Add serde feature

Cargo.toml

@@ -16,11 +16,12 @@ edition = "2021"
 [dependencies]
 cpal = { version = "0.15.2", optional = true }
 log = "0.4.20"
+serde = { version = "1.0.193", features = ["derive"], optional = true }
 symphonia = { version = "0.5.3", features = ["all"], optional = true }
 thiserror = "1.0.50"
 
 [features]
 default = ["use-symphonia", "playback"]
 use-symphonia = ["symphonia"] # Audio decoding support with [`symphonia`].
 playback = ["cpal"]           # Audio playback support with [`cpal`].
-                              # Disable this if you want to use kittyaudio purely as an audio library.
+                              # Disable this if you want to use kittyaudio purely as an audio library.

src/command.rs

@@ -320,6 +320,7 @@ fn sine_in_out(t: f32) -> f32 {
 
 /// Specifies what easing function to use.
 #[derive(Debug, Copy, Clone, PartialEq, Default)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub enum Easing {
     /// Linear easing.
     #[default]
@@ -432,6 +433,7 @@ impl Easing {
 
 /// Specifies what change to make to a [`crate::Sound`]. Used with [`Command`].
 #[derive(Debug, Copy, Clone, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub enum Change {
     /// Change volume value.
     Volume(f32),
@@ -449,6 +451,7 @@ pub enum Change {
 /// A command that specifies an action that is applied on a [`crate::Sound`]
 /// with an optional tween.
 #[derive(Debug, Copy, Clone, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Command {
     /// What variable to change.
     pub change: Change,
@@ -516,6 +519,7 @@ impl Tweenable for usize {
 /// A parameter (used in [`crate::Sound`]) that implements tweening the
 /// underlying value.
 #[derive(Debug, Copy, Clone, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Parameter<T: Tweenable> {
     /// Last tweened value. If no commands are running, this is the same as
     /// the previous value.

src/sound.rs

@@ -30,6 +30,7 @@ use symphonia::core::{
 
 /// Represents an audio sample. Stores a left and right channel.
 #[derive(Debug, Copy, Clone, PartialEq, Default)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Frame {
     /// Left channel value. Float.
     pub left: f32,
@@ -145,6 +146,7 @@ impl Neg for Frame {
 
 /// Specifies how quickly the sound is played.
 #[derive(Debug, Copy, Clone, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub enum PlaybackRate {
     /// The sound is playing at a speed factor of the original sample rate.
     ///