GPS->audio interface
I'm looking for a way to take GPS time and generate a signal that can be recorded on the audio track of a video recording to time stamp it. This is so it can be aligned with other data that's collected with GPS based time. It needs to be portable/small (i.e. Something you could attach to a small camcorder, or such).
Seems that a GPS->IRIG B interface would work, but I was wondering if someone has done this already (e.g. Someone must have made a IRIG encoder in a PIC or similar)..
Another alternate is if something like a iPhone records accurate time with the video stream. (another of the data sources is an iPhone recording something else)
I think the basic requirement is accuracy to some few milliseconds (e.g. Frame rate of the video)..
(It's for a high school science project, where they want to record various things, and line them up.. I think they could deal with looking at the timestamps over many frames to do interpolation)
Anyway, cheap and cheerful consumer gear is what is sought. (so no suggestions of synthesizing SMPTE from the output of my Z3801 and feeding it to a RED camera.. We're talking AIPtek and iPhone here..)
Jim Lux
Lux, James P skrev:
I'm looking for a way to take GPS time and generate a signal that can
be recorded on the audio track of a video recording to time stamp it.
This is so it can be aligned with other data that's collected with GPS
based time. It needs to be portable/small (i.e. Something you could
attach to a small camcorder, or such).
Traditionally SMPTE 12M LTC is being used for this purpose. For most
cases it is only known as LTC but SMPTE/EBU time code is among other
names fairly common name.
Seems that a GPS->IRIG B interface would work, but I was wondering if
someone has done this already (e.g. Someone must have made a IRIG
encoder in a PIC or similar)..
I actually have a GPS with IRIG-B output in about the same size of a
Thunderbolt. If you have your own encoder in the form of a PIC/AVR then
maybe producing SMPTE LTC should be better or at least considered as an
alternative output.
Another alternate is if something like a iPhone records accurate time
with the video stream. (another of the data sources is an iPhone
recording something else)
I think the basic requirement is accuracy to some few milliseconds
(e.g. Frame rate of the video)..
SMPTE LTC encodes the frame numbers.
(It's for a high school science project, where they want to record
various things, and line them up.. I think they could deal with
looking at the timestamps over many frames to do interpolation)
SMPTE LTC should be preferred in that case, as it is something that
editing equipment understands.
Anyway, cheap and cheerful consumer gear is what is sought. (so no
suggestions of synthesizing SMPTE from the output of my Z3801 and
feeding it to a RED camera.. We're talking AIPtek and iPhone here..)
Locking the camera with a black burst GENLOCK signal with VITC does need
to be done, but the LTC may very well be practical for the purpose.
BTW. Cameras lacking GENLOCK is highly annoying, especially when they
have el cheapo crystals... el cheapo crystals is fine, as long as they
lock up to a GENLOCK when needed.
Cheers,
Magnus
On 5/10/09 11:21 AM, "Magnus Danielson" magnus@rubidium.dyndns.org wrote:
Lux, James P skrev:
I'm looking for a way to take GPS time and generate a signal that can
be recorded on the audio track of a video recording to time stamp it.
This is so it can be aligned with other data that's collected with GPS
based time. It needs to be portable/small (i.e. Something you could
attach to a small camcorder, or such).
Traditionally SMPTE 12M LTC is being used for this purpose. For most
cases it is only known as LTC but SMPTE/EBU time code is among other
names fairly common name.
Yes.. But most consumer recorders (e.g. The cheap AIPtek) don't do timecode
(or genlock, or other useful stuff)..
So what they're really looking for is someway to time align after the fact.
I actually have a GPS with IRIG-B output in about the same size of a
Thunderbolt.
Is that an off the shelf, not hideously expensive, widget? (There are other
applications...)
Another alternate is if something like a iPhone records accurate time
with the video stream. (another of the data sources is an iPhone
recording something else)
I think the basic requirement is accuracy to some few milliseconds
(e.g. Frame rate of the video)..
SMPTE LTC encodes the frame numbers.
(It's for a high school science project, where they want to record
various things, and line them up.. I think they could deal with
looking at the timestamps over many frames to do interpolation)
SMPTE LTC should be preferred in that case, as it is something that
editing equipment understands.
I don't think "real" editing gear is in the cards. Probably more like
iMovie or something on a PC.
