[Libav-user] list all available formats of webcam

[Hans, Sven]

Hi,

thank you for your support. Maybe you can help me a bit more:



I just tried the API, but without success.

The error is -40 (“function not implemented”) from

the function avdevice_capabilities_create. I use the libs/dlls released with ffmpeg 4.1.0 on Windows 10. My project is build with Visual Studio vc14_xp.

Maybe I did not initialize everything correctly or bad ordering of open input?

Please see my code:



const char* szUrl = "video=@device_pnp_\\?\usb#vid_046d&pid_082d&mi_00#7&1d276e35&0&0000#{65e8773d-8f56-11d0-a3b9-00a0c9223196}\global"


// register all codecs and devices

av_register_all();

avcodec_register_all();

avdevice_register_all();

av_log_set_level(AV_LOG_ERROR); //turn off info and warning; only output error

AVFormatContext* m_pFormatCtxInCam = avformat_alloc_context();

AVInputFormat* m_pInFrmt = av_find_input_format("dshow");


AVDictionary *m_pInOptions = nullptr;
av_dict_set(&m_pInOptions, "video_size", "640x480", 0);
av_dict_set(&m_pInOptions, "framerate", "30", 0);

int ret = avformat_open_input(&m_pFormatCtxInCam, szUrl, m_pInFrmt, &m_pInOptions)
if(ret >= 0)
{

  AVDeviceCapabilitiesQuery * pDevCap = nullptr;

  AVOptionRanges * pPixFmtRange;

  ret = avdevice_capabilities_create(&pDevCap, m_pFormatCtxInCam, nullptr);

  if(ret >= 0)

  {

    if(av_opt_query_ranges(&pPixFmtRange, pDevCap, "pixel_format",

       AV_OPT_MULTI_COMPONENT_RANGE) >= 0)

    {

      std::cout << "found some pixel formats" << std::endl;

    }

    av_opt_freep_ranges(&pPixFmtRange);

  }

  else

  {

    char szErrbuf[1024];

    av_strerror(ret, szErrbuf, 1024);

  }

  avdevice_capabilities_free(&pDevCap, m_pFormatCtxInCam);

}

Mit freundlichen Grüßen / Best regards

Sven Hans
DERMALOG Identification Systems GmbH
Systems Engineer

Mittelweg 120 | 20148 Hamburg
Fon +49 40 413227 0

Fax +49-40-413227-40

Mail Sven.Hans at dermalog.com<mailto:Sven.Hans at dermalog.com>

Web www.dermalog.com<https://www.dermalog.com>


This e-mail may contain information that is confidential or proprietary to DERMALOG Identification Systems GmbH. Any unauthorized disclosure, distribution or other use is prohibited.

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From: Libav-user <libav-user-bounces at ffmpeg.org> On Behalf Of Hristo Ivanov
Sent: Mittwoch, 17. April 2019 11:44
To: This list is about using libavcodec, libavformat, libavutil, libavdevice and libavfilter. <libav-user at ffmpeg.org>
Subject: Re: [Libav-user] list all available formats of webcam

Hi.

Sorry, I think I got it wrong in my previous reply:

> I think there is no way to retrieve the information using the FFMPEG API.

There is this:

https://ffmpeg.org/doxygen/trunk/structAVDeviceCapabilitiesQuery.html

Quoting the docs:

>  Following API allows user to probe device capabilities (supported codecs, pixel formats, sample formats, resolutions, channel counts, etc).

Give the above API a try.

> So the output in the console comes from the backend and not from ffmpeg?

Well, the output comes from ffmpeg, it gets printed with the av_log() function.
For the decklink '-listformats' flag, the output just gets printed and it is not stored in any structure(not even in the above API) from which it can be retrieved.
That is why I had to capture the log and then parse it.

> probably I have to implement this functionality directly with Dshow in Windows and v4l2 in Linux.

Doing this with the decklink API for my case would be a better solution than the one I currently have.

Regards.

________________________________

DERMALOG Identification Systems GmbH * Mittelweg 120, 20148 Hamburg, Germany
CEO/Managing Director: Günther Mull * Commercial Register: AG Hamburg HRB 69547
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