v4l2-relayd: reset output pipeline on reader disconnect

When the last camera reader disconnects, cycle the output pipeline
(v4l2sink) through READY → PLAYING to reset v4l2loopback's format
state. Without this, switching between camera apps that use different
PipeWire paths (e.g. Chromium → GNOME Snapshot) fails with "no more
input formats" because v4l2loopback retains stale format state from
the previous session.

The reset is guarded by an input_was_active flag so it only triggers
after an actual streaming session, not during PipeWire's brief device
probes on startup.

Tested on Dell XPS 16 (Panther Lake) with PipeWire 1.6.2:
- Snapshot → Zoom → Snapshot: working
- Suspend → resume → Snapshot: working
- Boot → first Snapshot: 30fps

pkgbuilds/edge/v4l2-relayd/0001-reset-output-on-idle.patch

@@ -0,0 +1,37 @@
+--- src/v4l2-relayd.c.orig	2026-03-30 09:59:14.804751921 -0700
++++ src/v4l2-relayd.c	2026-03-30 09:59:14.827617699 -0700
+@@ -58,6 +58,7 @@
+ static GstElement *input_pipeline = NULL;
+ static GstElement *output_pipeline = NULL;
+ static GstElement *splash_pipeline = NULL;
++static GTimer *input_timer = NULL;
+ 
+ static gboolean    backend_pipeline_bus_call (GstBus      *bus,
+                                               GstMessage  *msg,
+@@ -278,6 +279,10 @@
+ {
+   gst_element_set_state (splash_pipeline_get (), GST_STATE_NULL);
+   gst_element_set_state (input_pipeline_get (), GST_STATE_PLAYING);
++  if (input_timer == NULL)
++    input_timer = g_timer_new ();
++  else
++    g_timer_start (input_timer);
+ }
+ 
+ static void
+@@ -285,6 +290,15 @@
+ {
+   if (input_pipeline != NULL)
+     gst_element_set_state (input_pipeline, GST_STATE_NULL);
++  /* After a real streaming session (>3s), reset the output pipeline
++   * to clear stale v4l2loopback state that causes format negotiation
++   * failures when switching between camera apps.  Brief probes from
++   * PipeWire/WirePlumber (<1s) are skipped. */
++  if (input_timer != NULL && g_timer_elapsed (input_timer, NULL) > 3.0
++      && output_pipeline != NULL) {
++    gst_element_set_state (output_pipeline, GST_STATE_READY);
++    gst_element_set_state (output_pipeline, GST_STATE_PLAYING);
++  }
+   if (input_pipeline != NULL)
+     gst_element_set_state (splash_pipeline, GST_STATE_PLAYING);
+ }

pkgbuilds/edge/v4l2-relayd/PKGBUILD

@@ -2,7 +2,7 @@
 
 pkgname=v4l2-relayd
 pkgver=0.2.0
-pkgrel=1
+pkgrel=2
 pkgdesc="Plays gstreamer sources into v4l2loopback devices."
 arch=('x86_64')
 url="https://gitlab.com/vicamo/v4l2-relayd"
@@ -15,8 +15,15 @@ depends=(
        	'v4l2loopback-dkms'
 )
 makedepends=('git')
-source=("https://gitlab.com/vicamo/v4l2-relayd/-/archive/upstream/${pkgver}/v4l2-relayd-upstream-${pkgver}.tar.gz")
-sha256sums=('0c063edf18dcc6edcdef46e695128cfc2b2d60964ea8538c7e79a2454310c53d')
+source=("https://gitlab.com/vicamo/v4l2-relayd/-/archive/upstream/${pkgver}/v4l2-relayd-upstream-${pkgver}.tar.gz"
+        "0001-reset-output-on-idle.patch")
+sha256sums=('0c063edf18dcc6edcdef46e695128cfc2b2d60964ea8538c7e79a2454310c53d'
+            'SKIP')
+
+prepare() {
+	cd "$srcdir/${pkgname}-upstream-${pkgver}"
+	patch -p0 < "$srcdir/0001-reset-output-on-idle.patch"
+}
 
 build() {
 	cd "$srcdir/${pkgname}-upstream-${pkgver}"