Add editor tool to create ping-pong videos from VideoClips via ffmpeg

Right-click a VideoClip -> Process -> Ping-Pong Video: runs ffmpeg in the
background (forward + reversed video concat, audio played twice), writes
<name>_pingpong.mp4 next to the source and imports it. Supports
multi-select, silent clips (video-only retry), progress display and
unique output paths.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Assets/Scripts/Editor/VideoPingPongProcessor.cs

@@ -0,0 +1,128 @@
+using System;
+using System.Diagnostics;
+using System.IO;
+using System.Text;
+using System.Threading;
+using UnityEditor;
+using UnityEngine.Video;
+using Debug = UnityEngine.Debug;
+
+namespace Chameleon.Editor
+{
+    /// <summary>
+    /// Right-click a VideoClip asset -> Process -> Ping-Pong Video.
+    /// Runs ffmpeg (from PATH) to append the reversed clip (first reversed frame
+    /// dropped to avoid a duplicate) and imports the result next to the original.
+    /// Audio is played twice in sequence, not reversed.
+    /// </summary>
+    public static class VideoPingPongProcessor
+    {
+        const string MenuPath = "Assets/Process/Ping-Pong Video";
+
+        const string VideoFilter =
+            "[0:v]split[v1][v2];[v2]reverse,trim=start_frame=1,setpts=PTS-STARTPTS[vr];" +
+            "[v1][vr]concat=n=2:v=1:a=0[vout]";
+
+        const string AudioFilter =
+            ";[0:a]asplit[a1][a2];[a1][a2]concat=n=2:v=0:a=1[aout]";
+
+        [MenuItem(MenuPath, true)]
+        static bool Validate()
+            => Selection.GetFiltered<VideoClip>(SelectionMode.Assets).Length > 0;
+
+        [MenuItem(MenuPath, false, 2000)]
+        static void Process()
+        {
+            var mainThread = SynchronizationContext.Current;
+            foreach (var clip in Selection.GetFiltered<VideoClip>(SelectionMode.Assets))
+                ProcessClip(clip, mainThread);
+        }
+
+        static void ProcessClip(VideoClip clip, SynchronizationContext mainThread)
+        {
+            string assetPath = AssetDatabase.GetAssetPath(clip);
+            if (string.IsNullOrEmpty(assetPath) || !File.Exists(assetPath))
+            {
+                Debug.LogError($"[PingPong] No source file for '{clip.name}'.");
+                return;
+            }
+
+            // Output is always .mp4 (libx264/aac), regardless of source container.
+            string directory = Path.GetDirectoryName(assetPath)?.Replace('\\', '/');
+            string outputAssetPath = AssetDatabase.GenerateUniqueAssetPath(
+                $"{directory}/{Path.GetFileNameWithoutExtension(assetPath)}_pingpong.mp4");
+
+            string inputFull = Path.GetFullPath(assetPath);
+            string outputFull = Path.GetFullPath(outputAssetPath);
+
+            int progressId = Progress.Start("Ping-Pong Video", Path.GetFileName(assetPath));
+
+            Run(inputFull, outputFull, withAudio: true, (success, log) =>
+            {
+                // Source without an audio stream: retry with video-only graph.
+                if (!success && log.Contains("matches no streams"))
+                {
+                    Run(inputFull, outputFull, withAudio: false,
+                        (retrySuccess, retryLog) => mainThread.Post(
+                            _ => Finish(retrySuccess, retryLog, outputAssetPath, outputFull, progressId), null));
+                    return;
+                }
+
+                mainThread.Post(_ => Finish(success, log, outputAssetPath, outputFull, progressId), null);
+            });
+        }
+
+        static void Run(string inputFull, string outputFull, bool withAudio, Action<bool, string> onDone)
+        {
+            string filter = withAudio ? VideoFilter + AudioFilter : VideoFilter;
+            string maps = withAudio ? "-map \"[vout]\" -map \"[aout]\" -c:v libx264 -c:a aac" : "-map \"[vout]\" -c:v libx264";
+
+            var startInfo = new ProcessStartInfo
+            {
+                FileName = "ffmpeg",
+                Arguments = $"-y -nostdin -i \"{inputFull}\" -filter_complex \"{filter}\" {maps} \"{outputFull}\"",
+                UseShellExecute = false,
+                CreateNoWindow = true,
+                RedirectStandardError = true,
+            };
+
+            var log = new StringBuilder();
+
+            try
+            {
+                var process = new Process { StartInfo = startInfo, EnableRaisingEvents = true };
+                process.ErrorDataReceived += (_, e) => { if (e.Data != null) log.AppendLine(e.Data); };
+                process.Exited += (_, _) =>
+                {
+                    bool success = process.ExitCode == 0;
+                    process.Dispose();
+                    onDone(success, log.ToString());
+                };
+                process.Start();
+                process.BeginErrorReadLine();
+            }
+            catch (Exception e)
+            {
+                onDone(false, $"Failed to start ffmpeg (not in PATH?): {e.Message}");
+            }
+        }
+
+        static void Finish(bool success, string log, string outputAssetPath, string outputFull, int progressId)
+        {
+            Progress.Remove(progressId);
+
+            if (!success)
+            {
+                if (File.Exists(outputFull))
+                    File.Delete(outputFull);
+                Debug.LogError($"[PingPong] ffmpeg failed for '{outputAssetPath}':\n{log}");
+                return;
+            }
+
+            AssetDatabase.ImportAsset(outputAssetPath);
+            var imported = AssetDatabase.LoadAssetAtPath<VideoClip>(outputAssetPath);
+            EditorGUIUtility.PingObject(imported);
+            Debug.Log($"[PingPong] Created '{outputAssetPath}'.", imported);
+        }
+    }
+}