Cancel loading assets on switching backend

Model/Player/Backends/AVPlayerBackend.swift

@@ -62,7 +62,10 @@ final class AVPlayerBackend: PlayerBackend {
 
     var aspectRatio: Double {
         #if os(iOS)
-            videoWidth! / videoHeight!
+            guard let videoWidth, let videoHeight else {
+                return VideoPlayerView.defaultAspectRatio
+            }
+            return videoWidth / videoHeight
         #else
             VideoPlayerView.defaultAspectRatio
         #endif
@@ -170,6 +173,11 @@ final class AVPlayerBackend: PlayerBackend {
         avPlayer.replaceCurrentItem(with: nil)
     }
 
+    func cancelLoads() {
+        asset?.cancelLoading()
+        composition.cancelLoading()
+    }
+
     func seek(to time: CMTime, seekType _: SeekType, completionHandler: ((Bool) -> Void)?) {
         guard !model.live else { return }
 

Model/Player/Backends/MPVBackend.swift

@@ -353,6 +353,10 @@ final class MPVBackend: PlayerBackend {
         isPlaying ? pause() : play()
     }
 
+    func cancelLoads() {
+        stop()
+    }
+
     func stop() {
         client?.stop()
     }

Model/Player/Backends/PlayerBackend.swift

@@ -69,6 +69,8 @@ protocol PlayerBackend {
 
     func setNeedsDrawing(_ needsDrawing: Bool)
     func setSize(_ width: Double, _ height: Double)
+
+    func cancelLoads()
 }
 
 extension PlayerBackend {

Model/Player/PlayerModel.swift

@@ -498,6 +498,9 @@ final class PlayerModel: ObservableObject {
         let fromBackend: PlayerBackend = from == .appleAVPlayer ? avPlayerBackend : mpvBackend
         let toBackend: PlayerBackend = to == .appleAVPlayer ? avPlayerBackend : mpvBackend
 
+        toBackend.cancelLoads()
+        fromBackend.cancelLoads()
+
         if !self.backend.canPlayAtRate(currentRate) {
             currentRate = self.backend.suggestedPlaybackRates.last { $0 < currentRate } ?? 1.0
         }