From 4e586c73e9f250e44ca10b3e5589cc3bebba8c85 Mon Sep 17 00:00:00 2001
From: niksedk <nikse.dk@gmail.com>
Date: Sun, 17 May 2026 15:17:55 +0200
Subject: [PATCH] Add Typewriter effect SE5 plugin (Avalonia)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Ports the SE4 "Effect → Typewriter…" feature (issue #10942) as a
standalone SE5 plugin. Each selected subtitle line is exploded into
several short lines that progressively reveal the text character by
character, with an optional end delay holding the fully-typed line
before the original end time.

The plugin is an Avalonia 11 / .NET 8 app:
- Settings dialog with a numeric input for the end delay.
- Inherits Dark/Light theme from request.theme.
- Persists endDelay via the plugin Settings round-trip.
- Inline SRT parser/serializer; ASSA overrides and html i/b/u/font
  tags are preserved across the exploded paragraphs.

Adds .github/workflows/typewriter.yml that mirrors haxor.yml:
matrix self-contained publish for the six supported RIDs, plugin.json
rewritten to per-OS executables block per zip, and (on dispatch with
a tag) a GitHub release with all six zips attached. Updates
se5-plugins.json to point at the planned se5-typewriter-v1.0 release
assets via the per-platform downloads map.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 .github/workflows/typewriter.yml             | 107 +++++++++
 se5-plugins.json                             |  17 ++
 se5/TypewriterEffect/App.axaml               |   8 +
 se5/TypewriterEffect/App.axaml.cs            |  34 +++
 se5/TypewriterEffect/MainWindow.axaml        |  54 +++++
 se5/TypewriterEffect/MainWindow.axaml.cs     |  90 ++++++++
 se5/TypewriterEffect/PluginContract.cs       |  40 ++++
 se5/TypewriterEffect/Program.cs              |  63 ++++++
 se5/TypewriterEffect/README.md               |  37 ++++
 se5/TypewriterEffect/SubRipParser.cs         |  88 ++++++++
 se5/TypewriterEffect/TypewriterEffect.csproj |  22 ++
 se5/TypewriterEffect/TypewriterEngine.cs     | 219 +++++++++++++++++++
 se5/TypewriterEffect/app.manifest            |  10 +
 se5/TypewriterEffect/plugin.json             |  12 +
 14 files changed, 801 insertions(+)
 create mode 100644 .github/workflows/typewriter.yml
 create mode 100644 se5/TypewriterEffect/App.axaml
 create mode 100644 se5/TypewriterEffect/App.axaml.cs
 create mode 100644 se5/TypewriterEffect/MainWindow.axaml
 create mode 100644 se5/TypewriterEffect/MainWindow.axaml.cs
 create mode 100644 se5/TypewriterEffect/PluginContract.cs
 create mode 100644 se5/TypewriterEffect/Program.cs
 create mode 100644 se5/TypewriterEffect/README.md
 create mode 100644 se5/TypewriterEffect/SubRipParser.cs
 create mode 100644 se5/TypewriterEffect/TypewriterEffect.csproj
 create mode 100644 se5/TypewriterEffect/TypewriterEngine.cs
 create mode 100644 se5/TypewriterEffect/app.manifest
 create mode 100644 se5/TypewriterEffect/plugin.json

diff --git a/.github/workflows/typewriter.yml b/.github/workflows/typewriter.yml
new file mode 100644
index 0000000..7aca494
--- /dev/null
+++ b/.github/workflows/typewriter.yml
@@ -0,0 +1,107 @@
+name: Build TypewriterEffect (SE5)
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'se5/TypewriterEffect/**'
+      - '.github/workflows/typewriter.yml'
+  pull_request:
+    paths:
+      - 'se5/TypewriterEffect/**'
+      - '.github/workflows/typewriter.yml'
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: 'Release tag to publish the zips under (e.g. se5-typewriter-v1.0). Leave empty to build artifacts only.'
