Re: [RFC PATCH] media: Virtual camera driver

[Oleksandr Natalenko <oleksandr@natalenko.name>]

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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.

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.

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

-- 
Oleksandr Natalenko, MSE

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