Composite Video INPUT?


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by 0808north » Tue Oct 16, 2012 11:03 am
Hello,

The RPi's Broadcast BCM2835 SoC provides hardware digital-to-analogue decoder (ie. composite video output), but I guess - like most similar SoCs - it must have a hardware analoge-to-digital encoder in the form of a composite video input. I've searched the internet for days and found no clear information. There are 2 simple answers to this post:

(1) The Broadcom SoC itself does not have a composite video input pin (hardware encoder)
(2) The Broadcom SoC does have a composite video input pin, and hardware encoder section, but it is not wired/implemented on the RPi

I'm guessing the answer is (2)... It's just not implemented on the RPi due to it not being considered an important feature. It seems the Broadcom datasheet doing the rounds does not have a schematic detailing all pin-outs. Anyone know for sure, please?

BTW, yes, I'm aware of the camera port, etc. We're talking purely CBVS 75ohm 1V p-p PAL composite video here.

Cheers,
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by LuaPie » Sun Nov 04, 2012 3:44 pm
I'm assuming they/3rd party manufacturer will eventually release a video capture add-on with composite, S-Video and SCART video inputs that plugs into the camera port. And then you will be able to encode this video with the built in h264 hardware encoder.

Or maybe it's as simple as soldering a wire from the SCART lead onto the camera port and then you will have composite video input from any device you want.
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by Burngate » Sun Nov 04, 2012 6:33 pm
Like many people on here, I have no knowledge but am willing to share ;)

Two points:
Decoding a Pal signal to digits is rather more complicated than the reverse
and
The SoC was designed (I believe) for a phone. I've not seen a phone with a Pal input
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by 0808north » Sun Nov 04, 2012 9:37 pm
The camera interface is a MIPI interface. I believe there is possibly one semi manufacturer that does (or previously did) a 'bridge' IC that would take a (PAL or NTSC) CVBS input and output the data in a MIPI compatible format.

I'm sure Ebden, if he ever saw this post, would be best placed to confirm if the Broadcom SoC has an uniplimented composite video encoder (as well as decoder), in which case, tough luck for those of us who would've wanted it implemented - the Pi is great, as it is - and already has the features required for its educational 'target market'.

He could probably confirm if the SoC was primarily intended for mobile phones, as you suggest. It would definately make sense, as it has the MIPI interface after all, which is associated with Mobile Phones.
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by KenT » Sun Nov 04, 2012 9:38 pm
search for easycap or ezcap on the forums and Google. Its a USB dongle with composite video input. Not sure how well the drivers work on the Pi though.

IIRC easycap suffered from Chinese clone problems and the Kosher product was rename ezcap
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by 0808north » Sun Nov 04, 2012 9:50 pm
Yes, thanks. Seems this is the only way, but the original post is just hoping to estabish if the SoC could perform this function itself (in theory, ie. if it was implemented on the PCB), as a lot of SoCs like the Broadcom which have a composite video (decoder) ouput often have a composite video input (encoder) too.
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by liz » Mon Nov 05, 2012 12:14 am
We're going to be releasing a camera board, which will deal with composite input. My hope is that we'll be ready to go before Christmas - but you know how these things work, so it's perfectly possible that we won't be ready before February-ish. We're doing our best, though!
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by JeremyF » Mon Nov 05, 2012 1:34 am
liz wrote:We're going to be releasing a camera board, which will deal with composite input. My hope is that we'll be ready to go before Christmas - but you know how these things work, so it's perfectly possible that we won't be ready before February-ish. We're doing our best, though!

Composite input on the camera board? First I've heard of this...

Exciting news! Now I really cant' wait :)
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by 0808north » Mon Nov 05, 2012 8:31 am
Me too. I know a lot of people will find this very exciting, educationally and commercially.
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by redhawk » Mon Nov 05, 2012 10:19 am
liz wrote:We're going to be releasing a camera board, which will deal with composite input. My hope is that we'll be ready to go before Christmas - but you know how these things work, so it's perfectly possible that we won't be ready before February-ish. We're doing our best, though!