+        required: false
+        type: string
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - rid: win-x64
+            os: windows
+            exe: TypewriterEffect.exe
+          - rid: win-arm64
+            os: windows
+            exe: TypewriterEffect.exe
+          - rid: linux-x64
+            os: linux
+            exe: TypewriterEffect
+          - rid: linux-arm64
+            os: linux
+            exe: TypewriterEffect
+          - rid: osx-x64
+            os: macos
+            exe: TypewriterEffect
+          - rid: osx-arm64
+            os: macos
+            exe: TypewriterEffect
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup .NET 8
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '8.0.x'
+
+      - name: Publish self-contained (${{ matrix.rid }})
+        working-directory: se5/TypewriterEffect
+        run: |
+          dotnet publish TypewriterEffect.csproj \
+            -c Release \
+            -r ${{ matrix.rid }} \
+            --self-contained true \
+            -p:PublishSingleFile=true \
+            -p:IncludeNativeLibrariesForSelfExtract=true \
+            -o staging/TypewriterEffect
+
+      - name: Rewrite plugin.json for ${{ matrix.os }}
+        working-directory: se5/TypewriterEffect
+        run: |
+          jq '
+            del(.runtime, .entry) |
+            .executables = { "${{ matrix.os }}": "${{ matrix.exe }}" }
+          ' plugin.json > staging/TypewriterEffect/plugin.json
+
+      - name: Package zip
+        working-directory: se5/TypewriterEffect/staging
+        run: zip -r "$GITHUB_WORKSPACE/TypewriterEffect-${{ matrix.rid }}.zip" TypewriterEffect
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: TypewriterEffect-${{ matrix.rid }}
+          path: TypewriterEffect-${{ matrix.rid }}.zip
+
+  release:
+    name: Publish GitHub Release
+    needs: build
+    if: github.event_name == 'workflow_dispatch' && github.event.inputs.tag != ''
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - name: Download all zips
+        uses: actions/download-artifact@v4
+        with:
+          path: dist
+          pattern: TypewriterEffect-*
+          merge-multiple: true
+
+      - name: Create release and upload zips
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh release create "${{ github.event.inputs.tag }}" dist/TypewriterEffect-*.zip \
+            --repo "${{ github.repository }}" \
+            --target "${{ github.sha }}" \
+            --title "TypewriterEffect ${{ github.event.inputs.tag }}" \
+            --notes "Self-contained TypewriterEffect plugin builds for win/linux/osx (x64 + arm64)."
diff --git a/se5-plugins.json b/se5-plugins.json
index ae76ba2..add5a84 100644
--- a/se5-plugins.json
+++ b/se5-plugins.json
@@ -1,5 +1,22 @@
 {
   "plugins": [
+    {
+      "name": "Typewriter effect",
+      "description": "Splits each subtitle line into short timed parts that progressively reveal the text, character by character.",
+      "version": "1.0.0",
+      "author": "Subtitle Edit",
+      "url": "https://github.com/SubtitleEdit/plugins/tree/main/se5/TypewriterEffect",
+      "date": "2026-05-17",
+      "minSeVersion": "5.0.0",
+      "downloads": {
+        "win-x64":     "https://github.com/SubtitleEdit/plugins/releases/download/se5-typewriter-v1.0/TypewriterEffect-win-x64.zip",
+        "win-arm64":   "https://github.com/SubtitleEdit/plugins/releases/download/se5-typewriter-v1.0/TypewriterEffect-win-arm64.zip",
+        "linux-x64":   "https://github.com/SubtitleEdit/plugins/releases/download/se5-typewriter-v1.0/TypewriterEffect-linux-x64.zip",
+        "linux-arm64": "https://github.com/SubtitleEdit/plugins/releases/download/se5-typewriter-v1.0/TypewriterEffect-linux-arm64.zip",
+        "osx-x64":     "https://github.com/SubtitleEdit/plugins/releases/download/se5-typewriter-v1.0/TypewriterEffect-osx-x64.zip",
+        "osx-arm64":   "https://github.com/SubtitleEdit/plugins/releases/download/se5-typewriter-v1.0/TypewriterEffect-osx-arm64.zip"
+      }
+    },
     {
       "name": "Haxor",
       "description": "Translates the text of the selected lines (or all lines) to haxor.",
diff --git a/se5/TypewriterEffect/App.axaml b/se5/TypewriterEffect/App.axaml
new file mode 100644
index 0000000..c802d73
--- /dev/null
+++ b/se5/TypewriterEffect/App.axaml
@@ -0,0 +1,8 @@
