Add mono switch, live waveform, and WAV cue markers (1.3.0-alpha)

- WavRecorder: optional mono, waveform envelope, cue/adtl marker chunks
- WaveformView: scrolling waveform with red clipped columns
- Marker + MarkerStore; Mark button with label dialog
- PlayerActivity: marker chips that seek; shared seekTo
- InsetsHelper: keep UI clear of status bar/notch and nav bar
- Bump to 1.3.0-alpha (versionCode 4)

15 files changed, 648 insertions, 54 deletions

diff --git a/app/src/main/java/com/wuhei/reccoon/InsetsHelper.java b/app/src/main/java/com/wuhei/reccoon/InsetsHelper.java
new file mode 100644
index 0000000..660fa64
--- /dev/null
+++ b/app/src/main/java/com/wuhei/reccoon/InsetsHelper.java
@@ -0,0 +1,33 @@
+package com.wuhei.reccoon;
+
+import android.view.View;
+
+import androidx.core.graphics.Insets;
+import androidx.core.view.ViewCompat;
+import androidx.core.view.WindowInsetsCompat;
+
+/**
+ * Adds the system bar insets to a root view's padding so content is not hidden
+ * behind the status bar / notch or the navigation bar (edge-to-edge safe).
+ */
+public final class InsetsHelper {
+
+    private InsetsHelper() {
+    }
+
+    public static void apply(View root) {
+        if (root == null) {
+            return;
+        }
+        final int left = root.getPaddingLeft();
+        final int top = root.getPaddingTop();
+        final int right = root.getPaddingRight();
+        final int bottom = root.getPaddingBottom();
+        ViewCompat.setOnApplyWindowInsetsListener(root, (view, windowInsets) -> {
+            Insets insets = windowInsets.getInsets(WindowInsetsCompat.Type.systemBars());
+            view.setPadding(left + insets.left, top + insets.top,
+                    right + insets.right, bottom + insets.bottom);
+            return windowInsets;
+        });
+    }
+}
diff --git a/app/src/main/java/com/wuhei/reccoon/MainActivity.java b/app/src/main/java/com/wuhei/reccoon/MainActivity.java
index c687fcb..c8daf44 100644
--- a/app/src/main/java/com/wuhei/reccoon/MainActivity.java
+++ b/app/src/main/java/com/wuhei/reccoon/MainActivity.java
@@ -10,6 +10,7 @@ import android.content.Intent;
 import android.content.SharedPreferences;
 import android.content.pm.PackageManager;
 import android.provider.Settings;
+import android.text.InputType;
 import android.media.MediaScannerConnection;
 import android.net.Uri;
 import android.os.Build;
@@ -21,6 +22,9 @@ import android.os.SystemClock;
 import android.provider.MediaStore;
 import android.view.View;
 import android.view.WindowManager;
+import android.widget.Button;
+import android.widget.EditText;
+import android.widget.FrameLayout;
 import android.widget.ImageButton;
 import android.widget.ImageView;
 import android.widget.TextView;
@@ -31,6 +35,9 @@ import androidx.appcompat.app.AlertDialog;
 import androidx.appcompat.app.AppCompatActivity;
 import androidx.appcompat.widget.AppCompatCheckBox;
 import androidx.core.content.ContextCompat;
+import androidx.core.graphics.Insets;
+import androidx.core.view.ViewCompat;
+import androidx.core.view.WindowInsetsCompat;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -40,6 +47,7 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.text.SimpleDateFormat;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Date;
 import java.util.List;
 import java.util.Locale;
@@ -50,13 +58,17 @@ public class MainActivity extends AppCompatActivity {
     private static final String PREFS = "reccoon";
     private static final String PREF_COUNTER = "counter";
     private static final String PREF_SILENCE = "silence_notifications";
+    private static final String PREF_MONO = "mono_recording";
 
     private ImageButton recordButton;
     private ImageView recIndicator;
     private TextView timerText;
     private TextView statusText;
     private LevelMeterView levelMeter;
+    private WaveformView waveformView;
     private AppCompatCheckBox silenceCheckbox;
+    private AppCompatCheckBox monoCheckbox;
+    private Button markButton;
     private int savedInterruptionFilter = -1;
 
     private WavRecorder recorder;
@@ -78,17 +90,24 @@ public class MainActivity extends AppCompatActivity {
         timerText = findViewById(R.id.timerText);
         statusText = findViewById(R.id.statusText);
         levelMeter = findViewById(R.id.levelMeter);
+        waveformView = findViewById(R.id.waveformView);
         silenceCheckbox = findViewById(R.id.silenceCheckbox);
+        monoCheckbox = findViewById(R.id.monoCheckbox);
+        markButton = findViewById(R.id.markButton);
 
         recorder = new WavRecorder(this);
-        recorder.setLevelListener((leftPeak, rightPeak, clipped) ->
+        recorder.setLevelListener((leftPeak, rightPeak, clipped, waveform) ->
                 runOnUiThread(() -> {
                     if (recording) {
                         levelMeter.setLevels(leftPeak, rightPeak, clipped);
+                        waveformView.append(waveform);
                     }
                 }));
 
         setUpSilence();
+        setUpMono();
+        markButton.setOnClickListener(v -> addMarker());
+        applyWindowInsets();
 
         blinkAnimator = ObjectAnimator.ofFloat(recIndicator, View.ALPHA, 1f, 0.15f);
         blinkAnimator.setDuration(600);
@@ -168,6 +187,57 @@ public class MainActivity extends AppCompatActivity {
         });
     }
 
