fix: playhead drift, replay, and cursor flicker; add selection transport

**Playhead ran ahead of the audio.** It was dead-reckoned by summing
GetFrameTime() every frame, so every frame's *render* work counted as
playback time and the error compounded — by seconds over a long region,
and worst when zoomed out where each frame does the most work. That is why
it tracked fine zoomed in. It is now derived from a wall-clock instant
captured when the buffer is handed to the device, so it cannot drift from
the audio regardless of frame timing.

**Replay after a natural finish left the marker stuck at the end.** The
rail's play button never cleared playbackFinished, so the stale
playheadT > 1.0 persisted and DrawPlayhead early-returned while the audio
played from the top. The Space path already handled this; the button did
not.

**No way to replay a subrange.** The playhead is now drawn while stopped
(with a grab tab) and can be dragged to set where the next play starts
*within* the selection, leaving the region itself intact. Stopping parks
the marker where it stopped rather than snapping to the start.

playheadT is a fraction of the *played* span, which stops being the
selection once a scrub offset exists — so every conversion goes through
absolute file time, the only frame the two share. Getting this wrong made
stop-after-scrub jump backwards.

**Selection transport bar.** Rewind / play-pause / stop / loop, attached
above the selection box. Pause resumes where it left off; loop restarts
from the top of the region rather than repeating whatever tail the last
play started from.

**Cursor flicker.** Twelve unconditional SetMouseCursor calls ran per
frame and the last one won. Two blocks in particular both ran every frame:
one set a cursor regardless of mouse position, and a second overrode it
only when the mouse was inside the spectrogram — so when a capture guard
had parked mousePos off-screen, the first block's stale choice stuck. That
is the fight between finger/pointer, resize/pointer and crosshair/pointer.
Handlers now record a prioritised request (active drag > hover hint >
default) and it is applied once at the end of the frame. The divider hint
is RESIZE_NS rather than the 4-way arrow while here.

The rewind glyph drew its bar and triangle with a gap between them and read
as a lone vertical bar; verified the fix by rendering it offscreen and
dumping pixels rather than eyeballing the geometry.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V8ZWfr5XZyyDttvkhJUgHN

README.md

@@ -44,10 +44,15 @@ format.
 - **mLnL annotation overlay** — labelled boxes from the WAV's embedded annotation
   chunk; hover a box (or its region on the scope) for per-frame detail (sequence,
   channel, rate, scheduling offset…).
-- **Zoom & pan** the time/frequency view.
+- **Zoom & pan** the time/frequency view, with a **minimap** for navigating a
+  long capture without zooming out and back in.
+- **Collision detection** — finds transmissions that genuinely overlap in *both*
+  time and frequency, and jumps between them.
 - **Region selection** — box a time *and* frequency range with the mouse.
 - **Filtered playback** — play just the selected region, band-limited to the
   selected frequency box via an FFT bandpass. What you hear is what you'd export.
+  Transport controls (play/pause, rewind, loop) attach to the selection, and the
+  playhead can be dragged to replay a subrange.
 - **Waveform scope** — toggleable time-domain view beneath the spectrum.
 - **Marker / ruler** and a **spectrum slice (PSD)** readout.
 - **Export** — save the view as a PNG, or the selected region as a WAV.
@@ -141,6 +146,7 @@ Middle-drag always pans.
 | **Ctrl+wheel** | Zoom the frequency axis only |
 | **Wheel on a scrollbar** | Pan that axis (**Shift** to zoom it) |
 | **Space** | Play / stop the selected region |
+| **Drag the playhead** | (while stopped) set where the next play starts |
 | **Hover an annotation** | Tooltip with that frame's mLnL detail; lists **every** overlapping frame under the cursor |
 | **N** / **Shift+N** | Jump to the next / previous collision |
 | **O** | Open file browser |
@@ -180,6 +186,17 @@ texture and only rebuilt when its *content* changes (new file, colormap,
 overlays toggled); panning and zooming just move the rectangle drawn on top, so
 navigation costs nothing.
 
+### Playback
+
+**Space** plays the selected region, band-limited to the selected frequency box.
+Selecting a region also brings up a small transport bar above it — rewind,
+play/pause, stop, and loop. Pause resumes where it left off; loop repeats the
+whole region.
+
+While stopped, the playhead stays where it is and can be dragged: that sets
+where the next play begins *within* the selection, so a subrange can be replayed
+without redrawing the region. Clearing or redrawing the selection resets it.
+
 ### Inspecting overlapping transmissions
 
 When several stations are on the air at once their annotation boxes stack, and
@@ -255,25 +272,10 @@ Annotation kinds: `tx_frame`, `tx_burst`, `control`, `channel_up`,
 
