Electronics > Beginners
Generating Analog Video
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vk6zgo:

--- Quote from: BradC on October 19, 2018, 08:38:37 am ---
--- Quote from: bopstar on October 19, 2018, 08:23:37 am ---I have. and none of it gave me much to work with. that is why i have renamed this thread on Generating Said Video

--- End quote ---

Generating video is easy. Sycnronising it isn't.

Perhaps having a look at some of the items in the Parallax Object Library where people use the Propeller to overlay video on composite streams might be a place to start.

When I was a kid I built a genlock to lock an Apple ][ to a composite signal from the back of a tuner and put that into a basic video mixer with fade and wipe. From memory the video effects doo-dad was an old EA project. I recall buying the blank board from RCS by mail order. Anyway, by removing the colour burst oscillator on the Apple ][ it worked in a basic fashion to overlay B&W onto a composite stream, but not very well. As I grew up and met some broadcast engineers I started to understand why.

I also tried to build a Genlock for an old Philips VCR as I had the full service manual with schematics. It was then I started to understand why they used line-stores when genlocking video.

Good times.

--- End quote ---

Back in the day, before line stores were a twinkle in the eye of their ultimate developers, every source in a TV Studio was genlocked to the local SPG.
In the earliest cases, if they went to an OB, the whole Studio was genlocked to the SPG in the OB  van.
To be really "seamless", this entailed setting up the van well in advance, opening up on that source on the day of the OB, & running till close down that way.

Alternatively, they just "went to black" & switched back to the local SPG.
(A quick loss of sync wasn't as obvious when "in black".)

A similar situation occurred, if using video direct off a broadband system.

Not long after that, the link system included a "reverse link" to send Studio blanking & syncs to the OB van, which then locked its SPG to that.(The timing difference from the link distance was undetectable by the viewer.)
That sorted things for OBs, not so much for stuff off the broadband.
Taping off the broadband, for later playback was the easiest answer, in most situations.

Line, & later, frame stores made such things a lot easier.
Berni:
Here is an example of a AVR generating RGB video:
https://www.linusakesson.net/scene/craft/

Keep in mind however that to be able to do these impressive effects required a lot of cycle accurate assembler programming. You can't do this in just C code.

He also has shown generating a composite signal using an AVR, but this requires even more incredible assembler programing to get the timing of the color carrier correct enough for a TV to understand it:
https://www.linusakesson.net/scene/phasor/index.php
bopstar:
I love his videos
BradC:

--- Quote from: vk6zgo on October 19, 2018, 09:05:15 am ---Back in the day, before line stores were a twinkle in the eye of their ultimate developers, every source in a TV Studio was genlocked to the local SPG.
--- End quote ---

As they were in this studio also, but one of the signal sources was a set of VHS edit-decks, and while they were relatively easy to Vsync, the Hsync wandered all over the place (as did the chroma). The only way to sync them up was a line-store. I recall talking to the engineer about it and his comments (aside from disparaging VHS as a whole) was that in general helical scan tape was extremely difficult to sync. Heck, even the old Ampex quads had a basic line-based TBC in them. At one point we hacked the Quad TBC to work with one of the VHS decks, but it was nothing more than a friday afternoon "I wonder if we can make this work? " thing.

Broadcast was one place I wish I'd had the opportunity to spend more time. I feel lucky to have had the little exposure I did. I still recall coming in one day to find a pile of "junk" in the corner which turned out to be an ex ABC 24 channel desk (we only had 3 cameras and a couple of other video sources). Much fun was had over the next month or so shoehorning it into the studio in place of the old JVC 8 input desk it replaced. It did take an awful lot of routeint alignment to keep it running though.
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