+    private void setUpMono() {
+        SharedPreferences prefs = getSharedPreferences(PREFS, MODE_PRIVATE);
+        boolean mono = prefs.getBoolean(PREF_MONO, false);
+        monoCheckbox.setChecked(mono);
+        recorder.setForceMono(mono);
+        monoCheckbox.setOnCheckedChangeListener((button, checked) -> {
+            getSharedPreferences(PREFS, MODE_PRIVATE)
+                    .edit().putBoolean(PREF_MONO, checked).apply();
+            recorder.setForceMono(checked);
+        });
+    }
+
+    private void addMarker() {
+        if (!recording) {
+            return;
+        }
+        final long offset = recorder.currentSampleOffset();
+        final int next = recorder.getMarkers().size() + 1;
+
+        EditText input = new EditText(this);
+        input.setInputType(InputType.TYPE_CLASS_TEXT);
+        input.setHint(R.string.marker_hint);
+        input.setText(getString(R.string.marker_fmt, next));
+        input.selectAll();
+
+        int padding = (int) (20 * getResources().getDisplayMetrics().density);
+        FrameLayout container = new FrameLayout(this);
+        container.setPadding(padding, padding / 2, padding, 0);
+        container.addView(input);
+
+        new AlertDialog.Builder(this)
+                .setTitle(R.string.marker_title)
+                .setView(container)
+                .setPositiveButton(R.string.marker_add, (dialog, which) -> {
+                    String label = input.getText().toString().trim();
+                    if (label.isEmpty()) {
+                        label = getString(R.string.marker_fmt, next);
+                    }
+                    recorder.addMarkerAt(offset, label);
+                    Toast.makeText(this, getString(R.string.marker_added_fmt, next),
+                            Toast.LENGTH_SHORT).show();
+                })
+                .setNegativeButton(R.string.cancel, null)
+                .show();
+    }
+
+    /** Keeps the UI clear of the status bar/notch and the navigation bar. */
+    private void applyWindowInsets() {
+        InsetsHelper.apply(findViewById(R.id.root));
+    }
+
     private void ensureDndAccess() {
         if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
             return;
@@ -221,6 +291,7 @@ public class MainActivity extends AppCompatActivity {
     }
 
     private void startRecording() {
+        recorder.setForceMono(monoCheckbox.isChecked());
         try {
             recorder.start();
         } catch (Exception e) {
@@ -232,6 +303,8 @@ public class MainActivity extends AppCompatActivity {
         startedAtMs = SystemClock.elapsedRealtime();
 
         levelMeter.reset();
+        waveformView.reset();
+        markButton.setEnabled(true);
         applySilence(true);
         recordButton.setBackgroundResource(R.drawable.bg_record_active);
         recordButton.setContentDescription(getString(R.string.cd_stop));
@@ -257,6 +330,8 @@ public class MainActivity extends AppCompatActivity {
         busy = true;
 
         levelMeter.reset();
+        waveformView.reset();
+        markButton.setEnabled(false);
         applySilence(false);
         long elapsed = SystemClock.elapsedRealtime() - startedAtMs;
         handler.removeCallbacks(timerRunnable);
@@ -271,16 +346,22 @@ public class MainActivity extends AppCompatActivity {
 
         new Thread(() -> {
             File wav;
+            List<Marker> markers;
             try {
                 wav = recorder.stop();
+                markers = recorder.getMarkers();
             } catch (Exception e) {
                 wav = null;
+                markers = Collections.emptyList();
             }
 