 ## Driving the GUI headlessly (agents / CI)
 
-The app can be run, screenshotted, and clicked on a virtual X display with no
+The app runs, screenshots, and takes synthetic input on a virtual X display with
-monitor or GPU (Mesa software GL under Xvfb). The full playbook lives in
+no monitor or GPU (Mesa software GL under Xvfb). The playbook is in
-[`AGENTS.md`](AGENTS.md); the working reference implementation is
+[`AGENTS.md`](AGENTS.md); [`shot_input.sh`](shot_input.sh) is the working
-[`shot_input.sh`](shot_input.sh).
+reference implementation.
-
-The loop in one breath:
-
-```bash
-Xvfb :99 -screen 0 1280x800x24 >/tmp/xvfb.log 2>&1 &     # 1. fake screen
-DISPLAY=:99 ./bin/Debug/rspektrum mlnl_samples.wav \
-        >/tmp/app.log 2>&1 &                              # 2. run on it
-sleep 2                                                    # 3. reach a steady frame
-DISPLAY=:99 import -window root /tmp/shot.png             # 4. grab the frame
-```
-
-Prerequisites (Debian/Ubuntu): `sudo apt-get install xvfb imagemagick xdotool`
-(plus `libgl1-mesa-dri` and `LIBGL_ALWAYS_SOFTWARE=1` if GL fails / frames are
-black). Synthesize input with `xdotool` against `DISPLAY=:99` to exercise UI
-paths.
 
 ---
 

src/audio.c

@@ -195,8 +195,16 @@ static float* BuildSelectionAudio(int* outNumSamples)
 {
     if (!app.loaded || !app.stftComputed) return NULL;
 
-    int startSample = (int)(app.sel.timeStart * app.signal.numSamples);
+    // playFromT lets playback begin partway into the selection (the user
-    int endSample = (int)(app.sel.timeEnd * app.signal.numSamples);
+    // scrubbed the playhead) without disturbing the selection itself — the
+    // whole point is to replay a subrange while keeping the region intact.
+    float t0 = app.sel.timeStart;
+    float t1 = app.sel.timeEnd;
+    if (app.playFromT > 0.0f && app.playFromT < 1.0f)
+        t0 = t0 + app.playFromT * (t1 - t0);
+
+    int startSample = (int)(t0 * app.signal.numSamples);
+    int endSample = (int)(t1 * app.signal.numSamples);
     int numSamples = endSample - startSample;
     if (numSamples <= 0 || startSample < 0 || endSample > app.signal.numSamples) return NULL;
 
@@ -246,10 +254,20 @@ void PlaySelectedRegion(void)
     // Snapshot what we're about to play so the playhead tracks THIS region even
     // if the user moves the selection mid-playback. Duration comes from the
     // buffer we actually built, not from app.signal.duration.
+    // Snapshot the span actually handed to the device, which is the selection
+    // narrowed by any scrub offset — the playhead is measured against this.
     app.playSelStart = app.sel.timeStart;
     app.playSelEnd   = app.sel.timeEnd;
+    if (app.playFromT > 0.0f && app.playFromT < 1.0f)
+        app.playSelStart += app.playFromT * (app.sel.timeEnd - app.sel.timeStart);
     app.playDuration = (app.signal.sampleRate > 0)
                      ? (float)numSamples / (float)app.signal.sampleRate : 0.0f;
+    // Anchor the playhead to the wall clock (see playStartTime). Set here, at
+    // the moment the buffer is handed to the device, so the marker can't drift
+    // from the audio no matter how long a frame takes.
+    app.playStartTime = GetTime();
+    app.playheadSeekT = 0.0f;
+    app.playheadT     = 0.0f;
 
     EnsureAudioDevice();  // opened on demand; released again once playback ends
     if (AudioPlaybackSound.frameCount != 0) UnloadSound(AudioPlaybackSound);

src/render.c

@@ -2,6 +2,7 @@
 #include "render.h"
 #include "stft.h"   // ComputeSpectralStats for the selection panel
 #include "utils.h"  // ComputeSignalStats
+#include "audio.h"  // PlaySelectedRegion for the selection transport
 
 #include <math.h>
 #include <stdlib.h>
@@ -579,6 +580,181 @@ static void DrawStatPanel(Rectangle bounds, Rectangle sel)
     }
 }
 
