
09-07-1995, 11:45 AM
hello again,

with all the reading i have been doing on tethered swimming and cyclic
motion, i'd forgotten to post a summary of the replies received to my
last question a few weeks ago. please forgive me.

to compensate for this oversight, i will try to briefly summarize the
conclusions i have reached based on the replies i've received. most
importantly, i would like to sincerely thank those of you who contributed.

-------conclusions-------------

1> Linear time code - LTC, such as SMPTE, can be dubbed over a previously
recorded video tape. Vertical interval time code (VITC) cannot, as it
must be inserted between frames when the video signal is recorded.

2> Recording of either LTC or VITC onto a video tape can be
accomplished by Sony and Panasonic recorders.

3> Gen-locking (or synchronizing) of the time codes as they are inserted
on the video tape seems to be how the time domain is calibrated between
cameras, although the use of an external event (described later as a 60 hz
flash of light) can also be used.

-brett || ||
**************** ||--------------------||
Brett Lee, Ph.D. || \ -- / ||
Christopher Newport University \ -- /
O: 804/594-7617 F:804/594-7772 ||
blee@powhatan.cc.cnu.edu ||
http://www.cnu.edu/~blee/homepage/ / \
********************************** _/ \_

----------original posting-------------
:) Hello,

I have a few questions regarding "time codes" (video) that I would like
to ask to the group. I realize that two of these questions could
probably be answered by calling the sales reps, however, this approach
seemed more time effective. Sorry for any inconvenence.

As usual, I will post a summary of the replies.

Thanks,
Brett Lee
blee@powhatan.cc.cnu.edu

Question 1:

SMPTE can be "dubbed" onto the audio track of a videotape, thus
retaining first generation quality. As VITC is a vertical time code
between frames (i've been told), can this also be dubbed onto a
preexisting tape, or does the insertion of VITC require a second
generation tape to be created?

Question 2:

I've been told that there are recorders capable of recording
SMPTE time codes onto a videotape while the subject/action is being
recorded. Are there also recorders capable of doing this with VITC?

Question 3:

What is used to "sync" (for quantitative analyses) the recordings of
two or more cameras? Is it some event during the motion, time codes
read by the software, or does the video system handle this during the
recording phase by "gen-locking" the cameras?


>From WIDULE@VM.CC.PURDUE.EDU Mon Aug 14 16:32:57 1995
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Date: Mon, 14 Aug 95 14:19:21 EST
From: "carol w."
Subject: Re: SMPTE && VITC time code questions
To: Brett Lee
In-Reply-To: Your message of Mon, 14 Aug 1995 11:34:24 -0400
Status: RO
X-Status:

Brett:

When I recently talked with the folks at Lafayette Instruments, I asked
them about gen-locking two cameras (because I was thanking about adding
a second camera) and I was told they have a device for not too much
money (I think it was around $125.oo) for synchronizing the two cameras.
I have the information in a file on my computer which I can't get to
while I'm here talking with you. I'll log back later and give you the
information that I have.

carol w.


>From WIDULE@vm.cc.purdue.eduTue Aug 15 20:32:13 1995
Date: Mon, 14 Aug 95 22:13:49 EST
From: "c.w."
To: Brett Lee
Subject: Re: SMPTE && VITC time code questions

Brett:

ITEM: Camera to camera interface
MODEL: #8870 CTC
PRICE: $195.00
VENDOR: Lafayette Instruments
Lafayette, IN
317-423-1505

c.w.

>From 4SKM@QUCDN.QueensU.CATue Aug 15 20:35:46 1995
Date: Tue, 15 Aug 95 08:06:50 EDT
From: Steve
To: Brett Lee
Subject: Re: SMPTE && VITC time code questions

In response to your third question, my understanding is that the Gen-lock
system enables the video tapes to have the identical time codes generated.
This would allow for quanyitaive comparisons. It performs this by allowing the
"Gen-Lock" camera to become a "slave" to the second camera. If necessary we
have a schematic diagram of the setup for synchronized cameras.