             String savedName = null;
             if (wav != null) {
                 try {
                     savedName = saveToDownloads(wav);
+                    if (savedName != null && !markers.isEmpty()) {
+                        new MarkerStore(this).save(savedName, markers);
+                    }
                 } catch (Exception ignored) {
                     savedName = null;
                 }
diff --git a/app/src/main/java/com/wuhei/reccoon/Marker.java b/app/src/main/java/com/wuhei/reccoon/Marker.java
new file mode 100644
index 0000000..d4a7ef5
--- /dev/null
+++ b/app/src/main/java/com/wuhei/reccoon/Marker.java
@@ -0,0 +1,19 @@
+package com.wuhei.reccoon;
+
+/** A user-placed marker inside a recording, stored as a WAV cue point. */
+public final class Marker {
+
+    public final int index;
+    public final long sampleOffset;
+    public final String label;
+
+    public Marker(int index, long sampleOffset, String label) {
+        this.index = index;
+        this.sampleOffset = sampleOffset;
+        this.label = label == null ? "" : label;
+    }
+
+    public long timeMillis() {
+        return sampleOffset * 1000L / WavRecorder.SAMPLE_RATE;
+    }
+}
diff --git a/app/src/main/java/com/wuhei/reccoon/MarkerStore.java b/app/src/main/java/com/wuhei/reccoon/MarkerStore.java
new file mode 100644
index 0000000..9002264
--- /dev/null
+++ b/app/src/main/java/com/wuhei/reccoon/MarkerStore.java
@@ -0,0 +1,97 @@
+package com.wuhei.reccoon;
+
+import android.content.Context;
+
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Stores recording markers as JSON sidecars (the same markers are also
+ * embedded in the WAV itself as {@code cue } / {@code adtl} chunks).
+ */
+public final class MarkerStore {
+
+    private final File dir;
+
+    public MarkerStore(Context context) {
+        dir = new File(context.getApplicationContext().getFilesDir(), "markers");
+    }
+
+    public boolean has(String recordingName) {
+        return fileFor(recordingName).isFile();
+    }
+
+    public void save(String recordingName, List<Marker> markers) throws IOException {
+        if (markers.isEmpty()) {
+            return;
+        }
+        JSONArray array = new JSONArray();
+        try {
+            for (Marker marker : markers) {
+                JSONObject item = new JSONObject();
+                item.put("index", marker.index);
+                item.put("offset", marker.sampleOffset);
+                item.put("label", marker.label);
+                array.put(item);
+            }
+        } catch (JSONException e) {
+            throw new IOException(e);
+        }
+
+        if (!dir.exists() && !dir.mkdirs()) {
+            throw new IOException("Cannot create marker directory");
+        }
+        String json;
+        try {
+            json = array.toString(2);
+        } catch (JSONException e) {
+            throw new IOException(e);
+        }
+        try (FileOutputStream out = new FileOutputStream(fileFor(recordingName))) {
+            out.write(json.getBytes(StandardCharsets.UTF_8));
+        }
+    }
+
+    public List<Marker> load(String recordingName) {
+        List<Marker> markers = new ArrayList<>();
+        File file = fileFor(recordingName);
+        if (!file.isFile()) {
+            return markers;
+        }
+        try (InputStream in = new java.io.FileInputStream(file)) {
+            byte[] buffer = new byte[(int) file.length()];
+            int read = 0;
+            while (read < buffer.length) {
+                int n = in.read(buffer, read, buffer.length - read);
+                if (n < 0) {
+                    break;
+                }
+                read += n;
+            }
+            JSONArray array = new JSONArray(new String(buffer, 0, read, StandardCharsets.UTF_8));
+            for (int i = 0; i < array.length(); i++) {
+                JSONObject item = array.getJSONObject(i);
+                markers.add(new Marker(
+                        item.optInt("index", i + 1),
+                        item.optLong("offset", 0),
+                        item.optString("label", "")));
+            }
+        } catch (Exception e) {
+            // Return whatever we parsed.
+        }
+        return markers;
+    }
+
+    private File fileFor(String recordingName) {
+        return new File(dir, recordingName + ".json");
+    }
+}
diff --git a/app/src/main/java/com/wuhei/reccoon/PlayerActivity.java b/app/src/main/java/com/wuhei/reccoon/PlayerActivity.java
index e882fbc..6ebff5b 100644
--- a/app/src/main/java/com/wuhei/reccoon/PlayerActivity.java
+++ b/app/src/main/java/com/wuhei/reccoon/PlayerActivity.java
@@ -20,6 +20,7 @@ import android.widget.Toast;
 import androidx.appcompat.app.AlertDialog;
 import androidx.appcompat.app.AppCompatActivity;
 
+import java.util.List;
 import java.util.Locale;
 
 /**
@@ -50,6 +51,8 @@ public class PlayerActivity extends AppCompatActivity {
     private Spinner modelSpinner;
     private ProgressBar progressBar;
     private LinearLayout transcriptContainer;
+    private LinearLayout markersSection;
+    private LinearLayout markersContainer;
 
     private final Handler handler = new Handler(Looper.getMainLooper());
     private boolean userSeeking;
@@ -59,6 +62,7 @@ public class PlayerActivity extends AppCompatActivity {
 
     private ModelRepository models;
     private TranscriptStore transcripts;
+    private MarkerStore markerStore;
 
     private final Runnable ticker = new Runnable() {
         @Override
@@ -84,6 +88,7 @@ public class PlayerActivity extends AppCompatActivity {
 
         models = new ModelRepository(this);
         transcripts = new TranscriptStore(this);
+        markerStore = new MarkerStore(this);
 
         titleText = findViewById(R.id.titleText);
         timeText = findViewById(R.id.timeText);
@@ -96,6 +101,8 @@ public class PlayerActivity extends AppCompatActivity {
         modelSpinner = findViewById(R.id.modelSpinner);
         progressBar = findViewById(R.id.progressBar);
         transcriptContainer = findViewById(R.id.transcriptContainer);
+        markersSection = findViewById(R.id.markersSection);
+        markersContainer = findViewById(R.id.markersContainer);
 
         titleText.setText(RecordingsActivity.prettyName(recordingName));
 
@@ -103,6 +110,9 @@ public class PlayerActivity extends AppCompatActivity {
         setUpButtons();
         setUpPlayer();
 
+        InsetsHelper.apply(findViewById(R.id.root));
+        showMarkers(markerStore.load(recordingName));
+
         TranscriptionEngine.Result existing = transcripts.load(recordingName);
         if (existing != null) {
             showTranscript(existing);
@@ -407,18 +417,52 @@ public class PlayerActivity extends AppCompatActivity {
         view.setTextSize(15f);
         view.setPadding(0, 12, 0, 12);
         view.setBackgroundResource(android.R.drawable.list_selector_background);
-        view.setOnClickListener(v -> {
-            if (player != null && prepared) {
-                player.seekTo(Math.max(0, Math.min(seekMs, player.getDuration())));
-                if (!player.isPlaying()) {
-                    player.start();
-                    applySpeed();
-                }
-            }
-        });
+        view.setOnClickListener(v -> seekTo(seekMs));
         transcriptContainer.addView(view);
     }
 