+
+// ===== Selection transport bar =====
+// Play controls attached to the selection box, so the common actions are where
+// the user is already looking instead of over on the rail. Appears only when a
+// region is selected.
+//
+// Geometry is split from drawing (SelectionTransportRect / TransportButtonRect)
+// because input handling runs long before the draw pass, and a click here must
+// be claimed before the pan/select handlers see it.
+
+// Number of buttons: rewind-to-start, play/pause, stop, loop.
+#define TRANSPORT_BUTTONS 4
+
+Rectangle SelectionTransportRect(Rectangle bounds)
+{
+    bool hasSelection = (app.sel.timeStart > 0.001f || app.sel.timeEnd < 0.999f ||
+                         app.sel.freqStart > 0.001f || app.sel.freqEnd < 0.999f);
+    if (!app.loaded || !hasSelection || app.sel.isTimeSelecting || app.sel.isDragging)
+        return (Rectangle){ 0, 0, 0, 0 };
+
+    float scale = GetUIScale();
+    float bw = 26.0f * scale;                       // per-button
+    float w  = bw * TRANSPORT_BUTTONS + 8.0f * scale;
+    float h  = 24.0f * scale;
+
+    float viewWidth = app.view.end - app.view.start;
+    if (viewWidth <= 0.0f) return (Rectangle){ 0, 0, 0, 0 };
+    float x0 = bounds.x + ((app.sel.timeStart - app.view.start) / viewWidth) * bounds.width;
+    float x1 = bounds.x + ((app.sel.timeEnd   - app.view.start) / viewWidth) * bounds.width;
+
+    float freqWidth = app.view.freqEnd - app.view.freqStart;
+    float yTop = bounds.y + bounds.height -
+                 ((app.sel.freqEnd - app.view.freqStart) / freqWidth) * bounds.height;
+
+    // Centred on the selection, just above its top edge; flipped below when
+    // there isn't room, and clamped so it stays inside the viewport.
+    float cx = (fmaxf(x0, bounds.x) + fminf(x1, bounds.x + bounds.width)) * 0.5f;
+    float bx = cx - w * 0.5f;
+    float by = yTop - h - 6.0f * scale;
+    if (by < bounds.y + 2.0f) by = yTop + 6.0f * scale;
+    if (by + h > bounds.y + bounds.height) by = bounds.y + bounds.height - h - 2.0f;
+    if (bx < bounds.x) bx = bounds.x;
+    if (bx + w > bounds.x + bounds.width) bx = bounds.x + bounds.width - w;
+
+    // Off-screen selection: nothing to attach to.
+    if (x1 < bounds.x || x0 > bounds.x + bounds.width) return (Rectangle){ 0, 0, 0, 0 };
+    return (Rectangle){ bx, by, w, h };
+}
+
+static Rectangle TransportButtonRect(Rectangle bar, int i)
+{
+    float scale = GetUIScale();
+    float bw = 26.0f * scale;
+    return (Rectangle){ bar.x + 4.0f * scale + i * bw, bar.y + 2.0f * scale,
+                        bw, bar.height - 4.0f * scale };
+}
+
+bool TransportCapturesMouse(Rectangle bounds)
+{
+    Rectangle bar = SelectionTransportRect(bounds);
+    if (bar.width <= 0.0f) return false;
+    return CheckCollisionPointRec(GetMousePosition(), bar);
+}
+
+// Act on a click. Separate from drawing so it runs during the input phase.
+void UpdateSelectionTransport(Rectangle bounds)
+{
+    Rectangle bar = SelectionTransportRect(bounds);
+    if (bar.width <= 0.0f) return;
+    if (!IsMouseButtonPressed(MOUSE_LEFT_BUTTON)) return;
+
+    Vector2 m = GetMousePosition();
+    for (int i = 0; i < TRANSPORT_BUTTONS; i++) {
+        if (!CheckCollisionPointRec(m, TransportButtonRect(bar, i))) continue;
+        switch (i) {
+            case 0:  // rewind to the start of the selection
+                app.playFromT = 0.0f;
+                app.playheadT = 0.0f;
+                if (app.isPlaying) {
+                    StopSound(AudioPlaybackSound);
+                    PlaySelectedRegion();
+                    app.playbackFinished = false;
+                }
+                break;
+            case 1:  // play / pause
+                if (app.isPlaying) {
+                    // Pause: remember where we are so play resumes from here.
+                    float stopAbs = app.playSelStart +
+                                    app.playheadT * (app.playSelEnd - app.playSelStart);
+                    float selSpan = app.sel.timeEnd - app.sel.timeStart;
+                    app.playFromT = (selSpan > 1e-6f)
+                                  ? Clamp((stopAbs - app.sel.timeStart) / selSpan, 0.0f, 0.999f)
+                                  : 0.0f;
+                    StopSound(AudioPlaybackSound);
