How much data can an ordinary audio tape records

26 Jun 2005 9:02 PM

mustafaumutsarac

I am thinking to build a video camera which records to a walkman audio
tape. How much data can a ordinary audio cassette record per constant
time ?

Mustafa Umut Sarac

27 Jun 2005 12:14 AM

Cail Young

On 27/6/05 7:02 AM, in article
1119817798.669213.64***@o13g2000cwo.googlegroups.com,

"mustafaumutsa***@gmail.com" <mustafaumutsa***@gmail.com> wrote:

> I am thinking to build a video camera which records to a walkman audio
> tape. How much data can a ordinary audio cassette record per constant
> time ?
>
> Mustafa Umut Sarac
>

Compared to, say, VHS? Very, very little. If you google for 'slow scan TV'
you'll find the existing system to do this - but you can forget about using
standard audiotape for real video signals.

27 Jun 2005 12:45 PM

Laurence Payne

On 26 Jun 2005 14:02:20 -0700, mustafaumutsa***@gmail.com wrote:

>I am thinking to build a video camera which records to a walkman audio
>tape. How much data can a ordinary audio cassette record per constant
>time ?

Not enough! If you're thinking of directly recording the output of
a camera, forget it. If you are planning a slow-scan system or other
method of drastic compression, I'd be interested to hear your ideas.

28 Jun 2005 5:16 PM

JeB

On 26 Jun 2005 14:02:20 -0700, mustafaumutsa***@gmail.com wrote:

>I am thinking to build a video camera which records to a walkman audio
>tape. How much data can a ordinary audio cassette record per constant
>time ?
>

several years back there was supposed to be a Kiddi-cam coming out
for Christmas ... $99 as I recall and it recorded on to ordiary
audio cassettes. I don't know if there were technical problems or
what that it didn't make it to market.

6 Jul 2005 12:51 AM

davesvideo@aol.com

JeB said:

>>JeB Jun 28, 1:16 pm show options

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On 26 Jun 2005 14:02:20 -0700, mustafaumutsa***@gmail.com wrote:

>I am thinking to build a video camera which records to a walkman audio
>tape. How much data can a ordinary audio cassette record per constant
>time ?

several years back there was supposed to be a Kiddi-cam coming out
for Christmas ... $99 as I recall and it recorded on to ordiary
audio cassettes. I don't know if there were technical problems or
what that it didn't make it to market>>

It was on the market, but only for a year or so. Think it was
called "Pixelvision" or something like that. The technical problem was:
A small black and white subframe at low frame rate when for a little
more you could buy the kid a real camcorder.

Dave

28 Jun 2005 7:45 PM

Dave Martindale

mustafaumutsa***@gmail.com writes:

>I am thinking to build a video camera which records to a walkman audio
>tape. How much data can a ordinary audio cassette record per constant
>time ?

It depends on how you plan to do the recording, analog or digital.

A very rough analysis of analog recording: Full-quality NTSC signals
occupy about 4.5 MHz of bandwidth, PAL nearly 6 MHz. A good-quality
cassette audio tape recorder might have a useful bandwidth of 20 kHz
or so. Thus, the audio recorder can handle about 1/300 of the video
information. So you might expect to be able to transmit about one video
frame every 10 seconds (instead of 30 FPS) at full resolution, or 30 FPS
at some miniscule resolution (e.g. 32x24), or some equivalent.

In addition, that's for B&W. Colour TV encodes colour in the same space
as B&W, but it requires much better timing accuracy than a cassette
recorder has to be able to record and play back the colour information
faithfully. You're going to need a lot of additional circuitry to do
colour this way. Alternately, you can transmit reduced-resolution
colour components sequentially mixed in with the B&W data, but with a
further reduction in frame rate.