As a model for what they're trying to do, say you were going to measure the
acceleration due to gravity by videotaping a falling object against a scale
in the background. Except that the motion is more complex.. Maybe imagine
putting an accelerometer in the "payload" of a trebuchet... And you want to
time align the position of the trebuchet components (from the video) with
the forces on the payload. That's not what they're doing, but now that I
describe it, that WOULD be a cool science project. And get away from the
"here, I built a trebuchet and launched a projectile X meters" which is kind
of tired. (get one of those analog devices 3 axis accelerometers, hook it
to a suitable datalogger..)
Anyway, cheap and cheerful consumer gear is what is sought. (so no
suggestions of synthesizing SMPTE from the output of my Z3801 and
feeding it to a RED camera.. We're talking AIPtek and iPhone here..)
Locking the camera with a black burst GENLOCK signal with VITC does need
to be done, but the LTC may very well be practical for the purpose.
BTW. Cameras lacking GENLOCK is highly annoying, especially when they
have el cheapo crystals... el cheapo crystals is fine, as long as they
lock up to a GENLOCK when needed.
That pretty well describes just about everything they'll have available.
Cheers,
Magnus
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Hi James:
You might want to get a KIWI-OSD, Video overlay of GPS precision time
stamp. It adds HH:MM:SS EEEE OOOO FFFFFF at the bottom of the image and
so can be seen in every field. They have also developed a way to
calibrate the camera shutter in relation to the frame time by using a
number of LEDs. The main use if for star occulation timing.
http://www.geocities.com/kiwi_36_nz/kiwi_osd/kiwi_osd.htm
Have Fun,
Brooke Clarke
http://www.prc68.com
Lux, James P wrote:
I'm looking for a way to take GPS time and generate a signal that can be recorded on the audio track of a video recording to time stamp it. This is so it can be aligned with other data that's collected with GPS based time. It needs to be portable/small (i.e. Something you could attach to a small camcorder, or such).
Seems that a GPS->IRIG B interface would work, but I was wondering if someone has done this already (e.g. Someone must have made a IRIG encoder in a PIC or similar)..
Another alternate is if something like a iPhone records accurate time with the video stream. (another of the data sources is an iPhone recording something else)
I think the basic requirement is accuracy to some few milliseconds (e.g. Frame rate of the video)..
(It's for a high school science project, where they want to record various things, and line them up.. I think they could deal with looking at the timestamps over many frames to do interpolation)
Anyway, cheap and cheerful consumer gear is what is sought. (so no suggestions of synthesizing SMPTE from the output of my Z3801 and feeding it to a RED camera.. We're talking AIPtek and iPhone here..)
Jim Lux
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Lux, James P skrev:
On 5/10/09 11:21 AM, "Magnus Danielson" magnus@rubidium.dyndns.org wrote:
Lux, James P skrev:
I'm looking for a way to take GPS time and generate a signal that can
be recorded on the audio track of a video recording to time stamp it.
This is so it can be aligned with other data that's collected with GPS
based time. It needs to be portable/small (i.e. Something you could
attach to a small camcorder, or such).
Traditionally SMPTE 12M LTC is being used for this purpose. For most
cases it is only known as LTC but SMPTE/EBU time code is among other
names fairly common name.
Yes.. But most consumer recorders (e.g. The cheap AIPtek) don't do timecode
(or genlock, or other useful stuff)..
They should be hackable thought.
So what they're really looking for is someway to time align after the fact.
This does not prohibit you from just recording the LTC onto the
soundtrack anyway.
I actually have a GPS with IRIG-B output in about the same size of a
Thunderbolt.
Is that an off the shelf, not hideously expensive, widget? (There are other
applications...)
I bought one of those Brandywine GPS4 devices as announced available on
the list not too long ago. Not hideously expensive IMHO.
Another alternate is if something like a iPhone records accurate time
with the video stream. (another of the data sources is an iPhone
recording something else)
I think the basic requirement is accuracy to some few milliseconds
(e.g. Frame rate of the video)..
SMPTE LTC encodes the frame numbers.
(It's for a high school science project, where they want to record
various things, and line them up.. I think they could deal with
looking at the timestamps over many frames to do interpolation)
SMPTE LTC should be preferred in that case, as it is something that
editing equipment understands.
I don't think "real" editing gear is in the cards. Probably more like
iMovie or something on a PC.
