Issues Using GStreamer with v4l2 Elements

Sun Aug 14 13:00:15 UTC 2022

I’m coming back to this finally. I’ve yet to find a solution to v4l2jpegdec
not working with this specific make/model camera. It works fine with
jpegdec. With v4l2jpegdec there’s no downstream data, observable using
identity element, but I do see data upstream using identity. I’m not seeing
any errors in dmesg or in the gstreamer output if I up the debug levels.
What else can be done to try and figure out why things aren’t working?

Thanks,

Josh Q

On Fri, May 13, 2022 at 4:46 PM Nicolas Dufresne <nicolas at ndufresne.ca>
wrote:

> Le vendredi 13 mai 2022 à 14:28 -0400, Joshua Quesenberry a écrit :
> > That seems very confusingly labeled, am I missing something in the below
> high-level description? From an element's perspective, I wouldn't expect to
> be outputting to my sink pad (upstream) or capturing from my src pad
> (downstream).
> >
> > Src element -> v4l2 sink using output-io-mode ... v4l2 src using
> capture-io-mode -> Sink element
> >
> > In this example, should the elements dmabuf-import be on the upstream or
> > downstream side? Likewise with the dmabuf? I'm not certain if A) the
> > downstream is creating the dmabuf and the upstream is importing it to
> dump to
> > or B) the upstream is creating the dmabuf and the downstream is
> importing it
> > for use... it seems like maybe both work when I try?
>
> I don't see a pipeline description I could comment on. By default, all v4l2
> srcpad are dmabuf exporters. But the sink pad are not automatically
> importer, as
> this code is experimental and need some polishing and testing.
>
> >
> > Thanks!
> >
> > JQ
> >
> > -----Original Message-----
> > From: Nicolas Dufresne <nicolas at ndufresne.ca>
> > Sent: Friday, May 13, 2022 8:47 AM
> > To: Joshua Quesenberry <engnfrc at gmail.com>
> > Cc: Discussion of the development of and with GStreamer <
> gstreamer-devel at lists.freedesktop.org>
> > Subject: Re: Issues Using GStreamer with v4l2 Elements
> >
> > Le vendredi 13 mai 2022 à 00:52 -0400, Joshua Quesenberry a écrit :
> > > Hi Nicolas,
> > >
> > > Sorry for the late reply, I got covered up with other stuff and am
> > > just getting a minute to come back to this.
> > >
> > > > Just read your post, looks like you are asking about at least two
> > > > distinct issue. In one case, v4l2jpegdec does not work at all for
> > > > you. There isn't much information, have you considering prepending
> > > > jpegparse in front of it ? That may help ? Jpeg V4L2 decoder is
> > > > probably one of the least tested decoder in the v4l2 lot.
> > >
> > > Correct, two separate issues I'm running into.
> > >
> > > v4l2jpegdec works fine with one camera, but not the other. I'm setting
> > > them both up very similarly, so it escapes me what could be different
> > > to cause this behavior. I just tried jpegparse in the pipeline just
> > > before v4l2jpegdec and that didn't have any effect, still the identity
> > > just after the decode is never printed. I also tried dropping down
> > > from 1280x720 at 60fps to 1024x768 at 30fps to lessen the load a bit and
> > > that had no effect either.
> > >
> > > > In the second issue, it works, but its slow. Could it be that you
> > > > are loading the CPU ? v4l2h264enc does not automatically do
> > > > zero-copy. You can experimentally enable it passing
> output-io-mode=dmabuf-import.
> > >
> > > I suppose it could be GPU load? When I've looked for ways to measure
> > > what the GPU is doing, I've unfortunately not found much of
> > > significance. The CPU load is quite low during this testing, <10% for
> > > the gstreamer pipeline according to htop. I have a pipeline already
> > > with the output-io-modes set to dmabuf-import, but before my original
> > > post I switched everything back to auto in hopes things may start
> > > working appropriately, however that was not the case. Keep in mind
> > > that I have an identity in between the source caps and the capssetter,
> > > this is where I see the average framerate drop with v4l2h264enc
> > > present.
> > >
> > > I've found that by adding more queues to the pipeline and then setting
> > > all queues to have a leaky downstream that the average rate at the
> > > source has now climbed back up to what I expected all along, so I'm
> > > assuming the issue is a clogged up downstream affecting the upstream
> > > as far as the source? After these changes input rate is ~30fps and
> > > output to file ~15fps, which is what I'm asking for, and the CPU usage
> > > is around ~30%. Playing around with the dmabuf-import option it
> > > appears I'm able to get similar rates with a drop in CPU usage to
> > > around ~10%, very exciting!
> > >
> > > How do the v4l2 elements work with queues? What do they do when stuck
> > > in between a dmabuf-import src pad and dmabuf sink pad? They don't
> > > have io-modes to be specified (at least at the user level) and I don't
> > > see a v4l2queue or something of the like. Tomorrow I'll do some more
> > > experiments to see which queues that I've added are unnecessary.
> >
> > M2M elements have two queues, so you have output-io-mode (the sink pad)
> and capture-io-mode (for the src pad).
> >
> > >
> > > So now, camera #1 not getting through v4l2jpegdec is my major
> > > roadblock. Anyone have ideas on how to debug this one or know what
> > > could cause this behavior?
> > >
> > > FYI, I did dump additional information to the RPi Forums question a
> > > few days ago, if something else is needed, just let me know.
> > >
> > > Thanks!
> > >
> > > JQ
> > >
> > > On Mon, May 9, 2022 at 4:15 PM Nicolas Dufresne <nicolas at ndufresne.ca>
> wrote:
> > > >
> > > > Le lundi 09 mai 2022 à 12:04 -0400, Joshua Quesenberry via
> > > > gstreamer-devel a écrit :
> > > > > Hey Everyone!
> > > > >
> > > > > I’m having some trouble using the v4l2 elements on an RPi. I’ve
> > > > > posted a detailed summary on the Raspberry Pi forum. Can anyone
> > > > > lend a hand? I’m not sure how many of you are frequent users of
> > > > > the RPi, so figured I’d reach out here in parallel in case the RPi
> forum isn’t the right audience.
> > > > > https://forums.raspberrypi.com/viewtopic.php?t=334215
> > > >
> > > > Just read your post, looks like you are asking about at least two
> > > > distinct issue. In one case, v4l2jpegdec does not work at all for
> > > > you. There isn't much information, have you considering prepending
> > > > jpegparse in front of it ? That may help ? Jpeg V4L2 decoder is
> > > > probably one of the least tested decoder in the v4l2 lot.
> > > >
> > > > In the second issue, it works, but its slow. Could it be that you
> > > > are loading the CPU ? v4l2h264enc does not automatically do
> > > > zero-copy. You can experimentally enable it passing
> output-io-mode=dmabuf-import.
> > > >
> > > > Nicolas
> > > >
> > > > >
> > > > > Thanks,
> > > > >
> > > > > JQ
> > > > >
> > > > >
> > > >
> >
> >
>
>
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