[Libav-user] list all available formats of webcam

[salsaman]

For Linux, you can use libunicap:
https://github.com/unicap/unicap/tree/master/libunicap

Sample code here:
https://github.com/salsaman/LiVES/blob/master/src/videodev.c

Regards,
Salsaman.


http://lives-video.com
https://www.openhub.net/accounts/salsaman


On Wed, Apr 17, 2019 at 11:43 AM Philippe Gorley <
philippe.gorley at savoirfairelinux.com> wrote:

> On 2019-04-17 9:03 a.m., Hristo Ivanov wrote:
> > Hi.
> >
> > The implementation of
> > 'avdevice_capabilities_create'(
> https://ffmpeg.org/doxygen/trunk/avdevice_8c_source.html#l00143)
> > starts with the following lines:
> >
> > 1 int ret; 2 av_assert0(s && caps); 3 av_assert0(s->iformat ||
> > s->oformat); 4 if ((s->oformat &&
> > !s->oformat->create_device_capabilities) || 5 (s->iformat &&
> > !s->iformat->create_device_capabilities)) 6 return AVERROR(ENOSYS);
> >
> > My guess is the -40(ENOSYS) error is returned in line 6. Can you check
> > in your code if 'm_pFormatCtxInCam->iformat->create_device_capabilities'
> > is different from null.
> > The next step would be to understand why is
> > 'm_pFormatCtxInCam->iformat->create_device_capabilities' null. With
> > ffmpeg you just have to dive in the source code and try to understand it.
> > Compiling a debug version of the ffmpeg libs/dlls is extremely useful
> > for this purpose.
>
> It is null because, while the API exists, it is not implemented. AFAIK,
> no device implements it.
>
> Source: I grepped the latest source for avdevice_capabilities_create and
> found nothing of interest.
>
> The way to go is to either parse the logs or directly use the DShow/V4L2
> libraries.
>
> You can also implement the API yourself and send the patch to the
> ffmpeg-devel mailing list. ;)
>
> >
> >  > Maybe I did not initialize everything correctly or bad ordering of
> > open input?
> >
> >> Please see my code:
> >
> >
> > The code seems correct, my only problem with the above code is in the
> > next line:
> >
> >
> >  > int ret = avformat_open_input(&m_pFormatCtxInCam, szUrl, m_pInFrmt,
> > &m_pInOptions);
> >
> > Try using no(NULL) options:
> >
> >
> > int ret = avformat_open_input(&m_pFormatCtxInCam, szUrl, m_pInFrmt,
> NULL);
> >
> > Maybe opening an input with options shuts down the querying capabilities
> > of the input, I don't really know, it's just a guess.
> >
> >
> > Regards.
> >
> >
> > _______________________________________________
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> > Libav-user at ffmpeg.org
> > https://ffmpeg.org/mailman/listinfo/libav-user
> >
> > To unsubscribe, visit link above, or email
> > libav-user-request at ffmpeg.org with subject "unsubscribe".
> >
>
> --
> Philippe Gorley
> Free Software Consultant | Montréal, Qc
> Savoir-faire Linux
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