There should be editing gear that chews LTC over audio-interface. We did
frame-grabbing tricks with a cheap video-recorder, LTC on audio track
and an SGI Indy back in the days... and a remote hacked with CMOS
switches steered by a DTMF decoder so the Indy played DTMF tone-pairs on
the port, real-time decoded LTC and frame-grabbed 10 frames at the time,
rewinded, played again etc. Some of the cheap/free programmes would be
able to decode LTC and tag the pictures accordingly.
As a model for what they're trying to do, say you were going to measure the
acceleration due to gravity by videotaping a falling object against a scale
in the background. Except that the motion is more complex.. Maybe imagine
putting an accelerometer in the "payload" of a trebuchet... And you want to
time align the position of the trebuchet components (from the video) with
the forces on the payload. That's not what they're doing, but now that I
describe it, that WOULD be a cool science project. And get away from the
"here, I built a trebuchet and launched a projectile X meters" which is kind
of tired. (get one of those analog devices 3 axis accelerometers, hook it
to a suitable datalogger..)
In that case you want the line-frequency locked or traceable by other
means. You have more use for the frequency aspect than time-notation
actually, which is more handy for a matter logging which event. Still,
LTC should be easier to get locked to the phase attached to the frames,
as the infrastructure is expected to be there for some apps, but the
IRIG-B support is not expected to be there.
If you do not hack the camera to accept a reference signal (hacking the
crystal oscillator may be all you need to do), after the fact frequency
calibration can be done with either IRIG-B, LTC or just a 1 kHz sine.
Anyway, cheap and cheerful consumer gear is what is sought. (so no
suggestions of synthesizing SMPTE from the output of my Z3801 and
feeding it to a RED camera.. We're talking AIPtek and iPhone here..)
Locking the camera with a black burst GENLOCK signal with VITC does need
to be done, but the LTC may very well be practical for the purpose.
BTW. Cameras lacking GENLOCK is highly annoying, especially when they
have el cheapo crystals... el cheapo crystals is fine, as long as they
lock up to a GENLOCK when needed.
That pretty well describes just about everything they'll have available.
Well, the two initial strategies is to either hack the cameras and
replace the XO with a VCXO which locks to a 10 Mhz. Usually it is 27 MHz
and relationship to 10 MHz is fairly trivial. After the fact
synchronisation using a 1 kHz signal (such as given by TADD-2, tvb
PIC-div or something) into the audio signal would also do, if only the
audio sample rate and the video rate is locked in the el cheapo camera,
which one can hope for at least.
Cheers,
Magnus
Brooke
The KIWI-OSD is no longer available.
However some circuit detail is available at:
http://spiff.rit.edu/richmond/ritobs/kiwi/kiwi.html
It really should be reworked to use a more reliable time source such as
a GPS timing receiver.
Bruce
Brooke Clarke wrote:
Hi James:
You might want to get a KIWI-OSD, Video overlay of GPS precision time
stamp. It adds HH:MM:SS EEEE OOOO FFFFFF at the bottom of the image
and so can be seen in every field. They have also developed a way to
calibrate the camera shutter in relation to the frame time by using a
number of LEDs. The main use if for star occulation timing.
http://www.geocities.com/kiwi_36_nz/kiwi_osd/kiwi_osd.htm
Have Fun,
Brooke Clarke
http://www.prc68.com
Lux, James P wrote:
I'm looking for a way to take GPS time and generate a signal that can
be recorded on the audio track of a video recording to time stamp it.
This is so it can be aligned with other data that's collected with
GPS based time. It needs to be portable/small (i.e. Something you
could attach to a small camcorder, or such).
Seems that a GPS->IRIG B interface would work, but I was wondering if
someone has done this already (e.g. Someone must have made a IRIG
encoder in a PIC or similar)..
Another alternate is if something like a iPhone records accurate time
with the video stream. (another of the data sources is an iPhone
recording something else)
I think the basic requirement is accuracy to some few milliseconds
(e.g. Frame rate of the video)..
(It's for a high school science project, where they want to record
various things, and line them up.. I think they could deal with
looking at the timestamps over many frames to do interpolation)
Anyway, cheap and cheerful consumer gear is what is sought. (so no
suggestions of synthesizing SMPTE from the output of my Z3801 and
feeding it to a RED camera.. We're talking AIPtek and iPhone here..)