+                    app.isPlaying = false;
+                    app.playbackFinished = false;
+                } else {
+                    PlaySelectedRegion();
+                    app.isPlaying = true;
+                    app.playbackFinished = false;
+                }
+                break;
+            case 2:  // stop: halt and rewind
+                if (app.isPlaying) StopSound(AudioPlaybackSound);
+                app.isPlaying = false;
+                app.playbackFinished = false;
+                app.playFromT = 0.0f;
+                app.playheadT = 0.0f;
+                break;
+            case 3:
+                app.loopPlayback = !app.loopPlayback;
+                break;
+        }
+        break;
+    }
+}
+
+void DrawSelectionTransport(Rectangle bounds)
+{
+    Rectangle bar = SelectionTransportRect(bounds);
+    if (bar.width <= 0.0f) return;
+
+    float scale = GetUIScale();
+    Vector2 m = GetMousePosition();
+
+    DrawRectangleRec(bar, (Color){ 26, 26, 32, 235 });
+    DrawRectangleLinesEx(bar, 1, (Color){ 110, 110, 130, 255 });
+
+    for (int i = 0; i < TRANSPORT_BUTTONS; i++) {
+        Rectangle b = TransportButtonRect(bar, i);
+        bool over = CheckCollisionPointRec(m, b);
+        bool on   = (i == 3) ? app.loopPlayback : false;
+        if (over) DrawRectangleRec(b, (Color){ 60, 60, 76, 255 });
+        if (on)   DrawRectangleRec(b, (Color){ 50, 80, 60, 255 });
+
+        Color c = on ? (Color){ 150, 230, 170, 255 } : (Color){ 210, 210, 220, 255 };
+        float cx = b.x + b.width * 0.5f, cy = b.y + b.height * 0.5f;
+        float s = b.height * 0.26f;
+
+        switch (i) {
+            case 0:  // |< rewind to start
+                // Bar on the left, triangle pointing INTO it. raylib wants
+                // counter-clockwise vertices; the previous winding put the apex
+                // to the right of the base, so the triangle never rendered and
+                // this read as a lone vertical bar.
+                DrawRectangleRec((Rectangle){ cx - s, cy - s, 2.0f * scale, s * 2 }, c);
+                DrawTriangle((Vector2){ cx - s + 3 * scale, cy },
+                             (Vector2){ cx + s, cy + s },
+                             (Vector2){ cx + s, cy - s }, c);
+                break;
+            case 1:  // play / pause
+                if (app.isPlaying) {
+                    DrawRectangleRec((Rectangle){ cx - s, cy - s, s * 0.7f, s * 2 }, c);
+                    DrawRectangleRec((Rectangle){ cx + s * 0.3f, cy - s, s * 0.7f, s * 2 }, c);
+                } else {
+                    DrawTriangle((Vector2){ cx - s * 0.7f, cy - s },
+                                 (Vector2){ cx - s * 0.7f, cy + s },
+                                 (Vector2){ cx + s, cy }, c);
+                }
+                break;
+            case 2:  // stop
+                DrawRectangleRec((Rectangle){ cx - s * 0.85f, cy - s * 0.85f,
+                                              s * 1.7f, s * 1.7f }, c);
+                break;
+            case 3:  // loop
+                DrawRectangleLinesEx((Rectangle){ cx - s, cy - s * 0.7f, s * 2, s * 1.4f },
+                                     1.4f, c);
+                DrawTriangle((Vector2){ cx + s * 0.2f, cy - s * 1.3f },
+                             (Vector2){ cx + s * 0.2f, cy - s * 0.1f },
+                             (Vector2){ cx + s * 1.1f, cy - s * 0.7f }, c);
+                break;
+        }
+    }
+}
+
 void DrawSelection(Rectangle bounds)
 {
     // Only draw if selection is not full range AND not currently dragging
@@ -1395,7 +1571,11 @@ void DrawAnnotations(Rectangle bounds)
     bool mouseInBounds = CheckCollisionPointRec(m, bounds);
     bool suppressHover = app.sel.isTimeSelecting || app.sel.isFreqSelecting ||
                          app.sel.isDragging || app.view.isPanning || app.marker.dragging ||
-                         app.markerMode;
+                         app.markerMode ||
+                         // The transport bar floats over the spectrogram; an
+                         // annotation tooltip firing underneath it would cover
+                         // the buttons being reached for.
+                         TransportCapturesMouse(bounds);
 