+<Application xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="SubtitleEdit.Plugins.TypewriterEffect.App"
+             RequestedThemeVariant="Default">
+    <Application.Styles>
+        <FluentTheme />
+    </Application.Styles>
+</Application>
diff --git a/se5/TypewriterEffect/App.axaml.cs b/se5/TypewriterEffect/App.axaml.cs
new file mode 100644
index 0000000..6e1699b
--- /dev/null
+++ b/se5/TypewriterEffect/App.axaml.cs
@@ -0,0 +1,34 @@
+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Markup.Xaml;
+using Avalonia.Styling;
+
+namespace SubtitleEdit.Plugins.TypewriterEffect;
+
+public partial class App : Application
+{
+    /// <summary>Set by Program.Main before Avalonia starts.</summary>
+    public static PluginRequest? PendingRequest;
+
+    /// <summary>Filled in by MainWindow when the user clicks OK or Cancel.</summary>
+    public static PluginResponse? Response;
+
+    public override void Initialize() => AvaloniaXamlLoader.Load(this);
+
+    public override void OnFrameworkInitializationCompleted()
+    {
+        if (PendingRequest is not null)
+        {
+            RequestedThemeVariant = string.Equals(PendingRequest.Theme, "Dark", System.StringComparison.OrdinalIgnoreCase)
+                ? ThemeVariant.Dark
+                : ThemeVariant.Light;
+
+            if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+            {
+                desktop.MainWindow = new MainWindow(PendingRequest);
+            }
+        }
+
+        base.OnFrameworkInitializationCompleted();
+    }
+}
diff --git a/se5/TypewriterEffect/MainWindow.axaml b/se5/TypewriterEffect/MainWindow.axaml
new file mode 100644
index 0000000..bfc130c
--- /dev/null
+++ b/se5/TypewriterEffect/MainWindow.axaml
@@ -0,0 +1,54 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        mc:Ignorable="d"
+        x:Class="SubtitleEdit.Plugins.TypewriterEffect.MainWindow"
+        Title="Typewriter effect"
+        Width="520" Height="360"
+        WindowStartupLocation="CenterScreen"
+        CanResize="False">
+    <DockPanel Margin="20">
+        <StackPanel DockPanel.Dock="Bottom"
+                    Orientation="Horizontal"
+                    HorizontalAlignment="Right"
+                    Spacing="10"
+                    Margin="0,16,0,0">
+            <Button Content="Cancel"
+                    Click="OnCancel"
+                    MinWidth="100" />
+            <Button x:Name="OkButton"
+                    Content="OK"
+                    Click="OnOk"
+                    MinWidth="100"
+                    Classes="accent"
+                    IsDefault="True" />
+        </StackPanel>
+
+        <StackPanel Orientation="Vertical" Spacing="14">
+            <TextBlock FontSize="18"
+                       FontWeight="SemiBold"
+                       Text="Typewriter effect" />
+
+            <TextBlock x:Name="InfoLabel"
+                       Opacity="0.8"
+                       TextWrapping="Wrap" />
+
+            <StackPanel Orientation="Vertical" Spacing="6">
+                <TextBlock Text="End delay (seconds)" />
+                <NumericUpDown x:Name="EndDelayInput"
+                               Minimum="0"
+                               Maximum="10"
+                               Increment="0.5"
+                               FormatString="0.0##"
+                               Value="0.5"
+                               Width="160"
+                               HorizontalAlignment="Left" />
+                <TextBlock Opacity="0.65"
+                           FontSize="11"
+                           TextWrapping="Wrap"
+                           Text="After the last character appears, the full line stays on screen for this long before the original end time." />
+            </StackPanel>
+        </StackPanel>
+    </DockPanel>
+</Window>
diff --git a/se5/TypewriterEffect/MainWindow.axaml.cs b/se5/TypewriterEffect/MainWindow.axaml.cs
new file mode 100644
index 0000000..270738a
--- /dev/null
+++ b/se5/TypewriterEffect/MainWindow.axaml.cs
@@ -0,0 +1,90 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Markup.Xaml;
+using System;
+using System.Text.Json;
+
+namespace SubtitleEdit.Plugins.TypewriterEffect;
+
+public partial class MainWindow : Window
+{
+    private readonly PluginRequest _request;
+
+    // Parameterless constructor only exists for the XAML designer.
