Stretch the mini player's video preview to fill its frame

Wide videos showed letterbox bars in the tiny iOS mini player preview right
after the dismiss morph, which lands the video filling the preview. The
container that takes the shared player view now sets mpv's keepaspect, so
the mini player fills its frame and every other surface keeps the aspect
ratio.

Yattee/Views/Player/MPVRenderViewRepresentable.swift

@@ -18,10 +18,16 @@ struct MPVRenderViewRepresentable: UIViewRepresentable {
     /// Optional player state to update PiP availability
     var playerState: PlayerState?
 
+    /// Stretch the video to fill the view instead of letterboxing it (the mini
+    /// player's tiny preview, where bars look like a glitch).
+    var fillsFrame = false
+
     func makeUIView(context: Context) -> UIView {
         // Create a container that will hold the actual player view
         let container = MPVContainerView()
         container.backgroundColor = .black
+        container.backend = backend
+        container.fillsFrame = fillsFrame
 
         MPVLogging.log("MPVRenderViewRepresentable.makeUIView: creating container",
             details: "hasPlayerView:\(backend.playerView != nil)")
@@ -64,6 +70,10 @@ private class MPVContainerView: UIView {
     private weak var currentPlayerView: UIView?
     private let containerID = UUID()
 
+    /// Applied to the backend whenever this container takes the player view
+    weak var backend: MPVBackend?
+    var fillsFrame = false
+
     // Track all living containers to enable view transfer on deinit
     private static var livingContainers = NSHashTable<MPVContainerView>.weakObjects()
 
@@ -159,6 +169,9 @@ private class MPVContainerView: UIView {
             playerView.trailingAnchor.constraint(equalTo: trailingAnchor)
         ])
         currentPlayerView = playerView
+        #if os(iOS)
+        backend?.setVideoFillsFrame(fillsFrame)
+        #endif
         // Size it (and re-render its framebuffer) before anyone reacts to the move
         if !bounds.isEmpty {
             layoutIfNeeded()

Yattee/Views/Player/MiniPlayerView.swift

@@ -344,8 +344,13 @@ struct MiniPlayerView: View {
             if let backend = playerService?.currentBackend as? MPVBackend,
                let playerState,
                shouldMountVideoView {
+                #if os(iOS)
+                MPVRenderViewRepresentable(backend: backend, playerState: playerState, fillsFrame: true)
+                    .allowsHitTesting(false)
+                #else
                 MPVRenderViewRepresentable(backend: backend, playerState: playerState)
                     .allowsHitTesting(false)
+                #endif
             }
 
             // Thumbnail layer - on top so it can cover the black MPV view during PiP