Jim Lux
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On 5/10/09 12:15 PM, "Brooke Clarke" brooke@pacific.net wrote:
Hi James:
You might want to get a KIWI-OSD, Video overlay of GPS precision time
stamp. It adds HH:MM:SS EEEE OOOO FFFFFF at the bottom of the image and
so can be seen in every field. They have also developed a way to
calibrate the camera shutter in relation to the frame time by using a
number of LEDs. The main use if for star occulation timing.
http://www.geocities.com/kiwi_36_nz/kiwi_osd/kiwi_osd.htm
Have Fun,
Brooke Clarke
Yes, but that requires getting access to the video stream, which isn't easy
in a "camcorder" environment. Separate video recorders actually cost more
than camcorders.
Lux, James P skrev:
On 5/10/09 12:15 PM, "Brooke Clarke" brooke@pacific.net wrote:
Hi James:
You might want to get a KIWI-OSD, Video overlay of GPS precision time
stamp. It adds HH:MM:SS EEEE OOOO FFFFFF at the bottom of the image and
so can be seen in every field. They have also developed a way to
calibrate the camera shutter in relation to the frame time by using a
number of LEDs. The main use if for star occulation timing.
http://www.geocities.com/kiwi_36_nz/kiwi_osd/kiwi_osd.htm
Have Fun,
Brooke Clarke
Yes, but that requires getting access to the video stream, which isn't easy
in a "camcorder" environment. Separate video recorders actually cost more
than camcorders.
What precision of anything do you need?
Expect 50-100 ppm oscillators in there.
Recorded material is compressed. Consider how that affects your readout.
Recorded material is said progressive/interlaced. This may not reflect
how the CCD is snapshot and readout. You may not have the expected 1125
or 750 lines per frame, and exactly what frame rate do you have?
Cheers,
Magnus
Hi,
low tech solution may be to produce second pips of audio with long
one minute pips,
a bit like WWV, and inject them into the mic plug (in parallel to the
mic) or use a small speaker.
That together with a clap-board start should enable any frame to be
timed.
cheers, Neville Michie
On 11/05/2009, at 3:48 AM, Lux, James P wrote:
I'm looking for a way to take GPS time and generate a signal that
can be recorded on the audio track of a video recording to time
stamp it. This is so it can be aligned with other data that's
collected with GPS based time. It needs to be portable/small (i.e.
Something you could attach to a small camcorder, or such).
Seems that a GPS->IRIG B interface would work, but I was wondering
if someone has done this already (e.g. Someone must have made a
IRIG encoder in a PIC or similar)..
Another alternate is if something like a iPhone records accurate
time with the video stream. (another of the data sources is an
iPhone recording something else)
I think the basic requirement is accuracy to some few milliseconds
(e.g. Frame rate of the video)..
(It's for a high school science project, where they want to record
various things, and line them up.. I think they could deal with
looking at the timestamps over many frames to do interpolation)
Anyway, cheap and cheerful consumer gear is what is sought. (so no
suggestions of synthesizing SMPTE from the output of my Z3801 and
feeding it to a RED camera.. We're talking AIPtek and iPhone here..)
Jim Lux
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/
time-nuts
and follow the instructions there.
On 5/10/09 4:26 PM, "Magnus Danielson" magnus@rubidium.dyndns.org wrote:
Lux, James P skrev:
On 5/10/09 12:15 PM, "Brooke Clarke" brooke@pacific.net wrote:
Hi James:
You might want to get a KIWI-OSD, Video overlay of GPS precision time
stamp. It adds HH:MM:SS EEEE OOOO FFFFFF at the bottom of the image and
so can be seen in every field. They have also developed a way to
calibrate the camera shutter in relation to the frame time by using a
number of LEDs. The main use if for star occulation timing.
http://www.geocities.com/kiwi_36_nz/kiwi_osd/kiwi_osd.htm
Have Fun,
Brooke Clarke
Yes, but that requires getting access to the video stream, which isn't easy
in a "camcorder" environment. Separate video recorders actually cost more
than camcorders.
What precision of anything do you need?
Expect 50-100 ppm oscillators in there.
Yes, but probably fairly good in the short run, and if you were recording
almost any sync signal (e.g. The 1kHz sine) you could calibrate that out.
Recorded material is compressed. Consider how that affects your readout.
Recorded material is said progressive/interlaced. This may not reflect
how the CCD is snapshot and readout. You may not have the expected 1125
or 750 lines per frame, and exactly what frame rate do you have?
I think that's something they'll need to experiment with...
Jim