     int hoverEvent = -1;
     // hover prefers later layers (assertions over bursts, point markers over both),
@@ -2316,21 +2496,39 @@ void DrawTimeline(Rectangle lane)
 // Playhead
 // ============================================================================
 
-void DrawPlayhead(Rectangle bounds)
+// Screen X of the playhead within `bounds`, or a negative value when there is
+// nothing to draw. Shared with the scrub hit-test so the marker and its grab
+// region can't disagree about where it is.
+float PlayheadScreenX(Rectangle bounds)
 {
-    if (!app.isPlaying || app.playheadT < 0.0f || app.playheadT > 1.0f) return;
+    if (!app.loaded || app.playheadT < 0.0f || app.playheadT > 1.0f) return -1.0f;
+    if (app.playSelEnd <= app.playSelStart) return -1.0f;
 
     // Against the snapshot of the playing region, not the live selection.
     float timePos = app.playSelStart + app.playheadT * (app.playSelEnd - app.playSelStart);
     float viewWidth = app.view.end - app.view.start;
+    if (viewWidth <= 0.0f) return -1.0f;
     float t = (timePos - app.view.start) / viewWidth;
-    float x = bounds.x + t * bounds.width;
+    return bounds.x + t * bounds.width;
+}
 
-    // Clamp to bounds
+void DrawPlayhead(Rectangle bounds)
+{
+    // Drawn while stopped too, so the marker stays put and can be dragged to
+    // replay a subrange without redoing the selection.
+    float x = PlayheadScreenX(bounds);
+    if (x < 0.0f) return;
+    if (x < bounds.x - 4 || x > bounds.x + bounds.width + 4) return;
     x = fmaxf(bounds.x, fminf(bounds.x + bounds.width, x));
 
-    // Draw vertical line
+    Color c = app.isPlaying ? RED : (Color){ 255, 120, 120, 255 };
-    DrawLine(x, bounds.y, x, bounds.y + bounds.height, RED);
+    DrawLine(x, bounds.y, x, bounds.y + bounds.height, c);
-    // Draw semi-transparent overlay to make it stand out
     DrawRectangle(x - 2, bounds.y, 4, bounds.height, (Color){ 255, 0, 0, 60 });
+
+    // Grab tab at the top, so the marker reads as draggable when stopped.
+    if (!app.isPlaying) {
+        DrawTriangle((Vector2){ x - 5, bounds.y },
+                     (Vector2){ x + 5, bounds.y },
+                     (Vector2){ x, bounds.y + 8 }, c);
+    }
 }

src/render.h

@@ -45,11 +45,23 @@ void DrawAnnotationsToImage(Image* img, Font font);
 void DrawSpectrogramGrid(Rectangle bounds, int numCellsX, int numCellsY, Color color);
 void DrawLabels(Rectangle bounds);
 void DrawSelection(Rectangle bounds);
+
+// --- Selection transport bar ---
+// Play controls attached to the selection box. Geometry and input are split
+// from drawing so a click can be claimed during the input phase, before the
+// pan/select handlers run.
+Rectangle SelectionTransportRect(Rectangle bounds);
+bool TransportCapturesMouse(Rectangle bounds);
+void UpdateSelectionTransport(Rectangle bounds);
+void DrawSelectionTransport(Rectangle bounds);
 void DrawSelectionDrag(Rectangle bounds);
 void DrawCursorReadout(Rectangle bounds);
 void DrawMarkers(Rectangle bounds);
 void DrawSpectrumPanel(Rectangle bounds);
 void DrawPlayhead(Rectangle bounds);
+// Playhead X within bounds, or <0 when there's nothing to draw. Used by the
+// scrub hit-test so the marker and its grab region agree.
+float PlayheadScreenX(Rectangle bounds);
 void DrawAnnotations(Rectangle bounds);
 
 // --- Minimap ---

src/spectrogram.c

@@ -292,7 +292,7 @@ void ResetForNewSignal(void)
     if (app.isPlaying && AudioPlaybackSound.frameCount > 0) StopSound(AudioPlaybackSound);
     app.isPlaying = false;
     app.playbackFinished = false;
-    app.playheadElapsed = 0.0f;
+    app.playheadSeekT = 0.0f;
     app.playheadT = 0.0f;
 
     // Invalidate the cached visible texture.
@@ -1097,6 +1097,11 @@ int main(int argc, char* argv[])
     {
         g_frameCounter++;
 
+        // Cursor is decided once per frame: handlers below record a request and
+        // the highest-priority one is applied at the end. Reset here.
+        app.cursorRequest = MOUSE_CURSOR_DEFAULT;
+        app.cursorPriority = -1;
+
         // Set when the window is in the background but still has compute to
         // finish: the frame runs its logic and skips presenting. See the
         // power-management block below.
@@ -1199,17 +1204,29 @@ int main(int argc, char* argv[])
         if (app.isPlaying && AudioPlaybackSound.frameCount > 0) {
             // Check if sound stopped playing (IsSoundPlaying returns false when done)
             if (!IsSoundPlaying(AudioPlaybackSound)) {
-                app.isPlaying = false;
+                if (app.loopPlayback) {
-                app.playbackFinished = true;
+                    // Restart from the top of the selection, ignoring any scrub
+                    // offset: a loop should repeat the whole region, not the
+                    // tail the last play happened to start from.
+                    app.playFromT = 0.0f;
+                    PlaySelectedRegion();
+                    app.isPlaying = true;
+                    app.playbackFinished = false;
+                } else {
+                    app.isPlaying = false;
+                    app.playbackFinished = true;
+                }
             }
-            // Track playhead position manually, against the length of the buffer
+            // Derive the playhead from the wall clock, not from summed frame
-            // that's actually playing (see playDuration) rather than a length
+            // times. Audio plays on its own clock; accumulating GetFrameTime()
-            // re-derived from the live selection — the user can move the
+            // counted every frame's render work as playback time, so the marker
-            // selection mid-playback without the marker jumping.
+            // ran ahead — by seconds on a long region, and worst when zoomed out
-            app.playheadElapsed += GetFrameTime();
+            // where each frame does the most work.
             if (app.playDuration > 0.0f) {
-                app.playheadT = app.playheadElapsed / app.playDuration;
+                double elapsed = GetTime() - app.playStartTime;
+                app.playheadT = app.playheadSeekT + (float)(elapsed / app.playDuration);
                 if (app.playheadT > 1.0f) app.playheadT = 1.0f;
+                if (app.playheadT < 0.0f) app.playheadT = 0.0f;
             }
         }
 
