need help to understand the pipeline

[Peter Maersk-Moller]

There is a negotiation between every output pad and every input in your
pipeline for every stage in the pipeline. The modules will try to find a
common format (for the part of a complete format) that has not been
specified. You specify "video/x-raw,width=1280,height=800,framerate=10/" as
a partial format specs between output pad of v4l2src (aka src) and input
pad for videoconvert (aka sink). If they both support these specs and if
they can negotiate the rest and agree (video/x-raw is a family of formats,
not a complete full spec - they need to agree on a specific format within
the family), then one of the requirements for data to flow in the pipeline
has been met. Now depending on your hardware (the camera device and how it
is connected), v4l2src can provide a range of encodings, formats,
geometries and framerates although typical only a subset of the full set of
combinations will be available..

On Fri, Jul 16, 2021 at 2:15 PM niXman via gstreamer-devel <
gstreamer-devel at lists.freedesktop.org> wrote:

>
>
> hello Maersk-Moller,
>
> thank you very much for your answer!
> but I have a few questions because something is not clear to me...
>
> On 2021-07-16 10:52, Peter Maersk-Moller via gstreamer-devel wrote:
> > Hi niXman
> >
> > You are in fact not retrieving JPEG encoded frames from your camera.
> > Apparently your camera also supports a raw video format.
>
> according to the documentation, the Omnivision OV5640 chip gives frames
> in JPEG.
> please explain why you think it is not so? how can i check in what
> format i am receiving frames actually?
>
> > Most likely this raw format is some sort of YUV format. You can find
> > out by
> > adding '-v' to gst-launch-1.0 and look for the format accepted by the
> > videoconvert sink pad.
>
> I tried, but I don't understand what I see...
> when I specify "video/x-raw" in the output it is also "video/x-raw", and
> when I specify "image/jpeg" in the output it is also "image/jpeg".
> how can this be? the camera sends frames in both formats and gstreamer
> just chooses which format to use? or how?
>
>
>
> best!
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