Add video preview, source crop, find-videos, and render toasts

Bring the Video tab closer to Shorts with 4K preview stills and crop
modes (none, auto, center, plus the visual editor). Settings store a
default source folder so Find videos can collect output.avi sequences.
Cap the FFmpeg log with auto-scroll, hide repeat spam, and show a
Windows notification when a video or short finishes or fails.

Services/ShortsPipeline.cs

@@ -1,7 +1,6 @@
 using System.Globalization;
 using System.IO;
 using System.Text;
-using System.Text.RegularExpressions;
 using AmiReel.Models;
 
 namespace AmiReel.Services;
@@ -13,12 +12,7 @@ namespace AmiReel.Services;
 /// </summary>
 public sealed class ShortsPipeline
 {
-    internal const string DefaultSourceCropFilter =
-        "crop='min(iw,ih*4/3)':'min(ih,iw*3/4)':'(iw-ow)/2':'(ih-oh)/2'";
-
-    private static readonly Regex CropSpecRegex = new(
-        @"crop=(\d+):(\d+):(\d+):(\d+)",
-        RegexOptions.CultureInvariant);
+    internal const string DefaultSourceCropFilter = SourceCropFilters.CenterFourByThreeFilter;
 
     private readonly ProcessRunner _runner = new();
 
@@ -421,7 +415,7 @@ public sealed class ShortsPipeline
         $"scale={SourceTargetWidth(sourceMarginX)}:-2:flags=lanczos";
 
     internal static string BuildManualCropFilter(int left, int right, int top, int bottom) =>
-        $"crop=iw-{left}-{right}:ih-{top}-{bottom}:{left}:{top}";
+        SourceCropFilters.BuildManualCropFilter(left, right, top, bottom);
 
     internal static string BuildVideoBaseFilter(string cropFilter, string scaleFilter, double blur, double opacity)
     {
@@ -430,49 +424,18 @@ public sealed class ShortsPipeline
             "color=c=black:s=1080x1920:r=50[black];" +
             $"[1:v]scale=1080:1920:force_original_aspect_ratio=increase,crop=1080:1920,setsar=1{blurFilter},format=rgba,colorchannelmixer=aa={F(opacity)}[bgvideo];" +
             "[black][bgvideo]overlay=x=0:y=0:format=auto[bg];" +
-            $"[0:v]{cropFilter},{scaleFilter},setsar=1[fg];" +
+            $"[0:v]{SourceCropFilters.Prefix(cropFilter, scaleFilter)},setsar=1[fg];" +
             "[bg][fg]overlay=x=(W-w)/2:y=(H-h)/2:format=auto[base]";
     }
 
-    internal static string? SelectMostCommonCropSpec(string ffmpegOutput)
-    {
-        Dictionary<string, int> counts = new(StringComparer.Ordinal);
-        foreach (Match match in CropSpecRegex.Matches(ffmpegOutput))
-        {
-            string spec = match.Value;
-            counts[spec] = counts.GetValueOrDefault(spec) + 1;
-        }
+    internal static string? SelectMostCommonCropSpec(string ffmpegOutput) =>
+        SourceCropFilters.SelectMostCommonCropSpec(ffmpegOutput);
 
-        return counts.Count == 0
-            ? null
-            : counts.OrderByDescending(pair => pair.Value).ThenBy(pair => pair.Key, StringComparer.Ordinal).First().Key;
-    }
+    internal static bool TryParseCropSpec(string spec, out int width, out int height, out int x, out int y) =>
+        SourceCropFilters.TryParseCropSpec(spec, out width, out height, out x, out y);
 
-    internal static bool TryParseCropSpec(string spec, out int width, out int height, out int x, out int y)
-    {
-        Match match = CropSpecRegex.Match(spec);
-        if (!match.Success)
-        {
-            width = height = x = y = 0;
-            return false;
-        }
-
-        width = int.Parse(match.Groups[1].Value, CultureInfo.InvariantCulture);
-        height = int.Parse(match.Groups[2].Value, CultureInfo.InvariantCulture);
-        x = int.Parse(match.Groups[3].Value, CultureInfo.InvariantCulture);
-        y = int.Parse(match.Groups[4].Value, CultureInfo.InvariantCulture);
-        return true;
-    }
-
-    internal static bool TryBuildAutoHorizontalCrop(int detectedWidth, int detectedX, out int width, out int x)
-    {
-        int inset = (int)(detectedWidth * 0.005 / 2) * 2;
-        width = ((detectedWidth - (2 * inset)) / 2) * 2;
-        x = ((detectedX + inset) / 2) * 2;
-        if (width < 16)
-            return false;
-        return true;
-    }
+    internal static bool TryBuildAutoHorizontalCrop(int detectedWidth, int detectedX, out int width, out int x) =>
+        SourceCropFilters.TryBuildAutoHorizontalCrop(detectedWidth, detectedX, out width, out x);
 
     private async Task<string> ResolveBaseFilterAsync(
         ToolPaths tools, ShortSettings settings, Action<string> log, CancellationToken token)
@@ -480,33 +443,36 @@ public sealed class ShortsPipeline
         if (settings.Style != ShortStyle.Video)
             return GetBaseFilter(settings.Style);
 
