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Video Overlay VGA/hdmi — Parallax Forums

Video Overlay VGA/hdmi

kunal_djscoekunal_djscoe Posts: 5
edited 2012-09-23 17:42 in Propeller 1
Hello,

I have read a couple of posts regarding video overlay using propeller. I was wondering can I do video overlay on a VGA or hdmi i/p signal (1920X1080). My knowledge in AV is quite limited.

Any comments/ help is greatly appreciated.

Thank you.

Comments

  • Bill HenningBill Henning Posts: 6,445
    edited 2011-04-09 15:23
    hdmi: not possible

    vga: not possible at that resolution
  • kunal_djscoekunal_djscoe Posts: 5
    edited 2011-04-09 15:26
    Thanks for quick reply Bill. Can you guide me in the right direction. What kindof microcontroller / specialised IC might help me in my quest?
    Google has not been very kind to me on this.
  • Bill HenningBill Henning Posts: 6,445
    edited 2011-04-09 15:31
    You are welcome.

    If I was going to do overlay on hdmi, I'd use an FPGA - however you also need to reseach HDCP and its licensing, as finding unencrypted HDMI signals is approximately as rare as hen's teeth.

    The nature of the information you want to overlay also matters; as you need to build a bitmap or tilemap of the information, with the appropriate number of colors, and as such, you will need at a minimum a frame buffer for your overlay data, and a way to draw into it. Then you have to decide which of the HD modes you want to support - at a minimum I'd suggest 720p and 1080i, 1080p is a mess due to the number of potential scan rates.

    FYI, I had a potential client approach me about an HDMI overlay about six to nine months ago, but he was scared off by the development costs.
    kunal_djscoe wrote: »
    Thanks for quick reply Bill. Can you guide me in the right direction. What kindof microcontroller / specialised IC might help me in my quest?
    Google has not been very kind to me on this.
  • kunal_djscoekunal_djscoe Posts: 5
    edited 2011-04-09 15:38
    Ya all my search lead to hardcore video processor chips which are used to control LCD television and for obvious reasons they dont sell a single pieces. My objective is to display time. Hence I was hoping to find a video overlay chip like the MAX7456 (this one is composite video only) which has an internal EEPROM to store characters. Do you know if there is a chip of this nature for VGA? Never felt so much clueless in my life
  • LeonLeon Posts: 7,620
    edited 2011-04-09 15:51
    Xilinx has a lot of stuff on HDMI, like this:

    http://www.xilinx.com/support/documentation/application_notes/xapp460.pdf

    Here is their latest kit using a Spartan-6:

    http://www.xilinx.com/publications/prod_mktg/CS521_CVK_SellSht.pdf

    It's rather expensive!
  • Bill HenningBill Henning Posts: 6,445
    edited 2011-04-09 16:02
    Sorry, no.

    If its a PC of some type it is far easier to write some software to overlay a time widget.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-04-09 16:59
    I don't know why the Prop couldn't do this with VGA if all you want to overlay is something small, like time. Just because the VGA resolution is 1920x1080 doesn't mean the overlay has to use the same dot clock. Basically, all you have to do is wait for VSYNC, count HSYNCs to the starting line, delay from HSYNC in each overlay line to get to the desired horizontal position, and gate the time pixels onto the RGB pins. As long as you don't tread on the syncs, the monitor won't care where the signal came from or what dot clock was used to generate it.

    -Phil
  • Bill HenningBill Henning Posts: 6,445
    edited 2011-04-09 17:16
    You are right, that should work
    Phil Pilgrim (PhiPi) wrote: »
    I don't know why the Prop couldn't do this with VGA if all you want to overlay is something small, like time. Just because the VGA resolution is 1920x1080 doesn't mean the overlay has to use the same dot clock. Basically, all you have to do is wait for VSYNC, count HSYNCs to the starting line, delay from HSYNC in each overlay line to get to the desired horizontal position, and gate the time pixels onto the RGB pins. As long as you don't tread on the syncs, the monitor won't care where the signal came from or what dot clock was used to generate it.

    -Phil
  • RaymanRayman Posts: 14,826
    edited 2011-04-10 05:07
    I'm pretty sure we could do 720p using the TI TDS410...
  • kunal_djscoekunal_djscoe Posts: 5
    edited 2011-04-10 11:31
    Thanks Phil,

    For keeping some hope alive, now I will need some high speed switching gates for it won't I ??
    Which processor would you recommend? I mean basically how do I go about doing this. If you can guide me in the right direction, this is my first project in AV industry I am more a sensor guy.

    Kunal
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-04-10 11:54
    Take a look at the documentation for the Propeller Backpack, along with the code for its overlay program. The incoming video stream is switched in and out with back-to-back MOSFETs. The overlay signal is switched off simply by tri-stating the overlay output pins.

    I think the Propeller can do what you want, so long as largish numerals are okay. You will probably need to double-scan the Prop's internal font to provide an adequate height-to-width ratio for the overlay characters. At least you're not burdened by having to do sync separation, since those signals are available separately. Still, though, this would be a very ambitious first Propeller project. Hopefully, you've got enough time to ease into it.

    -Phil
  • kunal_djscoekunal_djscoe Posts: 5
    edited 2011-04-10 12:14
    Phil,

    I went through the documentation. However, the propeller backpack talks about NTSC (composite video)
    while I am looking more for VGA signal. Do you think I can use the backpack. Did I miss something here?

    Thanks for being co-operative
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-04-10 12:46
    No, the Backpack doesn't have VGA capability. But, except for sync separation, the overlay principles are the same. The main difference is that you will be overlaying on three color channels instead of one composite signal. You will need to design custom hardware for this app, and you will need to break new ground software-wise. You will not find a drop-in solution, and it will take considerable effort on your part to make it happen. I don't mean to discourage you -- far from it -- but you are probing territory which, AFAIK, no one else has explored.

    -Phil
  • ericballericball Posts: 774
    edited 2011-04-10 14:54
    One advantage of VGA is the hsync and vsync are separate and are TTL, so will be easy (or at least easier) to sync to.
  • SeoulBigChrisSeoulBigChris Posts: 2
    edited 2012-09-21 02:08
    I have a circuit which does this, overlay text and simple icons onto HDMI video, currently in moderate volume production. The existing firmware acts as an external closed caption decoder, but I've also implemented a news crawl for another client. As mentioned by one poster above, the price of admission to make these designs is steep, because of the HDMI and HDCP membership fees. We're using the Analog Devices HDMI/OSD chip, although there are a few others apparently available. The one from ADI seems to be most easily available and most economical, but that may have changed since we started the project in 2010.
  • TonyDTonyD Posts: 210
    edited 2012-09-21 02:35
    It sounds like you have a interesting project there. Can you post a web link to it?
  • SeoulBigChrisSeoulBigChris Posts: 2
    edited 2012-09-23 17:42
    The circuit uses the Analog Devices HDMI/OSD chip, and this part is under NDA. As a result, I'm not allowed to publish details. You can see in general the capabilities of this chip on their website here.
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