avm1: Add is_streaming flag to Sound

`Sound.loadSound` with `isStreaming` of true causes any previously
playing audio on the same object to be stopped.

core/src/avm1/globals/sound.rs

@@ -86,6 +86,7 @@ fn attach_sound<'gc>(
                 .character_by_export_name(name)
             {
                 sound_object.set_sound(activation.context.gc_context, Some(*sound));
+                sound_object.set_is_streaming(activation.context.gc_context, false);
                 sound_object.set_duration(
                     activation.context.gc_context,
                     activation
@@ -251,6 +252,14 @@ fn load_sound<'gc>(
                 .get(1)
                 .unwrap_or(&Value::Undefined)
                 .as_bool(activation.swf_version());
+            if is_streaming {
+                // Streaming MP3s can only have a single active instance.
+                // (Previous `attachSound` instances will continue to play.)
+                if let Some(sound_instance) = sound.sound_instance() {
+                    activation.context.stop_sound(sound_instance);
+                }
+            }
+            sound.set_is_streaming(activation.context.gc_context, is_streaming);
             let future = activation.context.load_manager.load_sound_avm1(
                 activation.context.player.clone(),
                 sound,
@@ -384,6 +393,12 @@ pub fn start<'gc>(
     use swf::{SoundEvent, SoundInfo};
     if let Some(sound_object) = this.as_sound_object() {
         if let Some(sound) = sound_object.sound() {
+            if sound_object.is_streaming() {
+                // Streaming MP3s can only have a single active instance.
+                if let Some(sound_instance) = sound_object.sound_instance() {
+                    activation.context.stop_sound(sound_instance);
+                }
+            }
             let sound_instance = activation.context.start_sound(
                 sound,
                 &SoundInfo {

core/src/avm1/object/sound_object.rs

@@ -37,6 +37,11 @@ pub struct SoundObjectData<'gc> {
 
     /// Duration of the currently attached sound in milliseconds.
     duration: Option<u32>,
+
+    /// Whether this sound is an external streaming MP3.
+    /// This will be true if `Sound.loadSound` was called with `isStreaming` of `true`.
+    /// A streaming sound can only have a single active instance.
+    is_streaming: bool,
 }
 
 impl fmt::Debug for SoundObject<'_> {
@@ -64,6 +69,7 @@ impl<'gc> SoundObject<'gc> {
                 owner: None,
                 position: 0,
                 duration: None,
+                is_streaming: false,
             },
         ))
     }
@@ -115,6 +121,14 @@ impl<'gc> SoundObject<'gc> {
     pub fn set_position(self, gc_context: MutationContext<'gc, '_>, position: u32) {
         self.0.write(gc_context).position = position;
     }
+
+    pub fn is_streaming(self) -> bool {
+        self.0.read().is_streaming
+    }
+
+    pub fn set_is_streaming(self, gc_context: MutationContext<'gc, '_>, is_streaming: bool) {
+        self.0.write(gc_context).is_streaming = is_streaming;
+    }
 }
 
 impl<'gc> TObject<'gc> for SoundObject<'gc> {