-        string cropFilter = DefaultSourceCropFilter;
         string scaleFilter = BuildSourceScaleFilter(settings.SourceMarginX);
-        bool hasManualCrop = settings.CropLeft > 0 || settings.CropRight > 0
-            || settings.CropTop > 0 || settings.CropBottom > 0;
-
-        if (hasManualCrop)
+        string? detected = null;
+        if (!SourceCropFilters.HasManualCrop(settings.CropLeft, settings.CropRight, settings.CropTop, settings.CropBottom)
+            && settings.SourceCropMode == ShortSourceCropMode.Auto)
+        {
+            detected = await DetectHorizontalCropAsync(tools, settings, log, token);
+            if (detected is null)
+                log("Warning: could not auto-detect left/right source black borders; using centered 4:3 crop.");
+        }
+        else if (SourceCropFilters.HasManualCrop(settings.CropLeft, settings.CropRight, settings.CropTop, settings.CropBottom))
         {
-            cropFilter = BuildManualCropFilter(settings.CropLeft, settings.CropRight, settings.CropTop, settings.CropBottom);
             log($"Source crop: manual L={settings.CropLeft} R={settings.CropRight} T={settings.CropTop} B={settings.CropBottom}");
         }
-        else if (settings.SourceCropMode == ShortSourceCropMode.Auto)
+        else if (settings.SourceCropMode == ShortSourceCropMode.None)
         {
-            string? detected = await DetectHorizontalCropAsync(tools, settings, log, token);
-            if (detected is not null)
-            {
-                cropFilter = detected;
-            }
-            else
-            {
-                log("Warning: could not auto-detect left/right source black borders; using centered 4:3 crop.");
-            }
+            log("Source crop: none");
         }
         else
         {
             log("Source crop: centered 4:3");
         }
 
+        string cropFilter = SourceCropFilters.Resolve(
+            settings.SourceCropMode,
+            settings.CropLeft,
+            settings.CropRight,
+            settings.CropTop,
+            settings.CropBottom,
+            detected);
+
         return BuildVideoBaseFilter(cropFilter, scaleFilter, settings.VideoBlur, settings.VideoOpacity);
     }
 
@@ -514,27 +480,16 @@ public sealed class ShortsPipeline
         ToolPaths tools, ShortSettings settings, Action<string> log, CancellationToken token)
     {
         double detectDuration = Math.Clamp(settings.DurationSeconds < 4 ? settings.DurationSeconds : 4, 0.5, 4);
-        List<string> args =
-        [
-            "-hide_banner",
-            "-ss", settings.Start,
-            "-t", F(detectDuration),
-            "-i", settings.InputFile,
-            "-an",
-            "-vf", "crop=iw:trunc(ih*0.70/2)*2:0:trunc(ih*0.15/2)*2,cropdetect=limit=28:round=2:reset=0",
-            "-f", "null",
-            "-",
-        ];
+        List<string> args = SourceCropFilters.BuildHorizontalCropDetectArguments(
+            settings.InputFile, settings.Start, detectDuration);
 
         string output = await _runner.RunAsync(tools.Ffmpeg, args, log, null, token, allowFailure: true);
-        string? spec = SelectMostCommonCropSpec(output);
-        if (spec is null || !TryParseCropSpec(spec, out int width, out _, out int x, out _))
-            return null;
-        if (!TryBuildAutoHorizontalCrop(width, x, out int cropWidth, out int cropX))
+        string? filter = SourceCropFilters.TryBuildAutoHorizontalFilter(output);
+        if (filter is null)
             return null;
 
-        log($"Source crop: w={cropWidth}, x={cropX} (auto left/right black crop)");
-        return $"crop={cropWidth}:ih:{cropX}:0";
+        log($"Source crop: {filter} (auto left/right black crop)");
+        return filter;
     }
 
     internal static string GetBaseFilter(ShortStyle style) => style switch