video source dialog zbar

  • nelson

    nelson - 2012-04-15

    The first time i use zbar after turning on the computer it works perfectly but  the next time i open it I get a strange message telling me to choose video source. This does not always happen,  like 50 percent of the time. The problem with this dialogue is  when he appears zbar doesnt start and show a message with an error  "zbar_video_open" invalid request: failed to connect to camera".
    I've tested it on 3 different laptops  and had the same problems.

    appreciate your help.


    • the dan 7890

      the dan 7890 - 2013-07-27

      Try using the Zbar for windows program at
      i had this same problem. When i tried, it works. For now

  • Jarek Czekalski

    Jarek Czekalski - 2012-04-16

    There's something wrong with Windows drivers for "video for windows". I prepared code to reproduce this and posted on Toshiba forum, to no avail. There is also no possibility to report the error directly to Windows, Microsoft. So it looks like we have only a workaround: reconnect the camera physically or uninstall its driver. After uninstalling the driver, force scanning for devices. It takes about a dozen of seconds.

    "Choose source" dialog appearing by itself means that the device is inaccessible, busy, probably not freed correctly after the previous usage. That's what I blame the drivers for, because the code frees resources correctly.

  • Jarek Czekalski

    Jarek Czekalski - 2012-04-16

    This is my attempt to make Toshiba understand the problem: forum thread.

    And this is my testing app that was removed from the above mentioned forum: vfw tester 1.0.

    The application is as simple as can be. Opens capture window, starts preview. Disconnects the driver. When you try it for a second time, but several seconds pause is needed to reproduce, it doesn't work and shows choose video source dialog. If anyone is able to use this app to convince his laptop vendor, they are welcome. I can also modify the app or document it to make it even more easy to understand. Source code is included, under GNU GPL 3, so you can also adjust it yourself.

  • klaus triendl

    klaus triendl - 2012-04-19

    I can confirm the buggy behaviour of VfW. directshow on the other hand just works.

    I have written a directshow implementation for zbar, which works great! I've already contacted Jeff and Lisa (who has written the android SDK), but both of them seem to be so busy that they haven't replied to my e-mails for weeks…

  • Jarek Czekalski

    Jarek Czekalski - 2012-04-19

    Do it the official way: submit a patch to the patches tracker. Share your work. I'm looking forward to getting it! Most of my patches here were abandoned, but I did make them public.

    If maintainers are not interested and we'll be unable to work on it without a repository, we can create a clone somewhere. But I hope it will not be necessary.

    Spadix mentioned once having made some steps towards directshow implementation. But he seems to be not interested in windows platform.

    Related threads:
    forum: "vfw or direct show"
    feature request: "Support for DirectShow in Windows - ID: 3128414" (refer to this one in your patch)

    BTW: Sorry for posting broken link to Toshiba forum. This one is correct.


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