@@ -1233,6 +1250,43 @@ int main(int argc, char* argv[])
             float spectroHeight = L.spectroHeight;
             Rectangle viewBounds = L.viewBounds;
 
+            // Selection transport. Claims its clicks before the pan/select
+            // handlers below, which are gated on TransportCapturesMouse().
+            UpdateSelectionTransport(viewBounds);
+
+            // Playhead scrub. Only while stopped: dragging the marker sets
+            // where the next play starts within the selection, so a subrange
+            // can be replayed without redrawing the region. Claims the press
+            // ahead of the pan handler, which is gated on playheadDragging.
+            if (!app.isPlaying && app.loaded && app.playSelEnd > app.playSelStart) {
+                float phx = PlayheadScreenX(viewBounds);
+                Vector2 pm = GetMousePosition();
+                bool nearPlayhead = phx >= 0.0f && fabsf(pm.x - phx) <= 6.0f * viewScale &&
+                                    CheckCollisionPointRec(pm, viewBounds);
+                if (nearPlayhead && IsMouseButtonPressed(MOUSE_LEFT_BUTTON))
+                    app.playheadDragging = true;
+                if (!IsMouseButtonDown(MOUSE_LEFT_BUTTON)) app.playheadDragging = false;
+
+                if (app.playheadDragging) {
+                    RequestCursor(MOUSE_CURSOR_RESIZE_EW, CURSOR_PRI_ACTIVE);
+                    // Screen X -> time -> fraction of the SELECTION, which is
+                    // what playFromT means.
+                    float vt = (pm.x - viewBounds.x) / viewBounds.width;
+                    float tAbs = app.view.start + vt * (app.view.end - app.view.start);
+                    float selSpan = app.sel.timeEnd - app.sel.timeStart;
+                    if (selSpan > 1e-6f) {
+                        app.playFromT = Clamp((tAbs - app.sel.timeStart) / selSpan, 0.0f, 1.0f);
+                        // Keep the drawn marker under the cursor: it is measured
+                        // against playSelStart/End, not the selection.
+                        app.playSelStart = app.sel.timeStart;
+                        app.playSelEnd   = app.sel.timeEnd;
+                        app.playheadT    = app.playFromT;
+                    }
+                } else if (nearPlayhead) {
+                    RequestCursor(MOUSE_CURSOR_RESIZE_EW, CURSOR_PRI_HOVER);
+                }
+            }
+
             // Minimap scrub. Runs BEFORE the pan/zoom handlers below so a press
             // inside the minimap is claimed here; those handlers are gated on
             // MinimapCapturesMouse() and will skip it. Both writing app.view in
@@ -1335,7 +1389,8 @@ int main(int argc, char* argv[])
             // Never start a pan on a click that belongs to the UI chrome.
             bool overView = CheckCollisionPointRec(GetMousePosition(), viewBounds) &&
                             !MenubarCapturesMouse() && !SidebarCapturesMouse() &&
-                            !MinimapCapturesMouse();
+                            !MinimapCapturesMouse() && !app.playheadDragging &&
+                            !TransportCapturesMouse(viewBounds);
             if (overView && ((canPan && IsMouseButtonPressed(MOUSE_LEFT_BUTTON)) ||
                              IsMouseButtonPressed(MOUSE_BUTTON_MIDDLE))) {
                 app.view.isPanning = true;
@@ -1574,8 +1629,20 @@ int main(int argc, char* argv[])
                 StopSound(AudioPlaybackSound);
                 app.isPlaying = false;
                 app.playbackFinished = false;
-                app.playheadElapsed = 0;
+                // Leave the marker where playback stopped rather than snapping it
-                app.playheadT = 0;
+                // to the start: it stays grabbable, and the next play resumes
+                // from here. playheadT is a fraction of the PLAYED span, which is
+                // not the selection once a scrub offset is in play — convert
+                // through absolute file time, the only frame the two share.
+                {
+                    float stopAbs = app.playSelStart +
+                                    app.playheadT * (app.playSelEnd - app.playSelStart);
+                    float selSpan = app.sel.timeEnd - app.sel.timeStart;
+                    app.playFromT = (selSpan > 1e-6f)
+                                  ? Clamp((stopAbs - app.sel.timeStart) / selSpan, 0.0f, 0.999f)
+                                  : 0.0f;
+                }
+                app.playheadSeekT = 0.0f;
             } else if (app.playbackFinished) {
                 // Playback finished naturally - restart from beginning
                 PlaySelectedRegion();
@@ -1622,7 +1689,8 @@ int main(int argc, char* argv[])
         // Parking the cursor off-screen is enough to make every hit test below
         // miss without threading a flag through each one.
         if (MenubarCapturesMouse() || SidebarCapturesMouse() ||
-            MinimapCapturesMouse()) mousePos = (Vector2){ -1000, -1000 };
+            MinimapCapturesMouse() || app.playheadDragging ||
+            TransportCapturesMouse(selBounds)) mousePos = (Vector2){ -1000, -1000 };
 