+    public MainWindow() : this(new PluginRequest()) { }
+
+    public MainWindow(PluginRequest request)
+    {
+        InitializeComponent();
+        _request = request;
+
+        var selectedCount = request.SelectedIndices.Count;
+        InfoLabel.Text = selectedCount > 0
+            ? $"Each of the {selectedCount} selected line(s) will be split into several short lines that progressively reveal the text."
+            : "Every line will be split into several short lines that progressively reveal the text.";
+
+        EndDelayInput.Value = (decimal)LoadEndDelaySetting(request.Settings, defaultValue: 0.5);
+    }
+
+    private void InitializeComponent() => AvaloniaXamlLoader.Load(this);
+
+    private void OnCancel(object? sender, RoutedEventArgs e)
+    {
+        App.Response = new PluginResponse { Status = "cancelled" };
+        Close();
+    }
+
+    private void OnOk(object? sender, RoutedEventArgs e)
+    {
+        var endDelaySec = (double)(EndDelayInput.Value ?? 0m);
+
+        try
+        {
+            var blocks = SubRipParser.Parse(_request.Subtitle.SubRip);
+            var selected = new HashSet<int>(_request.SelectedIndices);
+            var (resultBlocks, changed) = TypewriterEngine.Apply(blocks, selected, endDelaySec);
+
+            App.Response = new PluginResponse
+            {
+                Status = "ok",
+                Message = changed == 0
+                    ? "No lines changed."
+                    : $"Typewriter applied to {changed} line(s).",
+                UndoDescription = "Typewriter effect",
+                Subtitle = new PluginSubtitle
+                {
+                    Format = "SubRip",
+                    Native = SubRipParser.Serialize(resultBlocks),
+                },
+                Settings = BuildSettings(endDelaySec),
+            };
+        }
+        catch (Exception ex)
+        {
+            App.Response = new PluginResponse { Status = "error", Message = ex.Message };
+        }
+
+        Close();
+    }
+
+    private static double LoadEndDelaySetting(JsonElement? settings, double defaultValue)
+    {
+        if (settings is null || settings.Value.ValueKind != JsonValueKind.Object)
+        {
+            return defaultValue;
+        }
+        if (settings.Value.TryGetProperty("endDelay", out var value) &&
+            value.ValueKind == JsonValueKind.Number &&
+            value.TryGetDouble(out var parsed))
+        {
+            return parsed;
+        }
+        return defaultValue;
+    }
+
+    private static JsonElement BuildSettings(double endDelay)
+    {
+        using var doc = JsonDocument.Parse($"{{\"endDelay\":{endDelay.ToString("0.###", System.Globalization.CultureInfo.InvariantCulture)}}}");
+        return doc.RootElement.Clone();
+    }
+}
diff --git a/se5/TypewriterEffect/PluginContract.cs b/se5/TypewriterEffect/PluginContract.cs
new file mode 100644
index 0000000..5c1e16e
--- /dev/null
+++ b/se5/TypewriterEffect/PluginContract.cs
@@ -0,0 +1,40 @@
+using System.Text.Json;
+
+namespace SubtitleEdit.Plugins.TypewriterEffect;
+
+// Mirrors the Subtitle Edit 5 plugin JSON contract.
+// See https://github.com/SubtitleEdit/subtitleedit/blob/main/docs/plugin.md
+
+public sealed class PluginRequest
+{
+    public int ApiVersion { get; set; } = 1;
+    public string RequestType { get; set; } = "run";
+    public string ResponseFilePath { get; set; } = string.Empty;
+    public string TempDirectory { get; set; } = string.Empty;
+    public PluginSubtitle Subtitle { get; set; } = new();
+    public List<int> SelectedIndices { get; set; } = new();
+    public string VideoFileName { get; set; } = string.Empty;
+    public double FrameRate { get; set; }
+    public string UiLanguage { get; set; } = string.Empty;
+    public string Theme { get; set; } = string.Empty;
+    public string SeVersion { get; set; } = string.Empty;
+    public JsonElement? Settings { get; set; }
+}
+
+public sealed class PluginSubtitle
+{
+    public string Format { get; set; } = string.Empty;
+    public string FileName { get; set; } = string.Empty;
+    public string Native { get; set; } = string.Empty;
+    public string SubRip { get; set; } = string.Empty;
+}
+
+public sealed class PluginResponse
+{
+    public int ApiVersion { get; set; } = 1;
+    public string Status { get; set; } = "cancelled";
+    public string? Message { get; set; }
+    public PluginSubtitle? Subtitle { get; set; }
+    public JsonElement? Settings { get; set; }
+    public string? UndoDescription { get; set; }
+}
diff --git a/se5/TypewriterEffect/Program.cs b/se5/TypewriterEffect/Program.cs
new file mode 100644
index 0000000..b307493
--- /dev/null
+++ b/se5/TypewriterEffect/Program.cs
@@ -0,0 +1,63 @@
+using Avalonia;
+using System;
+using System.IO;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace SubtitleEdit.Plugins.TypewriterEffect;
+
+// A Subtitle Edit 5 plugin is just an executable:
+//   1. read the request file (its path is the first command-line argument),
+//   2. show the Avalonia window,
+//   3. write the response file (path is given in the request),
+//   4. exit with code 0.