+    private void showMarkers(List<Marker> markers) {
+        markersContainer.removeAllViews();
+        markersSection.setVisibility(markers.isEmpty() ? View.GONE : View.VISIBLE);
+        float density = getResources().getDisplayMetrics().density;
+        for (Marker marker : markers) {
+            TextView chip = new TextView(this);
+            StringBuilder text = new StringBuilder();
+            text.append('M').append(marker.index)
+                    .append("  ").append(formatClock((int) marker.timeMillis()));
+            if (!marker.label.isEmpty()) {
+                text.append("  ").append(marker.label);
+            }
+            chip.setText(text.toString());
+            chip.setTextColor(getResources().getColor(R.color.text_primary, getTheme()));
+            chip.setTextSize(13f);
+            chip.setPadding((int) (12 * density), (int) (6 * density),
+                    (int) (12 * density), (int) (6 * density));
+            chip.setBackgroundResource(R.drawable.badge_marker);
+            chip.setOnClickListener(v -> seekTo((int) marker.timeMillis()));
+            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
+                    LinearLayout.LayoutParams.WRAP_CONTENT,
+                    LinearLayout.LayoutParams.WRAP_CONTENT);
+            params.rightMargin = (int) (8 * density);
+            chip.setLayoutParams(params);
+            markersContainer.addView(chip);
+        }
+    }
+
+    private void seekTo(int millis) {
+        if (player == null || !prepared) {
+            return;
+        }
+        int target = Math.max(0, Math.min(millis, player.getDuration()));
+        player.seekTo(target);
+        seekBar.setProgress(target);
+        if (!player.isPlaying()) {
+            player.start();
+            applySpeed();
+        }
+        updateTimeLabel();
+    }
+
     private static String languageFor(int position) {
         switch (position) {
             case 1:
diff --git a/app/src/main/java/com/wuhei/reccoon/RecordingsActivity.java b/app/src/main/java/com/wuhei/reccoon/RecordingsActivity.java
index 9551ef5..7424e10 100644
--- a/app/src/main/java/com/wuhei/reccoon/RecordingsActivity.java
+++ b/app/src/main/java/com/wuhei/reccoon/RecordingsActivity.java
@@ -34,6 +34,8 @@ public class RecordingsActivity extends AppCompatActivity {
         transcripts = new TranscriptStore(this);
         emptyText = findViewById(R.id.emptyText);
 
+        InsetsHelper.apply(findViewById(R.id.root));
+
         ListView listView = findViewById(R.id.recordingsList);
         adapter = new Adapter();
         listView.setAdapter(adapter);
diff --git a/app/src/main/java/com/wuhei/reccoon/WavRecorder.java b/app/src/main/java/com/wuhei/reccoon/WavRecorder.java
index 3e82837..8279847 100644
--- a/app/src/main/java/com/wuhei/reccoon/WavRecorder.java
+++ b/app/src/main/java/com/wuhei/reccoon/WavRecorder.java
@@ -6,6 +6,7 @@ import android.media.AudioRecord;
 import android.media.MediaRecorder;
 import android.os.SystemClock;
 
+import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.FileOutputStream;
 import java.io.IOException;
@@ -13,14 +14,21 @@ import java.io.RandomAccessFile;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 /**
  * Records uncompressed 16-bit PCM audio at 44.1 kHz and writes a standard
  * RIFF/WAVE file (PCM, format code 1).
  *
  * <p>Stereo is used when the device supports it (so the left/right level
- * meters are meaningful); it falls back to mono otherwise. Peak levels for both
- * channels are reported through {@link LevelListener}.
+ * meters are meaningful); it falls back to mono otherwise. Peak levels and a
+ * small waveform envelope for both channels are reported through
+ * {@link LevelListener}.
+ *
+ * <p>Markers added while recording are embedded in the file as standard WAV
+ * {@code cue } + {@code LIST/adtl} chunks (readable by Audacity, Reaper, ...).
  */
 public class WavRecorder {
 
@@ -29,17 +37,21 @@ public class WavRecorder {
 
     private static final int HEADER_SIZE = 44;
     private static final long LEVEL_INTERVAL_MS = 40;
+    private static final int WAVEFORM_BUCKETS = 16;
 
     public interface LevelListener {
         /**
          * @param leftPeak  0..1 peak of the left channel in this window
          * @param rightPeak 0..1 peak of the right channel (same as left when mono)
          * @param clipped   true if any sample reached full scale in this window
+         * @param waveform  min/max pairs (length {@code 2 * WAVEFORM_BUCKETS}) of
+         *                  the left/mono channel for a scrolling waveform
          */
-        void onLevels(float leftPeak, float rightPeak, boolean clipped);
+        void onLevels(float leftPeak, float rightPeak, boolean clipped, float[] waveform);
     }
 
     private final Context context;
+    private final List<Marker> markers = new ArrayList<>();
 
     private LevelListener levelListener;
     private AudioRecord audioRecord;
@@ -48,6 +60,7 @@ public class WavRecorder {
     private File tempFile;
     private volatile long pcmBytes;
     private int channels = 2;
+    private boolean forceMono;
 
     public WavRecorder(Context context) {
         this.context = context.getApplicationContext();
@@ -57,6 +70,11 @@ public class WavRecorder {
         this.levelListener = listener;
     }
 
