diff --git a/src/TeamsISO.App/Services/OutputNameTemplate.cs b/src/TeamsISO.App/Services/OutputNameTemplate.cs
new file mode 100644
index 0000000..491ea6d
--- /dev/null
+++ b/src/TeamsISO.App/Services/OutputNameTemplate.cs
@@ -0,0 +1,107 @@
+using System.IO;
+using System.Text;
+
+namespace TeamsISO.App.Services;
+
+/// <summary>
+/// User-editable template for the NDI source name a participant's ISO is
+/// published as. Default <c>"TEAMSISO_{guid}"</c> matches the original
+/// hard-coded <c>DefaultOutputName</c> in <c>IsoController</c>; operators
+/// can switch to <c>"TEAMSISO_{name}"</c> for human-readable output names
+/// (recommended for downstream switchers that key on name patterns), or
+/// <c>"TEAMSISO_{machine}_{name}"</c> when multiple TeamsISO machines feed
+/// the same NDI network.
+///
+/// Tokens expanded in <see cref="Render"/>:
+///   <c>{name}</c>      participant display name, sanitized (alphanumeric + underscore)
+///   <c>{guid}</c>      first 8 hex chars of the participant's Id, uppercase
+///   <c>{machine}</c>   sanitized PC hostname (Environment.MachineName)
+///   <c>{timestamp}</c> current local time as <c>yyyyMMdd_HHmmss</c>
+///
+/// Persisted to <c>%LOCALAPPDATA%\TeamsISO\output-name-template.txt</c>.
+/// </summary>
+public static class OutputNameTemplate
+{
+    public const string DefaultTemplate = "TEAMSISO_{guid}";
+
+    private static string TemplatePath =>
+        Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+            "TeamsISO", "output-name-template.txt");
+
+    /// <summary>
+    /// Get the operator's current template, or the shipped default when no
+    /// override has been saved (or the override file is missing/unreadable).
+    /// </summary>
+    public static string Get()
+    {
+        try
+        {
+            if (File.Exists(TemplatePath))
+            {
+                var raw = File.ReadAllText(TemplatePath).Trim();
+                if (!string.IsNullOrEmpty(raw)) return raw;
+            }
+        }
+        catch
+        {
+            // Disk read failure → fall through to default. The next Set() call
+            // will overwrite cleanly.
+        }
+        return DefaultTemplate;
+    }
+
+    public static void Set(string template)
+    {
+        try
+        {
+            var dir = Path.GetDirectoryName(TemplatePath);
+            if (!string.IsNullOrEmpty(dir)) Directory.CreateDirectory(dir);
+            File.WriteAllText(TemplatePath, template ?? string.Empty);
+        }
+        catch
+        {
+            // Best-effort persistence; the in-memory value still sticks for
+            // this session.
+        }
+    }
+
+    /// <summary>
+    /// Expand tokens in <paramref name="template"/> for a specific participant.
+    /// Result is sanitized into NDI-safe characters: alphanumeric, underscore,
+    /// hyphen, period. NDI spec allows more, but a conservative set keeps
+    /// downstream switchers happy.
+    /// </summary>
+    public static string Render(string template, Guid participantId, string displayName)
+    {
+        var safeName = SanitizeForNdi(displayName);
+        var guid = participantId.ToString("N")[..8].ToUpperInvariant();
+        var machine = SanitizeForNdi(Environment.MachineName);
+        var timestamp = DateTimeOffset.Now.ToString("yyyyMMdd_HHmmss");
+
+        var result = template
+            .Replace("{name}", safeName)
+            .Replace("{guid}", guid)
+            .Replace("{machine}", machine)
+            .Replace("{timestamp}", timestamp);
+
+        // Final sanitize on the rendered result — protects against a template
+        // that includes literal characters NDI doesn't accept.
+        return SanitizeForNdi(result);
+    }
+
+    private static string SanitizeForNdi(string s)
+    {
+        if (string.IsNullOrEmpty(s)) return string.Empty;
+        var sb = new StringBuilder(s.Length);
+        foreach (var c in s)
+        {
+            if (char.IsLetterOrDigit(c) || c is '_' or '-' or '.')
+                sb.Append(c);
+            else if (char.IsWhiteSpace(c))
+                sb.Append('_');
+            // else: skip
+        }
+        return sb.ToString();
+    }
+}