+public static class Program
+{
+    private static readonly JsonSerializerOptions JsonOpts = new()
+    {
+        PropertyNameCaseInsensitive = true,
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+        WriteIndented = true,
+    };
+
+    [STAThread]
+    public static int Main(string[] args)
+    {
+        if (args.Length < 1)
+        {
+            Console.Error.WriteLine("Usage: TypewriterEffect <requestFilePath>");
+            return 1;
+        }
+
+        PluginRequest? request;
+        try
+        {
+            request = JsonSerializer.Deserialize<PluginRequest>(File.ReadAllText(args[0]), JsonOpts);
+        }
+        catch (Exception exception)
+        {
+            Console.Error.WriteLine("Could not read request: " + exception.Message);
+            return 1;
+        }
+
+        if (request is null || string.IsNullOrEmpty(request.ResponseFilePath))
+        {
+            Console.Error.WriteLine("Invalid request.");
+            return 1;
+        }
+
+        App.PendingRequest = request;
+        BuildAvaloniaApp().StartWithClassicDesktopLifetime(Array.Empty<string>());
+
+        var response = App.Response ?? new PluginResponse { Status = "cancelled" };
+        File.WriteAllText(request.ResponseFilePath, JsonSerializer.Serialize(response, JsonOpts));
+        return 0;
+    }
+
+    public static AppBuilder BuildAvaloniaApp() =>
+        AppBuilder.Configure<App>()
+            .UsePlatformDetect()
+            .WithInterFont()
+            .LogToTrace();
+}
diff --git a/se5/TypewriterEffect/README.md b/se5/TypewriterEffect/README.md
new file mode 100644
index 0000000..7dbe92c
--- /dev/null
+++ b/se5/TypewriterEffect/README.md
@@ -0,0 +1,37 @@
+# Typewriter effect (Subtitle Edit 5 plugin)
+
+Splits each selected subtitle line into a sequence of short, timed lines that
+progressively reveal the text — character by character — over the same on-screen
+duration. Optionally holds the fully-typed line for an *end delay* before the
+original end time.
+
+Ported from the SE4 *Effect → Typewriter…* dialog, repackaged as a standalone
+Avalonia 11 desktop app that communicates with Subtitle Edit through the
+[SE5 plugin JSON contract](https://github.com/SubtitleEdit/subtitleedit/blob/main/docs/plugin.md).
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `plugin.json` | Manifest. Currently uses `runtime: dotnet` (the build workflow rewrites it to per-platform `executables` for release zips). |
+| `PluginContract.cs` | Request/response DTOs (the JSON contract). |
+| `Program.cs` | Reads the request, boots Avalonia, writes the response. |
+| `App.axaml(.cs)` | Avalonia application. Picks `Dark` or `Light` theme variant based on `request.theme`. |
+| `MainWindow.axaml(.cs)` | The settings dialog (end-delay numeric input + OK/Cancel). |
+| `SubRipParser.cs` | Minimal SRT parser/serializer. |
+| `TypewriterEngine.cs` | Generates the exploded paragraphs from the original ones. |
+
+## Build (local)
+
+```
+dotnet publish TypewriterEffect.csproj -c Release -r <rid> --self-contained -o publish
+```
+
+## CI builds
+
+`.github/workflows/typewriter.yml` does a matrix self-contained publish for the
+six supported RIDs (`win-x64`, `win-arm64`, `linux-x64`, `linux-arm64`,
+`osx-x64`, `osx-arm64`), rewrites `plugin.json` to use the per-OS `executables`
+block, and (on manual dispatch with a tag) attaches all six zips to a GitHub
+release. The `se5-plugins.json` index then points at the release URLs via its
+per-platform `downloads` map.
