revid/raspivid.go: wrote Stop implementation for Raspivid AVDevice implementation

revid/raspivid.go

@@ -213,3 +213,14 @@ func (r *Raspivid) Start() error {
 func (r *Raspivid) Read(p []byte) (int, error) {
 	return r.out.Read(p)
 }
+
+func (r *Raspivid) Stop() error {
+	if r.cmd == nil || r.cmd.Process == nil {
+		return errors.New("raspivid process was never started")
+	}
+	err := r.cmd.Process.Kill()
+	if err != nil {
+		return fmt.Errorf("could not kill raspivid process: %w", err)
+	}
+	return nil
+}