Cancel ffmpeg

src/FFmpeg.NET/Extensions/ProcessExtensions.cs

@@ -1,33 +1,58 @@
-using System;
-using System.Diagnostics;
-using System.Threading;
-using System.Threading.Tasks;
-
-namespace FFmpeg.NET.Extensions
-{
-    public static class ProcessExtensions
-    {
-        public static Task<int> WaitForExitAsync(this Process process, Action<int> onException, CancellationToken cancellationToken = default)
-        {
-            var tcs = new TaskCompletionSource<int>();
-            if (cancellationToken != default)
-                cancellationToken.Register(tcs.SetCanceled);
-
-            process.EnableRaisingEvents = true;
-            process.Exited += (sender, e) =>
-            {
-                if (process.ExitCode != 0)
-                    onException?.Invoke(process.ExitCode);
-                tcs.TrySetResult(process.ExitCode);
-            };
-
-            var started = process.Start();
-            if (!started)
-                tcs.TrySetException(new InvalidOperationException($"Could not start process {process}"));
-
-            process.BeginErrorReadLine();
-
-            return tcs.Task;
-        }
-    }
-}
+using System;
+using System.Diagnostics;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace FFmpeg.NET.Extensions
+{
+    public static class ProcessExtensions
+    {
+        public static Task<int> WaitForExitAsync(this Process process, Action<int> onException, CancellationToken cancellationToken = default)
+        {
+            TaskCompletionSource<int> tcs = new TaskCompletionSource<int>();
+            if (cancellationToken != default)
+            {
+                cancellationToken.Register(() =>
+                {
+                    try
+                    {
+                        // Send "q" to ffmpeg, which will force it to stop (closing files).
+                        process.StandardInput.Write("q");
+                    }
+                    catch (InvalidOperationException)
+                    {
+                        // If the process doesn't exist anymore, ignore it.
+                    }
+                    finally
+                    {
+                        // Cancel the task. This will throw an exception to the calling program.
+                        // Exc.Message will be "A task was canceled."
+                        try
+                        {
+                            tcs.SetCanceled();
+                        }
+                        catch (Exception)
+                        {
+                        }
+                    }
+                });
+            }
+
+            process.EnableRaisingEvents = true;
+            process.Exited += (sender, e) =>
+            {
+                if (process.ExitCode != 0)
+                    onException?.Invoke(process.ExitCode);
+                tcs.TrySetResult(process.ExitCode);
+            };
+
+            var started = process.Start();
+            if (!started)
+                tcs.TrySetException(new InvalidOperationException($"Could not start process {process}"));
+
+            process.BeginErrorReadLine();
+
+            return tcs.Task;
+        }
+    }
+}

src/FFmpeg.NET/FFmpegProcess.cs

@@ -29,8 +29,24 @@ private async Task ExecuteAsync(ProcessStartInfo startInfo, FFmpegParameters par
                 ffmpegProcess.ErrorDataReceived += (sender, e) => OnData(new ConversionDataEventArgs(e.Data, parameters.InputFile, parameters.OutputFile));
                 ffmpegProcess.ErrorDataReceived += (sender, e) => FFmpegProcessOnErrorDataReceived(e, parameters, ref caughtException, messages);
 
-                await ffmpegProcess.WaitForExitAsync((exitCode) => OnException(messages, parameters, exitCode, caughtException), cancellationToken);
-
+                Task<int> task = null;
+                try
+                {
+                    task = ffmpegProcess.WaitForExitAsync((exitCode) => OnException(messages, parameters, exitCode, caughtException), cancellationToken);
+                    await task;
+                }
+                catch (Exception)
+                {
+                    // An exception occurs if the user cancels the operation by calling Cancel on the CancellationToken.
+                    // Exc.Message will be "A task was canceled." (in English).
+                    // task.IsCanceled will be true.
+                    if (task.IsCanceled)
+                    {
+                        throw new TaskCanceledException(task);
+                    }
+                    // I don't think this can occur, but if some other exception, rethrow it.
+                    throw;
+                }
                 if (caughtException != null || ffmpegProcess.ExitCode != 0)
                 {
                     OnException(messages, parameters, ffmpegProcess.ExitCode, caughtException);
@@ -49,7 +65,7 @@ private void OnException(List<string> messages, FFmpegParameters parameters, int
             OnConversionError(new ConversionErrorEventArgs(exception, parameters.InputFile, parameters.OutputFile));
         }
 
-        private string GetExceptionMessage(List<string> messages) 
+        private string GetExceptionMessage(List<string> messages)
             => messages.Count > 1
                 ? messages[1] + messages[0]
                 : string.Join(string.Empty, messages);
@@ -93,10 +109,11 @@ private void FFmpegProcessOnErrorDataReceived(DataReceivedEventArgs e, FFmpegPar
 
         private ProcessStartInfo GenerateStartInfo(string ffmpegPath, string arguments) => new ProcessStartInfo
         {
-            Arguments = "-nostdin -y -loglevel info " + arguments,
+            // -y overwrite output files
+            Arguments = "-y " + arguments,
             FileName = ffmpegPath,
             CreateNoWindow = true,
-            RedirectStandardInput = false,
+            RedirectStandardInput = true,
             RedirectStandardOutput = true,
             RedirectStandardError = true,
             UseShellExecute = false,
@@ -116,4 +133,4 @@ private void FFmpegProcessOnErrorDataReceived(DataReceivedEventArgs e, FFmpegPar
 
         private void OnData(ConversionDataEventArgs eventArgs) => Data?.Invoke(eventArgs);
     }
-}
+}