Using _isize_ instead of _usize_ for observation as per mpv documentation

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mpvipc"
-version = "1.2.0"
+version = "1.2.1"
 authors = ["Jonas Frei <freijon@pm.me>"]
 description = "A small library which provides bindings to control existing mpv instances through sockets."
 license = "GPL-3.0"

src/ipc.rs

@@ -257,7 +257,7 @@ pub fn run_mpv_command(instance: &Mpv, command: &str, args: &[&str]) -> Result<(
     }
 }
 
-pub fn observe_mpv_property(instance: &Mpv, id: &usize, property: &str) -> Result<(), Error> {
+pub fn observe_mpv_property(instance: &Mpv, id: &isize, property: &str) -> Result<(), Error> {
     let ipc_string = format!(
         "{{ \"command\": [\"observe_property\", {}, \"{}\"] }}\n",
         id, property
@@ -278,7 +278,7 @@ pub fn observe_mpv_property(instance: &Mpv, id: &usize, property: &str) -> Resul
     }
 }
 
-pub fn unobserve_mpv_property(instance: &Mpv, id: &usize) -> Result<(), Error> {
+pub fn unobserve_mpv_property(instance: &Mpv, id: &isize) -> Result<(), Error> {
     let ipc_string = format!("{{ \"command\": [\"unobserve_property\", {}] }}\n", id);
     match serde_json::from_str::<Value>(&send_command_sync(instance, &ipc_string)) {
         Ok(feedback) => {

src/lib.rs

@@ -53,7 +53,7 @@ pub enum MpvCommand {
         to: usize,
     },
     Observe {
-        id: usize,
+        id: isize,
         property: String
     },
     PlaylistNext,
@@ -66,7 +66,7 @@ pub enum MpvCommand {
         option: SeekOptions,
     },
     Stop,
-    Unobserve(usize),
+    Unobserve(isize),
 }
 
 #[derive(Debug)]
@@ -410,14 +410,14 @@ impl Mpv {
         self.run_command(MpvCommand::PlaylistNext)
     }
 
-    pub fn observe_property(&self, id: usize, property: &str) -> Result<(), Error> {
+    pub fn observe_property(&self, id: isize, property: &str) -> Result<(), Error> {
         self.run_command(MpvCommand::Observe {
             id: id,
             property: property.to_string(),
         })
     }
 
-    pub fn unobserve_property(&self, id: usize) -> Result<(), Error> {
+    pub fn unobserve_property(&self, id: isize) -> Result<(), Error> {
         self.run_command(MpvCommand::Unobserve(id))
     }