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emeet-pixyd

Call Detection

emeet-pixyd detects video calls by monitoring which processes hold the camera device open. This works with any application — no per-app integration needed.

Mechanism

Section titled “Mechanism”

Every EMEET_PIXYD_POLL_INTERVAL (default 2s), the daemon:

  1. Identifies the current video device path (e.g., /dev/video0)
  2. Scans /proc/*/fd/* for any file descriptor pointing to that device
  3. Filters out itself and its own descendant processes
  4. If any remaining process holds the device open, the camera is “in use”

Process Tree Exclusion

Section titled “Process Tree Exclusion”

The daemon excludes itself and its descendants to avoid false positives from its own MJPEG streaming or probing:

func isDescendantOf(pid, ancestor PID) bool
// Walks /proc/*/stat to check if pid is a descendant of ancestor

Debouncing

Section titled “Debouncing”

State changes are debounced to prevent flicker. The daemon requires EMEET_PIXYD_DEBOUNCE_COUNT (default 3) consecutive agreeing cycles before triggering a state change.

Setting Default Total delay
Poll interval 2s -
Debounce count 3 6s

This means:

  • A call start is detected within ~6 seconds
  • A call end is detected within ~6 seconds
  • Momentary camera probes (e.g., from browser permission checks) don’t trigger false positives

Debounce Counters

Section titled “Debounce Counters”

Two independent counters track consecutive “in use” and “idle” readings:

// skip-validate
debounceInUse  int  // incremented when camera is in use
debounceIdle   int  // incremented when camera is idle

Both are capped at debounceCount to prevent unbounded growth.

Call Lifecycle

Section titled “Call Lifecycle”

Call Start

Section titled “Call Start”

When the debounce threshold is crossed from idle to in-use:

  1. handleCallStart() is called
  2. Depending on auto mode:
    • full: face tracking + noise cancellation + PipeWire source switch
    • tracking-only: face tracking only
    • privacy-only: nothing
    • off: nothing
  3. Desktop notification sent

Call End

Section titled “Call End”

When the debounce threshold is crossed from in-use to idle:

  1. handleCallEnd() is called
  2. Depending on auto mode:
    • full: privacy mode + audio source restored
    • tracking-only: privacy mode
    • privacy-only: privacy mode
    • off: nothing
  3. Desktop notification sent

PipeWire Integration

Section titled “PipeWire Integration”

On call start (full mode), the daemon:

  1. Finds the PIXY audio source via wpctl status
  2. Switches the default source to PIXY via wpctl set-default
  3. On call end, restores the previous default source

The findSource and setSource functions are dependency-injected for testability.

Why /proc Instead of inotify?

Section titled “Why /proc Instead of inotify?”

/proc/*/fd scanning is chosen over alternatives because:

  • Universal: works with any app, no library integration needed
  • Reliable: the fd is held open the entire time the camera is in use
  • No permissions issues: /proc is readable by the owning user
  • No kernel modules: no custom driver or kernel patch required

The tradeoff is polling overhead, but at 2s intervals with efficient /proc traversal, the impact is negligible.

Where to go next

Section titled “Where to go next”