 
         // Calculate divider screen position (for hover detection)
@@ -1670,39 +1738,28 @@ int main(int argc, char* argv[])
             }
         }
         
-        // Set cursor based on context
-        if (app.sel.isDragging) {
-            SetMouseCursor(MOUSE_CURSOR_RESIZE_ALL);  // 4-way arrow while dragging
-        } else if (hoverInsideSelection) {
-            SetMouseCursor(MOUSE_CURSOR_POINTING_HAND);  // Pointing hand on hover
-        } else {
-            SetMouseCursor(MOUSE_CURSOR_DEFAULT);  // Normal arrow
-        }
-
         // LMB drag = box select (time + frequency) OR drag existing selection
         if (app.loaded && !UiModalOpen() && CheckCollisionPointRec(mousePos, selBounds)) {
-            // Set cursor to resize all when near divider
+            // Cursor for the spectrogram area. One decision, stated as a
-            if (mouseNearDivider && !app.isDividing) {
+            // request — a second block used to run unconditionally before this
-                SetMouseCursor(MOUSE_CURSOR_RESIZE_ALL);
+            // one and the two disagreed, which is what made the shape flicker.
-            } else if (app.sel.isDragging) {
+            if (app.sel.isDragging || app.view.isPanning) {
-                SetMouseCursor(MOUSE_CURSOR_RESIZE_ALL);  // 4-way arrow while dragging
+                RequestCursor(MOUSE_CURSOR_RESIZE_ALL, CURSOR_PRI_ACTIVE);
+            } else if (mouseNearDivider && !app.isDividing) {
+                RequestCursor(MOUSE_CURSOR_RESIZE_NS, CURSOR_PRI_HOVER);
             } else if (hoverInsideSelection && selSelects) {
-                SetMouseCursor(MOUSE_CURSOR_POINTING_HAND);  // Pointing hand on hover
+                RequestCursor(MOUSE_CURSOR_POINTING_HAND, CURSOR_PRI_HOVER);
             } else if (selSelects) {
                 // Crosshair whenever a left-drag would draw a box, so the two
                 // gestures are distinguishable without guessing.
-                SetMouseCursor(MOUSE_CURSOR_CROSSHAIR);
+                RequestCursor(MOUSE_CURSOR_CROSSHAIR, CURSOR_PRI_HOVER);
-            } else if (app.view.isPanning) {
-                SetMouseCursor(MOUSE_CURSOR_RESIZE_ALL);
-            } else {
-                SetMouseCursor(MOUSE_CURSOR_DEFAULT);  // Normal arrow
             }
 
             if (app.markerMode) {
                 // Marker/ruler mode: LMB press drops point A, dragging moves B,
                 // release finalizes. Alt / middle-drag still pans (handled
                 // above), so don't drop a marker while panning.
-                SetMouseCursor(MOUSE_CURSOR_CROSSHAIR);
+                RequestCursor(MOUSE_CURSOR_CROSSHAIR, CURSOR_PRI_HOVER);
                 bool altPan = IsKeyDown(KEY_LEFT_ALT) || IsKeyDown(KEY_RIGHT_ALT) ||
                               IsMouseButtonDown(MOUSE_BUTTON_MIDDLE);
                 if (!altPan) {
@@ -1734,6 +1791,7 @@ int main(int argc, char* argv[])
                     app.sel.isTimeSelecting = true;
                     app.sel.isFreqSelecting = true;
                     app.sel.selectStartPos = mousePos;
+                    app.playFromT = 0.0f;   // new region plays from its start
                     