+    /** When true, always record a single channel (half the file size). */
+    public void setForceMono(boolean forceMono) {
+        this.forceMono = forceMono;
+    }
+
     /** Effective number of channels used by the last/current recording. */
     public int getChannels() {
         return channels;
@@ -69,6 +87,7 @@ public class WavRecorder {
         if (recording) {
             throw new IllegalStateException("A recording is already in progress");
         }
+        markers.clear();
 
         audioRecord = createAudioRecord();
         if (audioRecord == null) {
@@ -149,10 +168,54 @@ public class WavRecorder {
         if (channelCount == 1) {
             rightPeak = leftPeak;
         }
+
+        float[] waveform = buildWaveform(buffer, frames, frameBytes);
         LevelListener listener = levelListener;
         if (listener != null) {
-            listener.onLevels(leftPeak, rightPeak, clipped);
+            listener.onLevels(leftPeak, rightPeak, clipped, waveform);
+        }
+    }
+
+    private static float[] buildWaveform(byte[] buffer, int frames, int frameBytes) {
+        float[] waveform = new float[WAVEFORM_BUCKETS * 2];
+        int framesPerBucket = Math.max(1, frames / WAVEFORM_BUCKETS);
+        for (int bucket = 0; bucket < WAVEFORM_BUCKETS; bucket++) {
+            int start = bucket * framesPerBucket;
+            int end = bucket == WAVEFORM_BUCKETS - 1 ? frames : start + framesPerBucket;
+            float min = 0f;
+            float max = 0f;
+            for (int i = start; i < end && i < frames; i++) {
+                float sample = pcm16(buffer, i * frameBytes) / 32768f;
+                if (sample < min) {
+                    min = sample;
+                }
+                if (sample > max) {
+                    max = sample;
+                }
+            }
+            waveform[bucket * 2] = min;
+            waveform[bucket * 2 + 1] = max;
         }
+        return waveform;
+    }
+
+    /** Current position in sample frames (usable while recording). */
+    public long currentSampleOffset() {
+        int blockAlign = Math.max(1, channels * 2);
+        return pcmBytes / blockAlign;
+    }
+
+    /** Adds a marker at the current position. */
+    public void addMarker(String label) {
+        addMarkerAt(currentSampleOffset(), label);
+    }
+
+    public void addMarkerAt(long sampleOffset, String label) {
+        markers.add(new Marker(markers.size() + 1, sampleOffset, label));
+    }
+
+    public List<Marker> getMarkers() {
+        return Collections.unmodifiableList(new ArrayList<>(markers));
     }
 
     /**
@@ -192,6 +255,7 @@ public class WavRecorder {
         writerThread = null;
 
         writeHeader();
+        writeMarkers();
         return tempFile;
     }
 
@@ -200,7 +264,9 @@ public class WavRecorder {
     }
 
     private AudioRecord createAudioRecord() {
-        int[] candidates = {AudioFormat.CHANNEL_IN_STEREO, AudioFormat.CHANNEL_IN_MONO};
+        int[] candidates = forceMono
+                ? new int[]{AudioFormat.CHANNEL_IN_MONO}
+                : new int[]{AudioFormat.CHANNEL_IN_STEREO, AudioFormat.CHANNEL_IN_MONO};
         for (int channelConfig : candidates) {
             int minBuffer = AudioRecord.getMinBufferSize(
                     SAMPLE_RATE, channelConfig, AudioFormat.ENCODING_PCM_16BIT);
@@ -248,6 +314,68 @@ public class WavRecorder {
         }
     }
 
+    /** Appends {@code cue } and {@code LIST/adtl} chunks for the markers. */
+    private void writeMarkers() {
+        if (markers.isEmpty() || tempFile == null || !tempFile.isFile()) {
+            return;
+        }
+        try (RandomAccessFile raf = new RandomAccessFile(tempFile, "rw")) {
+            raf.seek(raf.length());
+            raf.write(buildCueChunk(markers));
+            raf.write(buildAdtlChunk(markers));
+
+            long newLength = raf.length();
+            raf.seek(4);
+            raf.write(intLE((int) (newLength - 8)));
+        } catch (IOException ignored) {
+            // Markers are a bonus; the audio itself stays valid.
+        }
+    }
+
+    private static byte[] buildCueChunk(List<Marker> markers) {
+        int count = markers.size();
+        ByteBuffer buffer = ByteBuffer.allocate(8 + 4 + 24 * count).order(ByteOrder.LITTLE_ENDIAN);
+        buffer.put(ascii("cue "));
+        buffer.putInt(4 + 24 * count);
+        buffer.putInt(count);
+        for (Marker marker : markers) {
+            buffer.putInt(marker.index);                 // dwName
+            buffer.putInt(0);                            // dwPosition
+            buffer.put(ascii("data"));                   // fccChunk
+            buffer.putInt(0);                            // dwChunkStart
+            buffer.putInt(0);                            // dwBlockStart
+            buffer.putInt((int) marker.sampleOffset);    // dwSampleOffset
+        }
+        return buffer.array();
+    }
+
+    private static byte[] buildAdtlChunk(List<Marker> markers) {
+        ByteArrayOutputStream out = new ByteArrayOutputStream();
+        for (Marker marker : markers) {
+            byte[] text = marker.label.getBytes(StandardCharsets.UTF_8);
+            int size = 4 + text.length + 1;              // cue id + text + NUL
+            int padded = size + (size & 1);
+            ByteBuffer buffer = ByteBuffer.allocate(8 + padded).order(ByteOrder.LITTLE_ENDIAN);
+            buffer.put(ascii("labl"));
+            buffer.putInt(size);
+            buffer.putInt(marker.index);
+            buffer.put(text);
+            buffer.put((byte) 0);
+            while (buffer.position() < buffer.capacity()) {
+                buffer.put((byte) 0);
+            }
+            out.write(buffer.array(), 0, buffer.array().length);
+        }
+        byte[] adtl = out.toByteArray();
+
+        ByteBuffer list = ByteBuffer.allocate(12 + adtl.length).order(ByteOrder.LITTLE_ENDIAN);
+        list.put(ascii("LIST"));
+        list.putInt(4 + adtl.length);
+        list.put(ascii("adtl"));
+        list.put(adtl);
+        return list.array();
+    }
+
     private byte[] buildHeader(long dataSize) {
         int byteRate = SAMPLE_RATE * channels * BITS_PER_SAMPLE / 8;
         int blockAlign = channels * BITS_PER_SAMPLE / 8;
@@ -269,6 +397,10 @@ public class WavRecorder {
         return buffer.array();
     }
 