diff --git a/se5/TypewriterEffect/SubRipParser.cs b/se5/TypewriterEffect/SubRipParser.cs
new file mode 100644
index 0000000..e280530
--- /dev/null
+++ b/se5/TypewriterEffect/SubRipParser.cs
@@ -0,0 +1,88 @@
+using System.Globalization;
+using System.Text;
+using System.Text.RegularExpressions;
+
+namespace SubtitleEdit.Plugins.TypewriterEffect;
+
+public sealed class SrtBlock
+{
+    public long StartMs { get; set; }
+    public long EndMs { get; set; }
+    public string Text { get; set; } = string.Empty;
+}
+
+public static class SubRipParser
+{
+    private static readonly Regex TimeLine = new(
+        @"^(\d{1,2}):(\d{2}):(\d{2})[,.](\d{3})\s*-->\s*(\d{1,2}):(\d{2}):(\d{2})[,.](\d{3})",
+        RegexOptions.Compiled);
+
+    public static List<SrtBlock> Parse(string srt)
+    {
+        var result = new List<SrtBlock>();
+        if (string.IsNullOrWhiteSpace(srt))
+        {
+            return result;
+        }
+
+        var normalized = srt.Replace("\r\n", "\n").Trim('\n');
+        var rawBlocks = Regex.Split(normalized, @"\n[ \t]*\n");
+        foreach (var raw in rawBlocks)
+        {
+            var lines = raw.Split('\n');
+            // lines[0] = sequence number, lines[1] = times, lines[2..] = text
+            if (lines.Length < 3)
+            {
+                continue;
+            }
+
+            var timeMatch = TimeLine.Match(lines[1]);
+            if (!timeMatch.Success)
+            {
+                continue;
+            }
+
+            var startMs = ToMs(timeMatch, 1);
+            var endMs = ToMs(timeMatch, 5);
+            var text = string.Join("\n", lines, 2, lines.Length - 2);
+            result.Add(new SrtBlock { StartMs = startMs, EndMs = endMs, Text = text });
+        }
+
+        return result;
+    }
+
+    public static string Serialize(IList<SrtBlock> blocks)
+    {
+        var sb = new StringBuilder();
+        for (var i = 0; i < blocks.Count; i++)
+        {
+            sb.Append(i + 1).Append('\n');
+            sb.Append(FormatTime(blocks[i].StartMs)).Append(" --> ").Append(FormatTime(blocks[i].EndMs)).Append('\n');
+            sb.Append(blocks[i].Text).Append('\n').Append('\n');
+        }
+
+        return sb.ToString().Replace("\n", "\r\n");
+    }
+
+    private static long ToMs(Match m, int firstGroup)
+    {
+        var h = int.Parse(m.Groups[firstGroup].Value, CultureInfo.InvariantCulture);
+        var mn = int.Parse(m.Groups[firstGroup + 1].Value, CultureInfo.InvariantCulture);
+        var s = int.Parse(m.Groups[firstGroup + 2].Value, CultureInfo.InvariantCulture);
+        var ms = int.Parse(m.Groups[firstGroup + 3].Value, CultureInfo.InvariantCulture);
+        return ((h * 60L + mn) * 60 + s) * 1000 + ms;
+    }
+
+    private static string FormatTime(long ms)
+    {
+        if (ms < 0)
+        {
+            ms = 0;
+        }
+        var h = ms / 3_600_000;
+        var mn = (ms / 60_000) % 60;
+        var s = (ms / 1000) % 60;
+        var msr = ms % 1000;
+        return $"{h:D2}:{mn:D2}:{s:D2},{msr:D3}";
+    }
+}
diff --git a/se5/TypewriterEffect/TypewriterEffect.csproj b/se5/TypewriterEffect/TypewriterEffect.csproj
new file mode 100644
index 0000000..ba50523
--- /dev/null
+++ b/se5/TypewriterEffect/TypewriterEffect.csproj
@@ -0,0 +1,22 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <AssemblyName>TypewriterEffect</AssemblyName>
+    <RootNamespace>SubtitleEdit.Plugins.TypewriterEffect</RootNamespace>
+    <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
+    <BuiltInComInteropSupport>true</BuiltInComInteropSupport>
+    <ApplicationManifest>app.manifest</ApplicationManifest>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Avalonia" Version="11.2.2" />
+    <PackageReference Include="Avalonia.Desktop" Version="11.2.2" />