                     // Convert screen position to signal coordinates (accounting for zoom)
                     float viewportT = (mousePos.x - selBounds.x) / selBounds.width;
@@ -2142,6 +2200,7 @@ int main(int argc, char* argv[])
             if (L.timelineHeight > 0) DrawTimeline(L.timelineBounds);
             DrawAnnotations(viewBounds);
             DrawSelection(viewBounds);
+            DrawSelectionTransport(viewBounds);
             DrawSelectionDrag(viewBounds);
             DrawMarkers(viewBounds);
             DrawPlayhead(viewBounds);
@@ -2276,6 +2335,9 @@ int main(int argc, char* argv[])
             if (app.exportMessageTimer <= 0.0f) app.exportMessage[0] = '\0';
         }
 
+        // Apply the frame's cursor decision (see RequestCursor).
+        SetMouseCursor(app.cursorRequest);
+
         EndDrawing();
     }
 

src/spectrogram_types.h

@@ -202,7 +202,28 @@ typedef struct {
 
     // Playback state
     float playheadT;           // 0-1 normalized position within the PLAYING region
-    float playheadElapsed;     // Elapsed seconds since play started
+    // Wall-clock instant (GetTime()) at which the current buffer started
+    // playing. The playhead is derived from this rather than accumulated per
+    // frame: summing GetFrameTime() drifts, because every frame spent on
+    // rendering work is counted as playback time, and the error compounds over
+    // a long region. Audio runs on its own clock, so the playhead has to as
+    // well. Offset by playheadSeekT when the user scrubs.
+    double playStartTime;
+    float playheadSeekT;       // 0-1 offset into the buffer that playback began at
+    // Where the next play should start within the selection (0-1). Set by
+    // dragging the playhead while stopped; reset once the selection changes.
+    float playFromT;
+    bool playheadDragging;
+    // Repeat the selection when it reaches the end, instead of stopping.
+    bool loopPlayback;
+
+    // Mouse cursor requested for this frame, applied once at the end of it.
+    // Several handlers have an opinion about the cursor and they run in
+    // sequence, each calling SetMouseCursor unconditionally — so whichever ran
+    // last won, and two of them disagreeing produced a visible flicker between
+    // shapes. Handlers now record a request and the highest-priority one wins.
+    int cursorRequest;
+    int cursorPriority;
 
     // Snapshot of the region actually handed to the audio device, captured at
     // PlaySelectedRegion time. The playhead must be measured against this, not
@@ -449,11 +470,30 @@ static inline bool UiModalOpen(void)
     return app.showFileBrowser || app.showAbout;
 }
 
+// Request a mouse cursor for this frame. Higher priority wins; ties go to the
+// first caller. Applied once per frame (see the end of the main loop), so
+// handlers can state their preference without fighting each other.
+static inline void RequestCursor(int shape, int priority)
+{
+    if (priority > app.cursorPriority) {
+        app.cursorPriority = priority;
+        app.cursorRequest = shape;
+    }
+}
+
+// Cursor priorities: an active drag outranks a hover hint, which outranks the
+// default. Keeps "what am I doing" ahead of "what could I do".
+#define CURSOR_PRI_DEFAULT  0
+#define CURSOR_PRI_HOVER    10
+#define CURSOR_PRI_ACTIVE   20
+
 // Reset the box selection to the full signal (the "no selection" state).
 static inline void ClearSelection(void)
 {
     app.sel.timeStart = 0.0f; app.sel.timeEnd = 1.0f;
     app.sel.freqStart = 0.0f; app.sel.freqEnd = 1.0f;
+    // A scrub offset is meaningless against a selection that no longer exists.
+    app.playFromT = 0.0f;
 }
 
 // Effective top of the displayed frequency axis (Hz). Capped at the actual

src/ui.c

@@ -873,11 +873,27 @@ void DrawSidebar(void)
             StopSound(AudioPlaybackSound);
             app.isPlaying = false;
             app.playbackFinished = false;
-            app.playheadElapsed = 0;
+            // Leave the marker where playback stopped rather than snapping it
-            app.playheadT = 0;
+            // to the start: it stays grabbable, and the next play resumes
+            // from here. playheadT is a fraction of the PLAYED span, which is
+            // not the selection once a scrub offset is in play — convert
+            // through absolute file time, the only frame the two share.
+            {
+                float stopAbs = app.playSelStart +
+                                app.playheadT * (app.playSelEnd - app.playSelStart);
+                float selSpan = app.sel.timeEnd - app.sel.timeStart;
+                app.playFromT = (selSpan > 1e-6f)
+                              ? Clamp((stopAbs - app.sel.timeStart) / selSpan, 0.0f, 0.999f)
+                              : 0.0f;
+            }
+            app.playheadSeekT = 0.0f;
         } else {
             PlaySelectedRegion();
             app.isPlaying = true;
+            // Must clear: PlaySelectedRegion restarts from the top, and leaving
+            // this set left the playhead parked at the end of the previous run
+            // while the audio played from the beginning.
+            app.playbackFinished = false;
         }
     }
     y += btn + gap;