Or you can use digital recording - but you need a digital recording
method that works with an audio recorder. These tend to have even lower
effective picture rates. For example, suppose you use the equivalent of
a 56 KBPS modem to encode and decode the data. That gives you a 7
kbyte/second data rate. Raw digital video straight from a RGB camera is
about 30 megabytes/sec, so your modem-based digital recorder is a factor
of about 4000 slower than real time.

A DV camera uses moderate amounts of digital compression to reduce the
data rate to about 3 Mbytes/sec. If you managed to use a DV chipset to
do this, or built a computer system that did DV-type encoding in real time,
the recorder would only be a factor of 400 slower than real time.

Using MPEG-2 compression like DVD discs gets you down to about 750
kB/sec. You can buy standalone devices that output MPEG-2 directly over
USB. Now your audio recorder is only 100 times slower than real time,
but you're using an awful lot of sophisticated digital hardware at this
point.

Why would you want to do this, anyway?

Dave

30 Jun 2005 7:44 PM

Dimitrios Tzortzakakis

You don't mention the most important thing-that all video recorders, digital
or analog use rotating (or flying) heads to record video.This heads,
principally two, are placed on two opposite ends of a drum, that is placed
with an angle to the tape, so that each "scan" of the head leaves a "path"
on the tape, with an 30 deg.angle.This drum rotates with 3000 rpm im pal and
3600 rpm in NTSC.(VHS-making 50 fps in PAL or 60 fps in NTSC).There is also
the sync signal, or tracking, and the audio, of course-for all this you need
a 1/2 " tape, with CrO2 coating at least, and good lubricating and coating,
to not suffer damage from the rotating heads.So, audio cassetes are totally
useless.

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

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Ï "Dave Martindale" <da***@cs.ubc.ca> Ýãñáøå óôï ìÞíõìá
news:d9s9dk$6pv$1@mughi.cs.ubc.ca...
> mustafaumutsa***@gmail.com writes:
> >I am thinking to build a video camera which records to a walkman audio
> >tape. How much data can a ordinary audio cassette record per constant
> >time ?
>
> It depends on how you plan to do the recording, analog or digital.
>
> A very rough analysis of analog recording: Full-quality NTSC signals
> occupy about 4.5 MHz of bandwidth, PAL nearly 6 MHz. A good-quality
> cassette audio tape recorder might have a useful bandwidth of 20 kHz
> or so. Thus, the audio recorder can handle about 1/300 of the video
> information. So you might expect to be able to transmit about one video
> frame every 10 seconds (instead of 30 FPS) at full resolution, or 30 FPS
> at some miniscule resolution (e.g. 32x24), or some equivalent.
>
> In addition, that's for B&W. Colour TV encodes colour in the same space
> as B&W, but it requires much better timing accuracy than a cassette
> recorder has to be able to record and play back the colour information
> faithfully. You're going to need a lot of additional circuitry to do
> colour this way. Alternately, you can transmit reduced-resolution
> colour components sequentially mixed in with the B&W data, but with a
> further reduction in frame rate.
>
> Or you can use digital recording - but you need a digital recording
> method that works with an audio recorder. These tend to have even lower
> effective picture rates. For example, suppose you use the equivalent of
> a 56 KBPS modem to encode and decode the data. That gives you a 7
> kbyte/second data rate. Raw digital video straight from a RGB camera is
> about 30 megabytes/sec, so your modem-based digital recorder is a factor
> of about 4000 slower than real time.
>
> A DV camera uses moderate amounts of digital compression to reduce the
> data rate to about 3 Mbytes/sec. If you managed to use a DV chipset to
> do this, or built a computer system that did DV-type encoding in real
time,
> the recorder would only be a factor of 400 slower than real time.
>
> Using MPEG-2 compression like DVD discs gets you down to about 750
> kB/sec. You can buy standalone devices that output MPEG-2 directly over
> USB. Now your audio recorder is only 100 times slower than real time,
> but you're using an awful lot of sophisticated digital hardware at this
> point.
>
> Why would you want to do this, anyway?
>
> Dave
>