+    <PackageReference Include="Avalonia.Themes.Fluent" Version="11.2.2" />
+    <PackageReference Include="Avalonia.Fonts.Inter" Version="11.2.2" />
+  </ItemGroup>
+
+</Project>
diff --git a/se5/TypewriterEffect/TypewriterEngine.cs b/se5/TypewriterEffect/TypewriterEngine.cs
new file mode 100644
index 0000000..6f656e0
--- /dev/null
+++ b/se5/TypewriterEffect/TypewriterEngine.cs
@@ -0,0 +1,219 @@
+using System.Text;
+
+namespace SubtitleEdit.Plugins.TypewriterEffect;
+
+/// <summary>
+/// Port of the SE4 EffectTypewriter logic: each selected paragraph is replaced
+/// by N short paragraphs that progressively reveal the text character by
+/// character, optionally followed by a final paragraph holding the full line
+/// for <paramref name="endDelaySeconds"/> before the original end time.
+/// </summary>
+public static class TypewriterEngine
+{
+    public static (List<SrtBlock> Blocks, int ChangedCount) Apply(
+        List<SrtBlock> blocks,
+        HashSet<int> selectedIndices,
+        double endDelaySeconds)
+    {
+        var output = new List<SrtBlock>(blocks.Count);
+        var changed = 0;
+        for (var i = 0; i < blocks.Count; i++)
+        {
+            var block = blocks[i];
+            // Empty SelectedIndices means "apply to every line" (matches plugin contract).
+            var isSelected = selectedIndices.Count == 0 || selectedIndices.Contains(i);
+            if (!isSelected)
+            {
+                output.Add(block);
+                continue;
+            }
+
+            var generated = GenerateForParagraph(block, endDelaySeconds);
+            if (generated.Count > 0)
+            {
+                output.AddRange(generated);
+                changed++;
+            }
+            else
+            {
+                output.Add(block);
+            }
+        }
+
+        return (output, changed);
+    }
+
+    private static List<SrtBlock> GenerateForParagraph(SrtBlock p, double endDelaySeconds)
+    {
+        var totalMs = p.EndMs - p.StartMs;
+        if (totalMs <= 500 || string.IsNullOrEmpty(p.Text))
+        {
+            return new List<SrtBlock>();
+        }
+
+        var endDelayMs = (long)(endDelaySeconds * 1000);
+        if (endDelayMs >= totalMs - 200)
+        {
+            endDelayMs = Math.Max(0, totalMs - 200);
+        }
+
+        var workDurationMs = totalMs - endDelayMs;
+        var visibleCharCount = CountVisibleChars(p.Text);
+        if (visibleCharCount == 0)
+        {
+            return new List<SrtBlock>();
+        }
+
+        var stepMs = workDurationMs / (double)visibleCharCount;
+
+        var result = new List<SrtBlock>();
+        var text = string.Empty;
+        var tag = string.Empty;
+        var beforeEndTag = string.Empty;
+        var alignment = string.Empty;
+        var tagOn = false;
+        var index = 0;
+        var i = 0;
+
+        // Eat any leading ASSA override block(s) into "alignment" so it prefixes every emitted paragraph.
+        if (p.Text.StartsWith("{\\", StringComparison.Ordinal))
+        {
+            var j = 0;
+            while (j < p.Text.Length && p.Text[j] == '{' && j + 1 < p.Text.Length && p.Text[j + 1] == '\\')
+            {
+                var close = p.Text.IndexOf('}', j);
+                if (close < 0)
+                {
+                    break;
+                }
+                j = close + 1;
+            }
+            alignment = p.Text.Substring(0, j);
+            i = j;
+        }
+
+        while (i < p.Text.Length)
+        {
+            if (p.Text[i] == '{' && i + 1 < p.Text.Length && p.Text[i + 1] == '\\')
+            {
+                var endIndex = p.Text.IndexOf('}', i);
+                if (endIndex >= 0)
+                {
+                    // Inline ASSA override - keep it attached to the current text but don't tick the clock.