+    private static byte[] intLE(int value) {
+        return ByteBuffer.allocate(4).order(ByteOrder.LITTLE_ENDIAN).putInt(value).array();
+    }
+
     private static byte[] ascii(String value) {
         return value.getBytes(StandardCharsets.US_ASCII);
     }
diff --git a/app/src/main/java/com/wuhei/reccoon/WaveformView.java b/app/src/main/java/com/wuhei/reccoon/WaveformView.java
new file mode 100644
index 0000000..de62639
--- /dev/null
+++ b/app/src/main/java/com/wuhei/reccoon/WaveformView.java
@@ -0,0 +1,94 @@
+package com.wuhei.reccoon;
+
+import android.content.Context;
+import android.graphics.Canvas;
+import android.graphics.Paint;
+import android.util.AttributeSet;
+import android.view.View;
+
+import androidx.annotation.Nullable;
+
+/**
+ * A scrolling waveform of the left/mono channel. Columns whose peak reaches
+ * full scale are drawn in red so clipping is easy to spot.
+ */
+public class WaveformView extends View {
+
+    private static final int CAPACITY = 600;
+
+    private final float[] mins = new float[CAPACITY];
+    private final float[] maxs = new float[CAPACITY];
+    private final boolean[] clipped = new boolean[CAPACITY];
+
+    private final Paint wavePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
+    private final Paint clipPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
+    private final Paint centerPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
+    private final Paint backgroundPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
+
+    private int count;
+    private int writeIndex;
+
+    public WaveformView(Context context) {
+        this(context, null);
+    }
+
+    public WaveformView(Context context, @Nullable AttributeSet attrs) {
+        super(context, attrs);
+        float density = getResources().getDisplayMetrics().density;
+        wavePaint.setColor(0xFF3DDC84);
+        wavePaint.setStrokeWidth(Math.max(1f, density));
+        clipPaint.setColor(0xFFE53935);
+        clipPaint.setStrokeWidth(Math.max(1f, density));
+        centerPaint.setColor(0x33FFFFFF);
+        centerPaint.setStrokeWidth(Math.max(1f, density * 0.6f));
+        backgroundPaint.setColor(0x14000000);
+    }
+
+    /** Appends min/max pairs ({@code [min0,max0,min1,max1,...]}) to the ring. */
+    public void append(float[] waveform) {
+        if (waveform == null || waveform.length < 2) {
+            return;
+        }
+        for (int i = 0; i + 1 < waveform.length; i += 2) {
+            mins[writeIndex] = waveform[i];
+            maxs[writeIndex] = waveform[i + 1];
+            clipped[writeIndex] = Math.abs(waveform[i]) >= 0.999f
+                    || Math.abs(waveform[i + 1]) >= 0.999f;
+            writeIndex = (writeIndex + 1) % CAPACITY;
+            if (count < CAPACITY) {
+                count++;
+            }
+        }
+        invalidate();
+    }
+
+    public void reset() {
+        count = 0;
+        writeIndex = 0;
+        invalidate();
+    }
+
+    @Override
+    protected void onDraw(Canvas canvas) {
+        super.onDraw(canvas);
+        int width = getWidth();
+        int height = getHeight();
+        if (width <= 0 || height <= 0) {
+            return;
+        }
+        canvas.drawRect(0, 0, width, height, backgroundPaint);
+
+        float centerY = height / 2f;
+        canvas.drawLine(0, centerY, width, centerY, centerPaint);
+
+        float amplitude = centerY * 0.92f;
+        float step = (float) width / CAPACITY;
+        for (int i = 0; i < count; i++) {
+            int index = (writeIndex - count + i + CAPACITY) % CAPACITY;
+            float x = i * step + step / 2f;
+            float top = centerY - maxs[index] * amplitude;
+            float bottom = centerY - mins[index] * amplitude;
+            canvas.drawLine(x, top, x, bottom, clipped[index] ? clipPaint : wavePaint);
+        }
+    }
+}
diff --git a/app/src/main/res/drawable/badge_marker.xml b/app/src/main/res/drawable/badge_marker.xml
new file mode 100644
index 0000000..267ee7e
--- /dev/null
+++ b/app/src/main/res/drawable/badge_marker.xml
@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shape="rectangle">
+    <corners android:radius="14dp" />
+    <solid android:color="#2A3442" />
+    <stroke
+        android:width="1dp"
+        android:color="#3A4A5E" />
+</shape>
diff --git a/app/src/main/res/drawable/bg_record_active.xml b/app/src/main/res/drawable/bg_record_active.xml
index e218a37..4034b8c 100644
--- a/app/src/main/res/drawable/bg_record_active.xml
+++ b/app/src/main/res/drawable/bg_record_active.xml
@@ -9,10 +9,10 @@
         </shape>
     </item>
     <item
-        android:bottom="62dp"
-        android:left="62dp"
-        android:right="62dp"
-        android:top="62dp">
+        android:bottom="46dp"
+        android:left="46dp"
+        android:right="46dp"
+        android:top="46dp">
         <shape android:shape="rectangle">
             <corners android:radius="14dp" />
             <solid android:color="@color/accent" />
diff --git a/app/src/main/res/drawable/bg_record_idle.xml b/app/src/main/res/drawable/bg_record_idle.xml
index c9f776a..0a6be67 100644
--- a/app/src/main/res/drawable/bg_record_idle.xml
+++ b/app/src/main/res/drawable/bg_record_idle.xml
@@ -9,10 +9,10 @@
         </shape>
     </item>
     <item
-        android:bottom="56dp"
-        android:left="56dp"
-        android:right="56dp"
-        android:top="56dp">
+        android:bottom="42dp"
+        android:left="42dp"
+        android:right="42dp"
+        android:top="42dp">
         <shape android:shape="oval">
             <solid android:color="@color/accent" />
         </shape>
diff --git a/app/src/main/res/layout/activity_main.xml b/app/src/main/res/layout/activity_main.xml
index f7f2ac6..8bda7d3 100644
--- a/app/src/main/res/layout/activity_main.xml
+++ b/app/src/main/res/layout/activity_main.xml
@@ -2,21 +2,22 @@
 <androidx.constraintlayout.widget.ConstraintLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
+    android:id="@+id/root"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="@color/background"
-    android:paddingLeft="24dp"
-    android:paddingRight="24dp">
+    android:paddingLeft="20dp"
+    android:paddingRight="20dp">
 
