codec: impl AsMut for all Context wrappers

src/codec/encoder/audio.rs

@@ -137,6 +137,12 @@ impl AsRef<Context> for Audio {
 	}
 }
 
+impl AsMut<Context> for Audio {
+	fn as_mut(&mut self) -> &mut Context {
+		&mut self.0
+	}
+}
+
 pub struct Encoder(pub Audio);
 
 impl Encoder {
@@ -186,3 +192,9 @@ impl AsRef<Context> for Encoder {
 		&self
 	}
 }
+
+impl AsMut<Context> for Encoder {
+	fn as_mut(&mut self) -> &mut Context {
+		&mut self.0
+	}
+}