Issues Using GStreamer with v4l2 Elements

[Nicolas Dufresne]

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
> > > 
> > > 
> >