     <TextView
         android:id="@+id/titleText"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:layout_marginTop="24dp"
+        android:layout_marginTop="16dp"
         android:letterSpacing="0.04"
         android:text="@string/app_name"
         android:textColor="@color/text_primary"
-        android:textSize="32sp"
+        android:textSize="30sp"
         android:textStyle="bold"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintStart_toStartOf="parent"
@@ -26,7 +27,7 @@
         android:id="@+id/libraryButton"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:layout_marginTop="16dp"
+        android:layout_marginTop="8dp"
         android:layout_marginEnd="4dp"
         android:background="?android:attr/selectableItemBackground"
         android:padding="8dp"
@@ -40,19 +41,18 @@
         android:id="@+id/subtitleText"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:layout_marginTop="2dp"
         android:text="@string/subtitle"
         android:textColor="@color/text_secondary"
-        android:textSize="13sp"
+        android:textSize="12sp"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toBottomOf="@id/titleText" />
 
     <ImageView
         android:id="@+id/recIndicator"
-        android:layout_width="14dp"
-        android:layout_height="14dp"
-        android:layout_marginBottom="8dp"
+        android:layout_width="12dp"
+        android:layout_height="12dp"
+        android:layout_marginBottom="6dp"
         android:contentDescription="@null"
         android:src="@drawable/ic_rec_dot"
         android:visibility="invisible"
@@ -64,11 +64,11 @@
         android:id="@+id/timerText"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:layout_marginBottom="14dp"
+        android:layout_marginBottom="10dp"
         android:fontFamily="monospace"
         android:text="@string/timer_zero"
         android:textColor="@color/text_primary"
-        android:textSize="52sp"
+        android:textSize="46sp"
         android:textStyle="bold"
         app:layout_constraintBottom_toTopOf="@id/recordButton"
         app:layout_constraintEnd_toEndOf="parent"
@@ -76,8 +76,8 @@
 
     <ImageButton
         android:id="@+id/recordButton"
-        android:layout_width="180dp"
-        android:layout_height="180dp"
+        android:layout_width="148dp"
+        android:layout_height="148dp"
         android:background="@drawable/bg_record_idle"
         android:contentDescription="@string/cd_record"
         android:scaleType="centerInside"
@@ -86,51 +86,91 @@
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toTopOf="parent"
-        app:layout_constraintVertical_bias="0.42" />
+        app:layout_constraintVertical_bias="0.34" />
+
+    <com.wuhei.reccoon.WaveformView
+        android:id="@+id/waveformView"
+        android:layout_width="0dp"
+        android:layout_height="64dp"
+        android:layout_marginTop="16dp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/recordButton" />
 
     <com.wuhei.reccoon.LevelMeterView
         android:id="@+id/levelMeter"
         android:layout_width="0dp"
-        android:layout_height="46dp"
-        android:layout_marginTop="22dp"
+        android:layout_height="38dp"
+        android:layout_marginTop="10dp"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintStart_toStartOf="parent"
-        app:layout_constraintTop_toBottomOf="@id/recordButton" />
+        app:layout_constraintTop_toBottomOf="@id/waveformView" />
 