+                    text += p.Text.Substring(i, endIndex - i + 1);
+                    i = endIndex + 1;
+                    continue;
+                }
+            }
+
+            if (tagOn)
+            {
+                tag += p.Text[i];
+                if (p.Text[i] == '>')
+                {
+                    tagOn = false;
+                    var lowered = tag.ToLowerInvariant();
+                    if (lowered.StartsWith("<font ", StringComparison.Ordinal))
+                    {
+                        beforeEndTag = "</font>";
+                    }
+                    else if (lowered == "<i>")
+                    {
+                        beforeEndTag = "</i>";
+                    }
+                    else if (lowered == "<b>")
+                    {
+                        beforeEndTag = "</b>";
+                    }
+                    else if (lowered == "<u>")
+                    {
+                        beforeEndTag = "</u>";
+                    }
+                    else if (lowered.StartsWith("</", StringComparison.Ordinal))
+                    {
+                        beforeEndTag = string.Empty;
+                    }
+                }
+            }
+            else if (p.Text[i] == '<')
+            {
+                tagOn = true;
+                tag = "<";
+            }
+            else
+            {
+                text += tag + p.Text[i];
+                tag = string.Empty;
+
+                var startMs = p.StartMs + (long)(index * stepMs);
+                var endMs = p.StartMs + (long)((index + 1) * stepMs) - 1;
+                if (endMs < startMs)
+                {
+                    endMs = startMs;
+                }
+                result.Add(new SrtBlock
+                {
+                    StartMs = startMs,
+                    EndMs = endMs,
+                    Text = alignment + text + beforeEndTag,
+                });
+                index++;
+            }
+
+            i++;
+        }
+
+        if (endDelayMs > 0 && result.Count > 0)
+        {
+            var startMs = p.StartMs + workDurationMs;
+            result.Add(new SrtBlock { StartMs = startMs, EndMs = p.EndMs, Text = p.Text });
+        }
+        else if (result.Count > 0)
+        {
+            result[^1].EndMs = p.EndMs;
+        }
+
+        return result;
+    }
+
+    private static int CountVisibleChars(string text)
+    {
+        var count = 0;
+        var i = 0;
+        var inTag = false;
+        while (i < text.Length)
+        {
+            if (text[i] == '{' && i + 1 < text.Length && text[i + 1] == '\\')
+            {
+                var end = text.IndexOf('}', i);
+                if (end >= 0)
+                {
+                    i = end + 1;
+                    continue;
+                }
+            }
+
+            if (text[i] == '<')
+            {
+                inTag = true;
+                i++;
+                continue;
+            }
+
+            if (text[i] == '>')
+            {
+                inTag = false;
+                i++;
+                continue;
+            }
+
+            if (!inTag)
+            {
+                count++;
+            }
+
+            i++;
+        }
+        return count;
+    }
+}
diff --git a/se5/TypewriterEffect/app.manifest b/se5/TypewriterEffect/app.manifest
new file mode 100644
index 0000000..6473d20
--- /dev/null
+++ b/se5/TypewriterEffect/app.manifest
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1">
+  <assemblyIdentity version="1.0.0.0" name="SubtitleEdit.Plugins.TypewriterEffect" />
+  <application xmlns="urn:schemas-microsoft-com:asm.v3">
+    <windowsSettings>
+      <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">true/pm</dpiAware>
+      <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2</dpiAwareness>
+    </windowsSettings>
+  </application>
+</assembly>
diff --git a/se5/TypewriterEffect/plugin.json b/se5/TypewriterEffect/plugin.json
new file mode 100644
index 0000000..8e630f6
--- /dev/null
+++ b/se5/TypewriterEffect/plugin.json
@@ -0,0 +1,12 @@
+{
+  "apiVersion": 1,
+  "name": "Typewriter effect",
+  "description": "Splits each subtitle line into short timed parts that progressively reveal the text, character by character.",
+  "version": "1.0.0",
+  "author": "Subtitle Edit",
+  "url": "https://github.com/SubtitleEdit/plugins/tree/main/se5/TypewriterEffect",
+  "menu": "Tools",
+  "minSeVersion": "5.0.0",
+  "runtime": "dotnet",
+  "entry": "TypewriterEffect.dll"
+}