Any chance of including y/c video capture (s-video) or is the PI limited to analogue composite signals only??

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by jamesh » Mon Nov 05, 2012 1:12 pm
0808north wrote:Yes, thanks. Seems this is the only way, but the original post is just hoping to estabish if the SoC could perform this function itself (in theory, ie. if it was implemented on the PCB), as a lot of SoCs like the Broadcom which have a composite video (decoder) ouput often have a composite video input (encoder) too.


Are you sure? I've worked on the Videocore for 4 years, first I've heard it might have a composite IN. Not saying it's not there, just I've never heard of it being used if it is.

That notwithstanding, everyone's is going HDMI nowadays anyway, and composite is a bit pants in comparison.
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by 0808north » Tue Nov 13, 2012 5:51 pm
jamesh wrote:
Are you sure? I've worked on the Videocore for 4 years, first I've heard it might have a composite IN. Not saying it's not there, just I've never heard of it being used if it is.

That notwithstanding, everyone's is going HDMI nowadays anyway, and composite is a bit pants in comparison.


The key word was 'like' the Broadcom SoC. ...Granted, I'm talking mainly DVR SoCs and CCTV SoCs (eg. Texas Instruments), but the analogue PAL or NTSC composite video signal is still very much alive and digital signals (USB, HDMI, etc) are still limited in cabling/distance, (for a lot of inductrial applications) unlike balanced analogue Composite feeds. In short, it would be a nice project to use a RPi as a DVR with both Analogue video IN to complement its Analogue video OUT and experiement with multichannel camera recording, etc.

As I said in an earlier post, I love the RPi and its an eductaional tool, but us folk can't help thinking of other uses and project! :)
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by jamesh » Tue Nov 13, 2012 7:40 pm
Sorry to be the bearer of bad tidings, but I think Liz was incorrect stating that the camera board would have composite in. Certainly in it's first incarnation. We are having to strip stuff off to get it out (not composite - I don't think that was ever there), and it looks like we won't make our self imposed Xmas deadline. Soz all, but we are working hard on it. There are some pictures on Rob Bishop's twitter feed for those interested.
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by redhawk » Tue Nov 13, 2012 7:53 pm
Just to clarify are you saying the PI hardware isn't capable of composite video input or will there be an add-on board which would be separate to the video camera??

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by jamesh » Tue Nov 13, 2012 10:19 pm
redhawk wrote:Just to clarify are you saying the PI hardware isn't capable of composite video input or will there be an add-on board which would be separate to the video camera??

Richard S.


I'm saying the default Pi isn't capable of composite input (that's always been the case), and the camera module, at least the first version, will not, as far as I know, support composite in. At the moment I know of no plans for a composite input board, BUT, I am not privy to all the Foundations plans, so I could be wrong.
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by mahjongg » Tue Nov 13, 2012 10:31 pm
but I guess - like most similar SoCs - it must have a hardware analoge-to-digital encoder in the form of a composite video input.


You guess wrong!

First most similar SoC's do not have direct video inputs, and secondly it in no way can be said that even when they would it then would be a logical conclusion to assume this SoC also must have such a feature.

The only feature remotely similar to a "video input" on this SoC is the CSI camera interface, but that interface is for an intended (CCD) camera module, and such camera's have a completely different functionality and thus interfaces than composite video video-digitizers.

Its thus far from logical to assume that the "SoC has a camera input", let alone that it must have one.

Wishful thinking strikes again! :twisted:
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by 0808north » Wed Nov 14, 2012 3:24 pm
mahjongg wrote:First most similar SoC's do not have direct video inputs, and secondly it in no way can be said that even when they would it then would be a logical conclusion to assume this SoC also must have such a feature.

The only feature remotely similar to a "video input" on this SoC is the CSI camera interface, but that interface is for an intended (CCD) camera module, and such camera's have a completely different functionality and thus interfaces than composite video video-digitizers.