-    <androidx.appcompat.widget.AppCompatCheckBox
-        android:id="@+id/silenceCheckbox"
+    <Button
+        android:id="@+id/markButton"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:layout_marginTop="10dp"
-        android:text="@string/silence_recording"
-        android:textColor="@color/text_secondary"
-        android:textSize="13sp"
+        android:layout_marginTop="6dp"
+        android:enabled="false"
+        android:minWidth="140dp"
+        android:text="@string/mark_action"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toBottomOf="@id/levelMeter" />
 
+    <LinearLayout
+        android:id="@+id/optionsRow"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="2dp"
+        android:gravity="center"
+        android:orientation="horizontal"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/markButton">
+
+        <androidx.appcompat.widget.AppCompatCheckBox
+            android:id="@+id/monoCheckbox"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:contentDescription="@string/mono_recording"
+            android:text="@string/mono_short"
+            android:textColor="@color/text_secondary"
+            android:textSize="13sp" />
+
+        <androidx.appcompat.widget.AppCompatCheckBox
+            android:id="@+id/silenceCheckbox"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginStart="10dp"
+            android:contentDescription="@string/silence_recording"
+            android:text="@string/silence_short"
+            android:textColor="@color/text_secondary"
+            android:textSize="13sp" />
+    </LinearLayout>
+
     <TextView
         android:id="@+id/statusText"
         android:layout_width="0dp"
         android:layout_height="wrap_content"
-        android:layout_marginTop="14dp"
+        android:layout_marginTop="8dp"
         android:gravity="center"
         android:text="@string/status_idle"
         android:textColor="@color/text_secondary"
-        android:textSize="15sp"
+        android:textSize="14sp"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintStart_toStartOf="parent"
-        app:layout_constraintTop_toBottomOf="@id/silenceCheckbox" />
+        app:layout_constraintTop_toBottomOf="@id/optionsRow" />
 
     <TextView
         android:id="@+id/footerText"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:layout_marginBottom="12dp"
+        android:layout_marginBottom="10dp"
         android:alpha="0.6"
         android:text="@string/footer"
         android:textColor="@color/text_secondary"
-        android:textSize="12sp"
+        android:textSize="11sp"
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintStart_toStartOf="parent" />
diff --git a/app/src/main/res/layout/activity_player.xml b/app/src/main/res/layout/activity_player.xml
index 479efa9..67f5284 100644
--- a/app/src/main/res/layout/activity_player.xml
+++ b/app/src/main/res/layout/activity_player.xml
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/root"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="@color/background"
@@ -74,6 +75,36 @@
                 android:text="@string/player_speed_1x" />
         </LinearLayout>
 
+        <LinearLayout
+            android:id="@+id/markersSection"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="14dp"
+            android:orientation="vertical"
+            android:visibility="gone">
+
+            <TextView
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:text="@string/markers_title"
+                android:textColor="@color/text_primary"
+                android:textSize="15sp"
+                android:textStyle="bold" />
+
+            <HorizontalScrollView
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:layout_marginTop="6dp"
+                android:scrollbars="none">
+
+                <LinearLayout
+                    android:id="@+id/markersContainer"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:orientation="horizontal" />
+            </HorizontalScrollView>
+        </LinearLayout>
+
         <View
             android:layout_width="match_parent"
             android:layout_height="1dp"
diff --git a/app/src/main/res/layout/activity_recordings.xml b/app/src/main/res/layout/activity_recordings.xml
index c0ad20a..aff2088 100644
--- a/app/src/main/res/layout/activity_recordings.xml
+++ b/app/src/main/res/layout/activity_recordings.xml
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/root"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="@color/background"
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index b08c3f7..54a69d9 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -1,9 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
     <string name="app_name">RECCoon</string>
-    <string name="subtitle">by wuhei · v1.2.0-alpha</string>
+    <string name="subtitle">by wuhei · v1.3.0-alpha</string>
     <string name="timer_zero">00:00</string>
-    <string name="footer">44.1 kHz · 16-bit · stereo PCM (WAV)</string>
+    <string name="footer">44.1 kHz · 16-bit · PCM (WAV) · cue markers</string>
 
     <string name="status_idle">Tap the button to start recording</string>
     <string name="status_recording">Recording… tap again to stop and save</string>
@@ -12,6 +12,17 @@
     <string name="cd_record">Start recording</string>
     <string name="cd_stop">Stop and save</string>
 
+    <string name="mark_action">Mark</string>
+    <string name="marker_title">Add marker</string>
+    <string name="marker_hint">Marker label</string>
+    <string name="marker_add">Add</string>
+    <string name="marker_fmt">Marker %1$d</string>
+    <string name="marker_added_fmt">Marker %1$d added</string>
+    <string name="markers_title">Markers</string>
+
+    <string name="mono_short">Mono</string>
+    <string name="mono_recording">Record in mono (half file size)</string>
+    <string name="silence_short">Silence alerts</string>
     <string name="silence_recording">Silence notifications &amp; vibrations while recording</string>
     <string name="dnd_title">Allow Do Not Disturb</string>
     <string name="dnd_message">To silence notifications and vibrations while recording, allow RECCoon access to Do Not Disturb.</string>