chameleon/Assets/Scripts/Editor/VideoPingPongProcessor.cs

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);
        }
    }
}