Fix playback of encrypted videos.

Encrypted videos from Element iOS were being stored with a `.Video` extension which was confusing AVFoundation.

ElementX/Sources/Services/Timeline/TimelineController/RoomTimelineController.swift

@@ -17,6 +17,7 @@
 import Combine
 import Foundation
 import UIKit
+import UniformTypeIdentifiers
 
 class RoomTimelineController: RoomTimelineControllerProtocol {
     private let userId: String
@@ -400,8 +401,7 @@ class RoomTimelineController: RoomTimelineControllerProtocol {
             return
         }
         
-        // This is not great. We could better estimate file extension from the mimetype.
+        let fileExtension = movieFileExtension(for: timelineItem.text)
-        let fileExtension = String(timelineItem.text.split(separator: ".").last ?? "mp4")
         switch await mediaProvider.loadFileFromSource(source, fileExtension: fileExtension) {
         case .success(let fileURL):
             guard let index = timelineItems.firstIndex(where: { $0.id == timelineItem.id }),
@@ -416,6 +416,26 @@ class RoomTimelineController: RoomTimelineControllerProtocol {
         }
     }
     
+    /// Temporary method that generates a file extension for a video file name
+    /// using `UTType.movie` and falls back to .mp4 if anything goes wrong.
+    ///
+    /// Ideally Rust should be able to handle this for us, otherwise we should be
+    /// attempting to detect the file type from the data itself.
+    private func movieFileExtension(for text: String) -> String {
+        let fallbackExtension = "mp4"
+        
+        // This is not great. We could better estimate file extension from the mimetype.
+        guard let fileExtensionComponent = text.split(separator: ".").last else { return fallbackExtension }
+        let fileExtension = String(fileExtensionComponent)
+        
+        // We can't trust that the extension provided is an extension that AVFoundation will accept.
+        guard let fileType = UTType(filenameExtension: fileExtension),
+              fileType.isSubtype(of: .movie)
+        else { return fallbackExtension }
+        
+        return fileExtension
+    }
+
     private func loadFileForImageTimelineItem(_ timelineItem: ImageRoomTimelineItem) async {
         if timelineItem.cachedFileURL != nil {
             // already cached

changelog.d/419.bugfix

@@ -0,0 +1 @@
+Video playback: Fix playback of encrypted video files.