The title says it all: can you sample composite video signal with the Octatrack? What about Vpp, sync dips etc. - has anyone done it?
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Composite video doesn’t carry audio?
no it doesn’t carry audio, the waveform looks like this:
http://www.labguysworld.com/VideoCookBook_005.htm
it’s called “composite” because it has a single “wire” / analogue voltage which “combines the video information required to recreate a color picture, as well as line and frame synchronization pulses”
If you have an audio signal, it can be sampled.
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no, I don’t have an audio signal, I have a video signal 
single wire with ground RCA connector with Jack adaptor
What is the frequency range of those signals? If below 20kHz then capturing and transmitting via audio lines should be possible in theory. If not, the filters in the AD converter will make sure the signal isnt captured.
Maybe test with a soundcard with 192kHz sanpling rate?
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I understand, but that video signal can be heard?
Definitely, although it’s an interesting idea. You would probably have to code something to attenuate the signal, which I have no idea how to do.
With a mixer maybe…
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if you have an audio-interface with outputs you can use touchdesigner to load a digital video and output its rgba-values over your sound card.
sounds complicated, but is actually one of the easiest tasks you can do with it.
i am working a lot with TD and must say that such a “direct” video stream sounds much like random noise though…only through heavy filtering and processing there will be some kind of harmonics, and even then it will be very close to noise-art
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i’m pretty sure you could build a circuit to do analog-digital conversion with scaling without a huge amount of reaserch/bother.
But whether the results would be worth it, I am less sure 
There was a vid somewhere using Audacity to edit/glitch a vid file, but haven’t tried it yet.
It would HAVE to be rendered 44k.
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Only somewhat related, but check out SSTV image transmission. You could sample various sources and then “build” a new image out of them.
I don’t think it is possible to sample composite video with the octatrack, it would require a much higher sample rate.
However, it is possible to encode a video signal in an audio signal. Have you heard of PixiVisor?
And check out Alexander Zolotov’s channel, the guy has lots of wonderful projects.
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Composite video is multiple, multiplexed analog signals that span from DC all the way up into the mHz range, you can’t sample it directly as digital audio.
Pixivisor is cool, I’ve had luck encoding stuff in that, sampling the audio and then playing it back on an MPC in real time. It’s VERY lo-fi but pretty interesting.
Anyway, if you want to process composite video there is a TON of 80s and 90s broadcast euipment for sale all over the internet for next to nothing, like $30-$40 for a decent switcher with effects, for example. It can take some waiting for a good price but there’s a LOT out there, you just have to do some homework to figure out what you want to do and what you need to do it.
EDIT: databending digital video in Audacity has nothing at all in common with workign with analog video signals, composite or otherwise.
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Can I ask what the intention from a sonic point of view is?
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true, it’s the old “digital vs analog” thing, but i personally try to push people towards experimenting with lower entry-level approaches instead of purchasing an LZX-industries module for half a K just to route some composite-signal to audio
but if it’s reaaallly necessary then analog video signal-chains can be fun, but also really expensive at the end of the day…
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…u can transform composite signals into audio…and whatever is audio, can be sampled…
so, why not…get urself a magnetic field detector mic from common ground/karma elektroniks and give it a try…that can “hear” every elektric driven signal of any kind…and oldschool video signal is one of the easiest to transform…