linux-kernel - Re: [RFC PATCH] media: Virtual camera driver

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Message-ID: <20260203214947.GA133801@killaraus>
Date: Tue, 3 Feb 2026 23:49:47 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Oleksandr Natalenko <oleksandr@...alenko.name>
Cc: Gergo Koteles <soyer@....hu>,
	Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
	Jarkko Sakkinen <jarkko@...nel.org>, linux-media@...r.kernel.org,
	jani.nikula@...ux.intel.com, anisse@...ier.eu,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Hans Verkuil <hverkuil@...nel.org>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Jacopo Mondi <jacopo.mondi@...asonboard.com>,
	Ricardo Ribalda <ribalda@...omium.org>,
	open list <linux-kernel@...r.kernel.org>,
	Nicolas Dufresne <nicolas@...fresne.ca>
Subject: Re: [RFC PATCH] media: Virtual camera driver

On Tue, Feb 03, 2026 at 10:39:41PM +0100, Oleksandr Natalenko wrote:
> On úterý 3. února 2026 21:36:48, středoevropský standardní čas Laurent Pinchart wrote:
> > On Tue, Feb 03, 2026 at 04:53:41PM +0200, Laurent Pinchart wrote:
> > > On Tue, Feb 03, 2026 at 03:38:06PM +0100, Oleksandr Natalenko wrote:
> > > > 
> > > > Just to share my current state of affairs:
> > > > 
> > > > * sender:
> > > > 
> > > > $ gst-launch-1.0 pipewiresrc path=<webcam_id> ! video/x-h264, width=1280, height=720, framerate=24/1 ! rtph264pay ! rtpstreampay ! udpsink host=<receiver_host> port=<receiver_port>
> > > > 
> > > > * receiver:
> > > > 
> > > > $ gst-launch-1.0 udpsrc address=<receiver_host> port=<receiver_port> ! queue ! application/x-rtp-stream,encoding-name=H264 ! rtpstreamdepay ! application/x-rtp,encoding-name=H264 ! rtph264depay ! h264parse ! openh264dec ! pipewiresink mode=provide stream-properties="properties,media.class=Video/Source,media.role=Camera" client-name=VirtualCam
> > > > 
> > > > I chose H.264 because of much lower (tenfold) traffic comparing to
> > > > MJPEG, wrapped this into RTP, opted in for OpenH264 decoder because I
> > > > read it was handling low latency streams better than avdec_h264, and
> > > > tested this setup with both Firefox and Chromium, and it actually
> > > > worked pretty reliably, so I'm impressed now.
> > > 
> > > Thank you for the update. I'll give this a try.
> > 
> > I've tried those, but as soon as Firefox is connecting, I get
> > 
> > 0:00:03.569028999 131465 0x7f85cc002030 DEBUG           pipewiresink gstpipewiresink.c:692:on_state_changed:<pipewiresink0> got stream state "error" (-1)
> > 0:00:03.569060959 131465 0x7f85cc002030 DEBUG           pipewiresink gstpipewiresink.c:692:on_state_changed:<pipewiresink0> got stream state "error" (-1)
> > 0:00:03.569070767 131465 0x7f85cc002030 WARN            pipewiresink gstpipewiresink.c:710:on_state_changed:<pipewiresink0> error: stream error: no more input formats
> > ERROR: from element /GstPipeline:pipeline0/GstPipeWireSink:pipewiresink0: stream error: no more input formats
> > Additional debug info:
> > ../pipewire-1.4.9/src/gst/gstpipewiresink.c(710): on_state_changed (): /GstPipeline:pipeline0/GstPipeWireSink:pipewiresink0
> > 
> > Maybe I should try the pipewire master branch.
> 
> I'd be glad to help, but my understanding of this "stream error: no
> more input formats" boils down only to the absence of caps identifiers
> (like those "application/x-rtp-stream"blahblah), which is not the case
> here. Also, Firefox behaves differently from Chrome when using sites
> like webcamtests, and also when using google meet. I may speculate
> Firefox more eagerly closes link to a pipewire node, but I have no
> knowledge of this at all.

No worries. I'll try to find time to investigate.

> That said, "pretty reliably" doesn't mean without issues whatsoever,
> and I manage to crash both Chrome and Firefox from time to time while
> experimenting with pipelines. Probably because I occasionally
> unintentionally feed some crap into the pipewire sink.

I wouldn't dare claiming it's perfect :-) But the projects are actively
developed, so I have good hopes issues will be fixed quickly (as long as
they're reported of course).

> FWIW, I'm using 1:1.4.10-2 pipewire packages from Arch.

I'm running 1.4.9 from Gentoo, I think I should upgrade.

-- 
Regards,

Laurent Pinchart