Sync Prop to DVD

T Chap

I am thinking about a way to have the Propeller follow along with a DVD, where perhaps a rear channel that is not to be heard gets recorded with a tone. The Prop is always looping checking for a different frequency, and if so it does something relative to that frequency. Is there a better way than using a sine wave to input some info from a DVD using an audio track?

Duffer

If you are producing/burning the DVD yourself, you might consider using something similar to "cue marks" (http://en.wikipedia.org/wiki/Cue_mark·). A small white dot overlayed·in the corner of the image could be detected by a photo-sensitive sensor placed in an inconspicuous location on the screen. You could even develop your own "code sequences" to outut simple commands.

Duffer

HollyMinkowski

I have done work with sub-audible control tones used over rf links.
I'm not sure how well the tones might work recorded along with
normal audio for a dvd...unless they were very low they could be audible
and if they are that low they might be filtered out.

I'd use one stereo channel for the tones and run it only to the prop.
You can use a tone decoder chip like the NE567 to detect the tone.
The chip would cost a few dollars but would save having to code a
tone detection routine for the prop.
Maybe there is no need for multiple tones, just record and send data
patterns using a single tone frequency?

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- Some mornings I wake up cranky.....but usually I just let him sleep -

Phil Pilgrim (PhiPi)

If you have to use an audio track and can spare a dedicated audio channel for it, I would suggest either DTMF, if you have a small set (16 max.) of distinct messages, or a modem signal, such as Bell 202.

If you want to inject the signal into the video portion, there's plenty of available bandwidth in the vertical blanking interval. This is where timecodes and closed-captioning data go.

I assume you're making the DVD yourself and have full control of the data that goes on it, right?

-Phil

T Chap

Yes I think the DTMF is the way. I am making the DVD and can drop tones on a track, run the track to a decoder. 16 is more than enough options. When a tone plays, the Prop does something. Timing accuracy is ok within a second or two. Thanks for the ideas.

HollyMinkowski

DTMF is a great way to do this.

Wonder why that didn't occur to me?

Inserting something directly into a video signal sounds really cool.
Overkill for this though...
If I record ntsc video using the video recording card in my pc there are
shifting patterns of dots on the top of the image but only on some channels.
It must be some sort of data up there, maybe to let automated equipment
know stuff like when commercials start...etc.

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- Some mornings I wake up cranky.....but usually I just let him sleep -

Toby Seckshund

The shifting dots, top of frame, are probably vertical interval time coce (VITC). Each field 25/30 Hz is numbered and the two frames that make up that field are flagged. This allows frame accurate edits. There is an audio version of this too, linear time code (LTC) and has its own track on the tape. Between the VITC (readable when the tape is still or at near non-standard speeds), LTC (readable over a wide speed range but not stationary) and a bit of interpilation from the control track pulses (when all else fails) tape editing was possible.

Overkill for this application though.

The "advert flag" TRHC of pic was a visual cue, it was a small block of free running 1MHz that came on at least 1 min before, and went off exactly 5 seconds to the break. This was ok when the domestic sets overscanned and there were "safe areas" that didn't get seen. Now there are no such luxuries. If the actions do not have to be frame acurate then an audio system will be the simplest. Sub-audible or super-audible could be used, that would only annoy people with humongous bass bins, children, bats and small dogs ( if you didn't filter it off )

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Style and grace : Nil point

RS_Jim

Yes Holly, You are seeing VITC as Toby Mentioned. If I remember the time code correctly there is even an area of User Bits that allowed the storing of data that could be used for any purpose the user designated. Some Times is was used for copy-write protection and even remote control. In digital transmission, the same Interval of time is used to sent information including the "channel" number so that people who know their TV channel by Number not by call letters would not be totally confused by the transition to digital.

rs_jim

Post Edited (Radio Shack Jim) : 9/6/2009 12:02:33 PM GMT

Toby Seckshund

There were "user bits". We, in maintenance, used to set them to the serial numbers of the machines so that we could trace faults back. Almost caused a union walkout, when the editors thought we were spying on their work rate. Hey-Ho.

I dont think it would be easy to play with the vertical interval bits, without some specalist hardware, and so the audio route will be the way to go. Any decent editor software should allow audio possibilities. BBC TX networks used phase modulated carriers to send telemetry on transmissions and did try sub-audio to keep the network on during a programme for the deaf, which had no sound. Didn't work. (Yes, it wasn't a radio programme)

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Style and grace : Nil point

Post Edited (Toby Seckshund) : 9/6/2009 12:39:03 PM GMT

T Chap

If I wanted to get really fancy I'd stripe a channel with smpte and get a cheap midi sequencer to chase it, and fire midi notes at given times. This would be pretty close to frame accurate, maybe with a slight lag and 1 or 2 frame drift due to midi latencies. Read in the midi serial info and use case statements to interpret the values, and then take the actions needed.

Post Edited (Todd Chapman) : 9/6/2009 1:54:05 PM GMT