diff --git a/src/Chip8.Replay/QuirksCodec.cs b/src/Chip8.Replay/QuirksCodec.cs
new file mode 100644
index 0000000..51cfa79
--- /dev/null
+++ b/src/Chip8.Replay/QuirksCodec.cs
@@ -0,0 +1,103 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Chip8.Core;
+
+namespace Chip8.Replay;
+
+public static class QuirksCodec
+{
+    const int shiftUsesVyBit = 0;
+    const int jumpWithVxBit = 1;
+    const int loadStoreIncrementsIBit = 2;
+    const int resetVfOnLogicBit = 3;
+    const int clipSpritesBit = 4;
+    const int addToIndexSetsCarryBit = 5;
+
+    static readonly (string token, int bit)[] tokens =
+    {
+        ("shiftVy", shiftUsesVyBit),
+        ("jumpVx", jumpWithVxBit),
+        ("incI", loadStoreIncrementsIBit),
+        ("resetVf", resetVfOnLogicBit),
+        ("clip", clipSpritesBit),
+        ("carryI", addToIndexSetsCarryBit),
+    };
+
+    public static byte toByte(Quirks quirks)
+    {
+        int packed = 0;
+        if (quirks.shiftUsesVy) packed |= 1 << shiftUsesVyBit;
+        if (quirks.jumpWithVx) packed |= 1 << jumpWithVxBit;
+        if (quirks.loadStoreIncrementsI) packed |= 1 << loadStoreIncrementsIBit;
+        if (quirks.resetVfOnLogic) packed |= 1 << resetVfOnLogicBit;
+        if (quirks.clipSprites) packed |= 1 << clipSpritesBit;
+        if (quirks.addToIndexSetsCarry) packed |= 1 << addToIndexSetsCarryBit;
+        return (byte)packed;
+    }
+
+    public static Quirks fromByte(byte packed) => new Quirks
+    {
+        shiftUsesVy = (packed & (1 << shiftUsesVyBit)) != 0,
+        jumpWithVx = (packed & (1 << jumpWithVxBit)) != 0,
+        loadStoreIncrementsI = (packed & (1 << loadStoreIncrementsIBit)) != 0,
+        resetVfOnLogic = (packed & (1 << resetVfOnLogicBit)) != 0,
+        clipSprites = (packed & (1 << clipSpritesBit)) != 0,
+        addToIndexSetsCarry = (packed & (1 << addToIndexSetsCarryBit)) != 0,
+    };
+
+    public static string toTokens(Quirks quirks)
+    {
+        byte packed = toByte(quirks);
+        var active = new List<string>();
+        foreach (var (token, bit) in tokens)
+        {
+            if ((packed & (1 << bit)) != 0)
+            {
+                active.Add(token);
+            }
+        }
+        return active.Count == 0 ? "none" : string.Join("+", active);
+    }
+
+    public static Quirks fromTokens(string text)
+    {
+        byte packed = 0;
+        string trimmed = text.Trim();
+        if (trimmed == "none" || trimmed.Length == 0)
+        {
+            return fromByte(0);
+        }
+
+        foreach (string chunk in trimmed.Split('+'))
+        {
+            string token = chunk.Trim();
+            if (token.Length == 0)
+            {
+                continue;
+            }
+
+            bool matched = false;
+            foreach (var (candidate, bit) in tokens)
+            {
+                if (string.Equals(candidate, token, StringComparison.OrdinalIgnoreCase))
+                {
+                    packed |= (byte)(1 << bit);
+                    matched = true;
+                    break;
+                }
+            }
+
+            if (!matched)
+            {
+                throw new FormatException("unknown quirk token '" + token + "'");
+            }
+        }
+
+        return fromByte(packed);
+    }
+
+    public static Quirks clone(Quirks quirks) => fromByte(toByte(quirks));
+
+    public static bool sameFlags(Quirks left, Quirks right) => toByte(left) == toByte(right);
+}
diff --git a/src/Chip8.Replay/RomLibrary.cs b/src/Chip8.Replay/RomLibrary.cs
new file mode 100644
index 0000000..fcca86b
--- /dev/null
+++ b/src/Chip8.Replay/RomLibrary.cs
@@ -0,0 +1,72 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace Chip8.Replay;
+
+public sealed class RomLibrary
+{
+    readonly string romDirectory;
+    readonly Dictionary<string, byte[]> cache = new Dictionary<string, byte[]>(StringComparer.Ordinal);
+
+    public RomLibrary(string romDirectory)
+    {
+        this.romDirectory = romDirectory;
+    }
+
+    public string directory => romDirectory;
+
+    public static RomLibrary locate()
+    {
+        var dir = new DirectoryInfo(AppContext.BaseDirectory);
+        while (dir is not null && !Directory.Exists(Path.Combine(dir.FullName, "roms")))
+        {
+            dir = dir.Parent;
+        }
+
+        if (dir is null)
+        {
+            throw new DirectoryNotFoundException("could not locate a 'roms' directory above " + AppContext.BaseDirectory);
+        }
+
+        return new RomLibrary(Path.Combine(dir.FullName, "roms"));
+    }
+
+    public bool has(string name) => File.Exists(pathOf(name));
+
+    public string pathOf(string name) => Path.Combine(romDirectory, name);
+
+    public byte[] load(string name)
+    {
+        if (cache.TryGetValue(name, out byte[]? cached))
+        {
+            return cached;
+        }
+
+        string path = pathOf(name);
+        if (!File.Exists(path))
+        {
+            throw new FileNotFoundException("rom '" + name + "' not found under " + romDirectory, path);
+        }
+
+        byte[] bytes = File.ReadAllBytes(path);
+        cache[name] = bytes;
+        return bytes;
+    }
+
+    public IReadOnlyList<string> available()
+    {
+        var names = new List<string>();
+        if (!Directory.Exists(romDirectory))
+        {
+            return names;
+        }
+
+        foreach (string path in Directory.GetFiles(romDirectory, "*.ch8"))
+        {
+            names.Add(Path.GetFileName(path));
+        }
+        names.Sort(StringComparer.Ordinal);
+        return names;
+    }
+}