Screencast: cast the desktop to Cast, DLNA and AirPlay receivers

An Omarchy shell plugin: a Python/asyncio daemon that discovers network
displays and serves an encoded screen capture for them to pull, plus a
Quickshell bar widget and panel to drive it.

The screen comes from the xdg-desktop-portal ScreenCast interface (asked
for every time, never remembered), goes through GStreamer, and is served
from a local HTTP port. Desktop audio is mixed in from the default
output's monitor. The container follows the receiver: WebM/VP8 for Cast,
MPEG-TS/H.264 for DLNA, HLS for AirPlay video.

The stream port has to be reachable from the LAN, and none of these
protocols can carry a credential, so the capability is the URL: a fresh
random path per session, refused to anything off the LAN, capped at four
concurrent readers.

daemon/screencast/config.py

@@ -0,0 +1,73 @@
+"""User settings, persisted to ~/.config/screencast/config.json."""
+from __future__ import annotations
+
+from .util import config_dir, read_json, write_json
+
+DEFAULTS = {
+    "fps": 30,
+    "maxHeight": 1080,          # the capture is scaled down to this before encoding
+    "bitrate": 8000,            # kbit/s
+    "encoder": "auto",          # auto | nvenc | vaapi | x264 | vp8 | vp9
+    "audio": True,              # mix desktop audio into the stream
+    "cursor": True,             # draw the pointer into the capture
+    "port": 8011,               # local HTTP server the receiver pulls the stream from
+    "lastDevice": "",           # id of the device cast to last, for the "cast again" default
+    "autoReconnect": True,      # restart the pipeline if the receiver drops the stream
+    "portVerified": False,      # set once a receiver has actually fetched the stream
+}
+
+# Settings that only take effect on the next session (changing them mid-cast
+# restarts the pipeline instead of being ignored).
+PIPELINE_KEYS = {"fps", "maxHeight", "bitrate", "encoder", "audio", "cursor"}
+
+
+class Config:
+    def __init__(self) -> None:
+        self.path = config_dir() / "config.json"
+        self.values = dict(DEFAULTS)
+        self.values.update(read_json(self.path, {}) or {})
+
+    def __getitem__(self, key):
+        return self.values.get(key, DEFAULTS.get(key))
+
+    def get(self, key, default=None):
+        return self.values.get(key, DEFAULTS.get(key, default))
+
+    def update(self, patch: dict) -> set[str]:
+        """Apply a patch, returning the keys that actually changed."""
+        changed = set()
+        for key, value in (patch or {}).items():
+            if key not in DEFAULTS:
+                continue
+            want = _coerce(key, value)
+            if want is None or self.values.get(key) == want:
+                continue
+            self.values[key] = want
+            changed.add(key)
+        if changed:
+            self.save()
+        return changed
+
+    def save(self) -> None:
+        write_json(self.path, self.values)
+
+
+def _coerce(key, value):
+    ref = DEFAULTS[key]
+    try:
+        if isinstance(ref, bool):
+            return bool(value)
+        if isinstance(ref, int):
+            v = int(value)
+            if key == "fps":
+                return max(5, min(60, v))
+            if key == "maxHeight":
+                return max(360, min(2160, v))
+            if key == "bitrate":
+                return max(500, min(50000, v))
+            if key == "port":
+                return max(1024, min(65535, v))
+            return v
+        return str(value)
+    except (TypeError, ValueError):
+        return None