Generating Analog Video - Page 1
Forum section: electronics / beginners

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 06:33:58 am
content: I would like to sync two analog video signals for the first part of my video mixer project. the signal will the have their sync stopped and use the video signal part for modifying and effects. then the sync will be reinserted to produce the output. would anyone know where i could get help with this.Kind regards,Justin Harris

author: Rerouter
author_rank: Super Contributor
timestamp: October 19, 2018, 06:37:36 am
content: ADC - Frame buffer - Dac,Rebroadcast the delayed signals as you need?

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 06:40:25 am
content: And how would you recommend achieving this.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 19, 2018, 06:57:17 am
content: You want to genlock the sources.

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 06:58:31 am
content: Could you be more specific on that. e.g. how would I go about Genlocking the signals

author: capt bullshot
author_rank: Super Contributor
timestamp: October 19, 2018, 07:08:34 am
content: One cannot genlock an arbitrary source. The source must have a dedicated genlock input. Then you'd connect a suitable generator to all the sources genlock inputs to synchronize them to this generator. Then all your sources should output signals suitable for analog mixing. Typical consumer equipment doesn't do so, anyway, I vastly remember consumer video mixers were available back then, but they'd require special VCRs with said genlock capabilities.If genlock isn't an option, you'd need to go digital on your mixer - say digitizing the analog signals, storing a few complete frames per input. Now you could either output them in a synchronized analog way to get into an analog mixer, or just digitally mix them and output the result.Maybe you'll be able to buy an ancient unit able to synchronize an analog video signal to a master generator. You'd need one such unit (or channel in case the unit has more than one) per input of your mixer.https://en.wikipedia.org/wiki/Genlock

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 07:11:28 am
content: Thanks for your response. Based of what you said how could i store these frames. I only want to use DIP style chips so I can build this first on a breadboard.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 19, 2018, 07:17:41 am
content: Quote from: bopstar on October 19, 2018, 07:11:28 amThat's simply not possible.Try some "using your favourite internet search engine" to search for terms like frame buffer, video synchronizer, genlock, ...That stuff is rather sophisticated and you won't be able to breadboard such things with DIP style chips - or end up with some square meters of breadboardI'd try to buy an used synchronizer or genlock-able sources or whatever is required to synchronize your video signals and then start with simple analog circuitry that might perhaps work on a breadboard. Usually higher complexity or higher frequency stuff doesn't work out well on a breadboard.

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 07:21:33 am
content: Do you know where i can get these analog schematics. because I haven't been able two. and i am not worried about breadboard space as i have hundreds. but cannot afford to buy an old mixer. the final intention is to produce a mixer and effects unit with fading and keying.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 19, 2018, 07:24:29 am
content: Quote from: bopstar on October 19, 2018, 07:21:33 amSorry, no. Video stuff isn't my primary area of knowledge nor do I have experience using such stuff on my own. Just wrote what I remembered and some general thoughts.Maybe someone else here can help you more in that direction.

author: Rerouter
author_rank: Super Contributor
timestamp: October 19, 2018, 07:40:50 am
content: Variable analog delays of video signals is very hard, So my suggestion was likely a digital approach, but the frequency for the data would likely push it into arm territory which may make it hard to find in diphttps://www.maximintegrated.com/en/products/analog/video-products/MAX9526.htmlSomething like that for your ADC, takes the video input and spits out a digital stream,https://www.analog.com/media/en/technical-documentation/data-sheets/adv7170_7171.pdfand something like this to take your digital stream and spit out the recreated signal,So that would just leave you to shuffling the samples in with the correct delay, and some kind of ring buffer of memory,

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 07:42:32 am
content: if i need to use an arm chip which would most of the time be SMD do you know a good dev platform

author: Berni
author_rank: Super Contributor
timestamp: October 19, 2018, 08:04:19 am
content: Here is the sort of technology that it takes to store video frames in RAM back in the old days of trough hole:https://www.eevblog.com/forum/vintage-computing/quantel-ramcorder-digital-video-ram-store/That is the reason all professional analog video production setups use Genlock signals. It replaces this huge expensive digital monstrosity with a simple coax cable instead.These days you can do it with a single fast MCU or a FPGA along with some ADCs and DACs, but none of this will be breadboard-able. And will need a decen't bit of software to make it run.

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 08:08:48 am
content: Could you hint me on some info on generating analog video. eather via 555 timers a 74/4000 series logic. or Atmel Micro controllers as i just bought an ATMEL ICE.555 analog video thing:

author: nali
author_rank: Frequent Contributor
timestamp: October 19, 2018, 08:17:08 am
content: Here you are, a quick and dirty mixerhttp://gieskes.nl/visual-equipment/?file=schele-mixerDon't expect quality though! You need to consider that the colour reference information is encoded into composite video (colour burst) so you'll get pretty random effects. Do you have RGB available (e.g. SCART)?

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 08:18:36 am
content: Im now more interested in generating video with chips / microcntrollers of the Atmel AVR 8bit Family

author: BradC
author_rank: Super Contributor
timestamp: October 19, 2018, 08:21:12 am
content: Quote from: bopstar on October 19, 2018, 06:33:58 amHave you re-read all the information given to you in your Genlocking, Analog Sync and Analog delay lines threads from January?

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 08:23:37 am
content: I have. and none of it gave me much to work with. that is why i have renamed this thread on Generating Said Video

author: BradC
author_rank: Super Contributor
timestamp: October 19, 2018, 08:38:37 am
content: Quote from: bopstar on October 19, 2018, 08:23:37 amGenerating 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 VCRas 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.

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 08:44:17 am
content: i have used a propeller i like them but i want to make use of my expensive ATMEL ICE with some AVR's

author: vk6zgo
author_rank: Super Contributor
timestamp: October 19, 2018, 09:05:15 am
content: Quote from: BradC on October 19, 2018, 08:38:37 amBack 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.

author: Berni
author_rank: Super Contributor
timestamp: October 19, 2018, 09:11:04 am
content: 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

author: bopstar
author_rank: Regular Contributor
timestamp: October 19, 2018, 09:12:06 am
content: I love his videos

author: BradC
author_rank: Super Contributor
timestamp: October 19, 2018, 11:42:38 am
content: Quote from: vk6zgo on October 19, 2018, 09:05:15 amAs 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.