>From dan945@ix.netcom.comFri Aug 25 13:18:33 1995
Date: Fri, 25 Aug 1995 07:01:53 -0700
From: Daniel India
To: Brett Lee
Subject: Re: SMPTE && VITC time code questions

You wrote:
>
>:) Hello,
>
>I have a few questions regarding "time codes" (video) that I would
like
>to ask to the group. I realize that two of these questions could
>probably be answered by calling the sales reps, however, this approach
>seemed more time effective. Sorry for any inconvenence.
>
>As usual, I will post a summary of the replies.
>
>Thanks,
>Brett Lee
>blee@powhatan.cc.cnu.edu
>
>Question 1:
>
> SMPTE can be "dubbed" onto the audio track of a videotape,
thus
>retaining first generation quality. As VITC is a vertical time code
>between frames (i've been told), can this also be dubbed onto a
>preexisting tape, or does the insertion of VITC require a second
>generation tape to be created?
>
>Question 2:
>
> I've been told that there are recorders capable of recording
>SMPTE time codes onto a videotape while the subject/action is being
>recorded. Are there also recorders capable of doing this with VITC?
>
>Question 3:
>
> What is used to "sync" (for quantitative analyses) the
recordings of
>two or more cameras? Is it some event during the motion, time codes
>read by the software, or does the video system handle this during the
>recording phase by "gen-locking" the cameras?
>
Question 1: Motion ANalysis uses an electronic sync pulse that
encodes the video tape with a timing mark. The signal is both
electronic and audio and can be transfered to a 2nd generation tape.

I understand that SONY and Panasonic have recorders that can dub a
signal on the original tape. $$$$.

Question 2: See question one SONY

Questions3 Motion Analysis used an electronic sync timing generator to
encode the video tape with and audio and electronic mark, the SG-20
can operate up to four video cameras to enable the researcher to
reconstruct 2D capture to 3D imaging.

For more information on Motion Analysis call 707-579-6500.

Dan India
Dan945@ix.netcom.com


>From brunel@uranus.inrets.frFri Sep 1 08:35:33 1995
Date: Fri, 1 Sep 95 11:58:47 +0200
From: Nicolas Brunel
To: blee@powhatan
Subject: Re: SMPTE && VITC time code questions

Dear Brett Lee,

I'am a PhD student working on upper limb human movement so that I have to
perform some experimental studies. I utilize two type of motion analysis
system. A totaly automatic one (Elite Motion Analyser) with synchronised
infra-red cameras wich doesn't need a video recorder and a new one which is
based on the video technologies. It's composed by four video camera
(Sony CCD-TR650E Hi-8 PAL), a videocassette recorder (Sony EVO-9650P Hi-8 PAL)
connected to a PC. The experimental recording are treated by a software
(3DVision distributed by N.T.C in France) developped by a french researcher
in the area of human sport motion. I think that my experience can be usefull
to resolve your problem.

First, the video cameras I used are not capable to record any time code (audio
time code/SMPTE or video time code/VITC) while the experimental recording.
So that I have to insert a time code to a tape on which the picture and sound
are prerecorded. This operation is very easy to do with the videocassette
recorder but it's time consuming.

The major problem with video cameras is the synchronization. There is some
manufactured cameras which can be gen-locked. These cameras are expensive
due to the semi-professional technologies used (U-Matic ...). Another cheaper
solution is to combinate a simple camera with a gen-locked recorder. In this
case, one couple camera/recorder pilot the others couples of camera/recorder
and they all got the same time code which is recorded while the
experimentation.
To my part, I have to synchronize my video camera (which can't be gen-locked)
with an event during the motion. The best solution I have found is to used a
flash. With a 50Hz frame rate, only one frame is "burned" so that there is no
doubt about the motion beginning.

I want to add this remarks : some benchmark tests, perfomed with Elite system
and the other one, one demonstrate that the video is more accurate than the
automatic system.

Hope this helps,

__________________________________________________ __________________________
BRUNEL Nicolas (Ph.D student)
INRETS / LESCO
(French National Institute of Research on Transports and safety)
109, avenue Salvador Allende *.#
Case 24 ` ! ? '
69675 BRON Cedex - ~_~. _ _____ _ O
FRANCE _ -_-~_.~ __/][ ]D\____ -_~ \()\/
tel (33+) 72.36.24.26 / 72.36.24.53 - .~ /_ _____ _\ ~ ^\/\
fax (33+) 72.36.24.58 / 72.36.24.37 (@) (@) /,
e-mail : brunel@inrets.fr __________________________________________________


no stress today :)