[Bug] Crashing frequently when importing an mp4

[Sasani-Likes-Penguins]

When I try opening an mp4 with ffmpeg or Media Player the app crashes around 90% of the time. It does the same while saving a gif as well. Sometimes it disappears without an error, but this is the one I get:

DialogResult can be set only after Window is created and shown as dialog.

at System.Windows.Window.set_DialogResult(Nullable`1 value)
at ScreenToGif.Windows.Other.VideoSource.<Window_Loaded>b__10_5() in R:\Source\ScreenToGif\ScreenToGif\Windows\Other\VideoSource.xaml.cs:line 88
at System.Windows.Threading.DispatcherOperation.InvokeDelegateCore()
at System.Windows.Threading.DispatcherOperation.InvokeImpl()
--- End of stack trace from previous location ---
at System.Windows.Threading.DispatcherOperation.Wait(TimeSpan timeout)
at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherOperation operation, CancellationToken cancellationToken, TimeSpan timeout)
at System.Windows.Threading.Dispatcher.Invoke(Action callback, DispatcherPriority priority, CancellationToken cancellationToken, TimeSpan timeout)
at System.Windows.Threading.Dispatcher.Invoke(Action callback)
at ScreenToGif.Windows.Other.VideoSource.<Window_Loaded>b__10_3(Object _, EventArgs _) in R:\Source\ScreenToGif\ScreenToGif\Windows\Other\VideoSource.xaml.cs:line 85
at ScreenToGif.ViewModel.VideoSourceViewModel.GetFiles(String folder) in R:\Source\ScreenToGif\ScreenToGif.ViewModel\VideoSourceViewModel.cs:line 827
at ScreenToGif.ViewModel.VideoSourceViewModel.<>c__DisplayClass124_0.b__1(Object sender, DataReceivedEventArgs e) in R:\Source\ScreenToGif\ScreenToGif.ViewModel\VideoSourceViewModel.cs:line 736
at System.Diagnostics.AsyncStreamReader.FlushMessageQueue(Boolean rethrowInNewThread)
--- End of stack trace from previous location ---
at System.Threading.QueueUserWorkItemCallback.Execute()
at System.Threading.ThreadPoolWorkQueue.Dispatch()
at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart()