Fix MP4 video playback in Peek when only audio is displayed

src/modules/peek/Peek.FilePreviewer/FilePreview.xaml

@@ -60,6 +60,15 @@
             </MediaPlayerElement.TransportControls>
         </MediaPlayerElement>
 
+        <TextBlock 
+            x:Name="VideoErrorMessage" 
+            HorizontalAlignment="Center" 
+            VerticalAlignment="Center" 
+            Foreground="{StaticResource TextFillColorSecondaryBrush}" 
+            Text="{x:Bind VideoPreviewer.ErrorMessage, Mode=OneWay}" 
+            TextWrapping="Wrap" 
+            Visibility="{x:Bind IsErrorMessageVisible(VideoPreviewer), Mode=OneWay}" />
+
         <controls:AudioControl
             x:Name="AudioPreview"
             Source="{x:Bind AudioPreviewer.Preview, Mode=OneWay}"

src/modules/peek/Peek.FilePreviewer/FilePreview.xaml.cs

@@ -155,6 +155,15 @@ public Visibility IsUnsupportedPreviewVisible(IUnsupportedFilePreviewer? preview
             return isValidPreview ? Visibility.Visible : Visibility.Collapsed;
         }
 
+        public Visibility IsErrorMessageVisible(IVideoPreviewer? previewer)
+        {
+            var shouldShow = previewer != null && 
+                             MatchPreviewState(previewer.State, PreviewState.Error) && 
+                             !string.IsNullOrEmpty(previewer.ErrorMessage);
+
+            return shouldShow ? Visibility.Visible : Visibility.Collapsed;
+        }
+
         private async Task OnItemPropertyChanged()
         {
             // Cancel previous loading task

src/modules/peek/Peek.FilePreviewer/Previewers/Interfaces/IVideoPreviewer.cs

@@ -9,5 +9,7 @@ namespace Peek.FilePreviewer.Previewers.Interfaces
     public interface IVideoPreviewer : IPreviewer, IPreviewTarget
     {
         public MediaSource? Preview { get; }
+
+        public string? ErrorMessage { get; }
     }
 }

src/modules/peek/Peek.FilePreviewer/Previewers/MediaPreviewer/VideoPreviewer.cs

@@ -16,6 +16,8 @@
 using Peek.FilePreviewer.Previewers.Interfaces;
 using Windows.Foundation;
 using Windows.Media.Core;
+using Windows.Media.MediaProperties;
+using Windows.Media.Transcoding;
 using Windows.Storage;
 
 namespace Peek.FilePreviewer.Previewers
@@ -31,6 +33,9 @@ public partial class VideoPreviewer : ObservableObject, IVideoPreviewer, IDispos
         [ObservableProperty]
         private Size videoSize;
 
+        [ObservableProperty]
+        private string? errorMessage;
+
         public VideoPreviewer(IFileSystemItem file)
         {
             Item = file;
@@ -90,20 +95,98 @@ await Dispatcher.RunOnUiThread(async () =>
             });
         }
 
+        private async Task<bool> IsCodecSupportedAsync(StorageFile file)
+        {
+            try
+            {
+                // Create a MediaEncodingProfile from the file to check codec compatibility
+                var profile = await MediaEncodingProfile.CreateFromFileAsync(file);
+
+                // Use MediaTranscoder to check if the file can be transcoded (which indicates codec support)
+                var transcoder = new MediaTranscoder
+                {
+                    AlwaysReencode = false,
+                    HardwareAccelerationEnabled = true,
+                };
+
+                // We're not actually transcoding, just checking if we could
+                // Use the same profile as input and output for this test
+                var prepareResult = await transcoder.PrepareFileTranscodeAsync(file, file, profile);
+
+                // If we can't transcode with hardware acceleration, try without it
+                if (!prepareResult.CanTranscode && prepareResult.FailureReason == TranscodeFailureReason.HardwareNotAvailable)
+                {
+                    transcoder.HardwareAccelerationEnabled = false;
+                    prepareResult = await transcoder.PrepareFileTranscodeAsync(file, file, profile);
+                }
+
+                return prepareResult.CanTranscode;
+            }
+            catch (Exception)
+            {
+                // If the profile creation fails, we assume the codec is not supported
+                return false;
+            }
+        }
+
         private Task<bool> LoadVideoAsync(CancellationToken cancellationToken)
         {
             return TaskExtension.RunSafe(async () =>
             {
                 cancellationToken.ThrowIfCancellationRequested();
 
                 var storageFile = await Item.GetStorageItemAsync() as StorageFile;
-
-                await Dispatcher.RunOnUiThread(() =>
+                bool success = false;
+
+                // First, check if the codec is supported for this file
+                bool isCodecSupported = await IsCodecSupportedAsync(storageFile);
+
+                await Dispatcher.RunOnUiThread(async () =>
                 {
                     cancellationToken.ThrowIfCancellationRequested();
 
-                    Preview = MediaSource.CreateFromStorageFile(storageFile);
+                    try
+                    {
+                        if (!isCodecSupported)
+                        {
+                            // If codec is not supported, show error message immediately
+                            ErrorMessage = "This video requires codecs that are not installed on your system";
+                            success = false;
+                            return;
+                        }
+
+                        // For MP4 files, try CreateFromUri first as it provides better codec support
+                        // This helps with MP4 files that would otherwise only play audio without showing video
+                        if (Item.Extension.Equals(".mp4", StringComparison.OrdinalIgnoreCase))
+                        {
+                            try
+                            {
+                                var fileUri = new Uri(storageFile.Path);
+                                Preview = MediaSource.CreateFromUri(fileUri);
+                                success = true;
+                            }
+                            catch (Exception)
+                            {
+                                // If CreateFromUri fails, fall back to CreateFromStorageFile
+                                Preview = MediaSource.CreateFromStorageFile(storageFile);
+                                success = true;
+                            }
+                        }
+                        else
+                        {
+                            Preview = MediaSource.CreateFromStorageFile(storageFile);
+                            success = true;
+                        }
+                    }
+                    catch (Exception)
+                    {
+                        // If all methods fail, it's likely due to missing codecs
+                        ErrorMessage = "This video requires codecs that are not installed on your system";
+                        success = false;
+                    }
                 });
+
+                return success;
             });
         }