Its thus far from logical to assume that the "SoC has a camera input", let alone that it must have one.

Wishful thinking strikes again! :twisted:


There were no assumptions. I think you are reading too much in to "I guess that it must..." Or perhaps it's my fault, totally, for phrasing it in a bad way - or even starting the post in the first place. There are SoCs out there that do have composite video encoders AND decoders (maybe, indeed, different devices, from different manufacturers, aimed at different markets), so the original question - just asking for some expert clarification either way - was a pretty resonable enquiry. Just a 'yes or no' was adequate. And thanks jamesh for confirming (nicely).
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by mahjongg » Fri Nov 16, 2012 11:12 pm
The RPi's Broadcast BCM2835 SoC provides hardware digital-to-analogue decoder (ie. composite video output), but I guess - like most similar SoCs - it must have a hardware analoge-to-digital encoder in the form of a composite video input.
sounds like an assumption to me, can't read it any other way.
Its a (strange) assumption, that boils down to "some devices that have video D/A converters also have video A/D converters, therefore the PI with its video D/A converter must therefore also have an A/D converter", was all that I was saying.
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by razuberii » Sun Jan 20, 2013 9:08 pm
Okay, I am very interested on this post because I would like to use Raspberry Pi to process input video. However, I am not a hardware guy so I can't build the circuitry required.

I'll contribute on the hardware front as I can. I just found these ADC (Analog to Digital Converter) addon boards for Raspberry Pi: Delta sigma 8 channel 18 bits -> http://www.abelectronics.co.uk/products ... eader-Pins

They seem to be stackable if that makes a difference. Now, I'll wait for the hardware buffs to pinch in on what is needed next.

I would hope for a DVI/HDMI or even a VGA input. :) That would make a mean Adalight in middle box for a video game.
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by mahjongg » Mon Jan 21, 2013 12:13 am
sorry to bust your bubble, but these are simple low speed A/D converters. At best you can sample audio with them, (although even that will be a bit iffy, you really need a codec to do that) you certainly cannot sample video with them. None of the GPIO's has an interface that is even remotely fast enough to sample video in real time, certainly not I2C, but even SPI is far too slow.

Having studied the chip used in the camera board, I don't see how any other video signal than the signal from the camera can be accepted, so definitely no composite (or HDMI) video in!
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by Martinezjosei » Mon Aug 19, 2013 7:13 pm
What about those AV-RGA-Composite to digital USB adapters? One side takes the AV input and the other end is an USB. Will that work on the PI? Will need to read off the USB, driver?
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by plugwash » Tue Aug 20, 2013 12:08 am
mahjongg wrote:certainly not I2C, but even SPI is far too slow.

IIRC the SoC on the Pi at least theoretically supports some crazy-high SPI clocks. So it may be theoretically possible.
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by julianfday » Thu Mar 27, 2014 11:21 am
I think a chip such as the ADV7281M might be what you need, datasheet at http://www.analog.com/static/imported-files/data_sheets/ADV7281.PDF might do it. There is also a related eval board, the EVAL-ADV7281MEBZ, which you might be able to use.

I've never tried this board, so I suspect that you would need to do some I2C configuration and modify the existing CSI driver to make it all work.

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by milos_ladni » Tue Jul 15, 2014 8:17 am
Has anyone got analog video input via adv7180 or adv7281 so far?
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by mahjongg » Tue Jul 15, 2014 11:54 am
Im guessing any Video digitizer with USB (or SPI) output must have an embedded video codec, (for example a H.264 high-profile encoder) to create a reasonably slow output data rate, unless you have a very small pixel resolution, and colour depth. Only the CSI (camera) connector offers a way around that by offering a very high speed bus directly coupled to the GPU, which can do the encoding needed, but the CSI isn't compatible with cheap video digitizers like the adv7180.
For now the only solution is a USB device with a video digitizer coupled to a video encoder. and YMMV with those, as they use up a large bandwidth of the USB channel of the PI, leaving no bandwidth to also store the video signal, or send it over to the ethernet port.
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