feat: Add timeline shifting and track start time editing

Implements two new editing features to provide more granular control over the CUE sheet.

app.py

@@ -132,7 +132,7 @@ def parse_cue_and_update_ui(cue_text):
     return cue_text, audio_filename, times, audio_duration, gr.update(choices=track_labels, value=[]), gr.update(visible=True)
 
 def update_editing_tools(selected_tracks, current_times, audio_duration):
-    """Dynamically shows/hides Merge or Split tools based on selection count."""
+    """Dynamically shows/hides editing tools based on selection count."""
     num_selected = len(selected_tracks)
     
     if num_selected == 1:
@@ -149,33 +149,27 @@ def update_editing_tools(selected_tracks, current_times, audio_duration):
         new_min_time = start_time + padding
         new_max_time = end_time
 
-        # --- 3. [CORRECTION] Check if the track is too short to be split ---
-        if new_min_time >= new_max_time:
-            # If the track is too short, splitting is not possible. Hide the tools.
-            return (
-                gr.update(visible=False), # Hide Merge button
-                gr.update(visible=False), # Hide Split Group
-                None,
-                None
-            )
-
+        split_possible = new_min_time < new_max_time
         # --- 4. Configure and show the Split UI with the corrected range ---
         mid_point = start_time + (end_time - start_time) / 2
         
+        current_start_time_str = seconds_to_cue_time(start_time)
+        
         return (
             gr.update(visible=False), # Hide Merge button
-            gr.update(visible=True),  # Show Split Group
-            # Use the new padded min/max values for the slider
+            gr.update(visible=split_possible),  # Show/Hide Split Group
+            gr.update(visible=True), # Show Edit Time Group
             gr.update(minimum=new_min_time, maximum=new_max_time, value=mid_point), # Configure Slider 
-            gr.update(value=f"Split at: {seconds_to_cue_time(mid_point)}") # Update slider label
+            gr.update(value=f"Split at: {seconds_to_cue_time(mid_point)}"), # Update slider label
+            gr.update(value=current_start_time_str) # Set current start time in edit box
         )
         
     elif num_selected > 1:
         # Show Merge UI
-        return gr.update(visible=True), gr.update(visible=False), None, None
+        return gr.update(visible=True), gr.update(visible=False), gr.update(visible=False), None, None, None
     else:
         # Hide everything
-        return gr.update(visible=False), gr.update(visible=False), None, None
+        return gr.update(visible=False), gr.update(visible=False), gr.update(visible=False), None, None, None
 
 def perform_manual_merge(selected_tracks, original_times, audio_duration, audio_filename):
     """Merges selected tracks. The internal logic is robust and unchanged."""
@@ -217,6 +211,51 @@ def perform_manual_split(split_time_sec, original_times, audio_duration, audio_f
     new_track_labels = generate_track_labels(new_times, audio_duration)
     return final_cue_text, new_times, gr.update(choices=new_track_labels, value=[])
 
+# --- Timeline Shift ---
+def shift_timeline(shift_amount_sec, original_times, audio_duration, audio_filename):
+    """Shifts all track start times by a specified amount."""
+    if not original_times:
+        raise gr.Error("No track times to shift.")
+    
+    # Apply the shift, ensuring no time is negative or exceeds audio duration
+    new_times = [min(max(0, t + shift_amount_sec), audio_duration) for t in original_times]
+    
+    # Clean up by sorting and removing duplicates (e.g., if multiple tracks are clamped to 0)
+    new_times = sorted(list(set(new_times)))
+    
+    final_cue_text = format_cue_text(new_times, audio_filename)
+    new_track_labels = generate_track_labels(new_times, audio_duration)
+    return final_cue_text, new_times, gr.update(choices=new_track_labels, value=[])
+
+
+# --- Edit Track Start Time ---
+def edit_track_start_time(selected_track, new_time_str, original_times, audio_duration, audio_filename):
+    """Edits the start time of a single selected track."""
+    if not selected_track:
+        raise gr.Error("No track selected for editing.")
+        
+    new_time_sec = parse_cue_time_to_seconds(new_time_str)
+    if new_time_sec is None:
+        raise gr.Error("Invalid time format. Please use MM:SS:FF.")
+
+    track_idx = int(selected_track[0].split(' ')[1]) - 1
+
+    # Boundary checks
+    prev_track_time = original_times[track_idx - 1] if track_idx > 0 else -1
+    next_track_time = original_times[track_idx + 1] if track_idx < len(original_times) - 1 else audio_duration + 1
+
+    if new_time_sec <= prev_track_time:
+        raise gr.Error(f"New time cannot be earlier than the previous track's start time ({seconds_to_cue_time(prev_track_time)}).")
+    if new_time_sec >= next_track_time:
+        raise gr.Error(f"New time cannot be later than the next track's start time ({seconds_to_cue_time(next_track_time)}).")
+
+    new_times = original_times[:]
+    new_times[track_idx] = new_time_sec
+    
+    final_cue_text = format_cue_text(new_times, audio_filename)
+    new_track_labels = generate_track_labels(new_times, audio_duration)
+    return final_cue_text, new_times, gr.update(choices=new_track_labels, value=[])
+
 
 # --- Gradio User Interface Definition ---
 with gr.Blocks(theme=gr.themes.Soft()) as demo:
@@ -233,9 +272,9 @@ with gr.Blocks(theme=gr.themes.Soft()) as demo:
             audio_input = gr.Audio(type="filepath", label="Upload Audio File")
             with gr.Accordion("Analysis Parameters", open=False):
                 threshold_slider = gr.Slider(10, 80, 40, step=1, label="Silence Threshold (dB)")
-                min_length_slider = gr.Slider(0.5, 30, 2, step=0.1, label="Min. Segment Length (s)")
+                min_length_slider = gr.Slider(0.5, 30, 1, step=0.1, label="Min. Segment Length (s)")
                 merge_length_slider = gr.Slider(1, 60, 15, step=1, label="Auto-Merge Threshold (s)")
-                min_silence_length_slider = gr.Slider(0.5, 60, 5, step=0.1, label="Merge Protection Length (s)")
+                min_silence_length_slider = gr.Slider(0.5, 60, 2, step=0.1, label="Merge Protection Length (s)")
             generate_button = gr.Button("Analyze Audio", variant="primary")
         
         with gr.TabItem("Start with CUE Text"):
@@ -251,19 +290,41 @@ with gr.Blocks(theme=gr.themes.Soft()) as demo:
 
         with gr.Row(visible=False) as merge_tools:
             merge_button = gr.Button("Merge Selected Tracks", variant="secondary", size="lg")
+        
+        # This group contains both Split and Edit tools, shown when one track is selected
+        with gr.Group(visible=False) as single_track_tools:
+            with gr.Accordion("Split Track", open=False):
+                split_slider_label = gr.Textbox(label="Current Split Time", interactive=False)
+                split_slider = gr.Slider(label="Drag to select split point")
+                split_button = gr.Button("Split Track at Selected Time", variant="secondary")
+            
+            # --- Edit Start Time ---
+            with gr.Accordion("Edit Start Time", open=True):
+                edit_time_input = gr.Textbox(label="New Start Time (MM:SS:FF)", placeholder="e.g., 01:23:45")
+                edit_time_button = gr.Button("Update Start Time", variant="secondary")
+
+    # --- Global Timeline Shift ---
+    with gr.Accordion("Global Edits", open=False, visible=False) as global_editing_group:
+        shift_amount_input = gr.Number(label="Timeline Shift Amount (seconds, +/-)", value=0)
+        shift_button = gr.Button("Apply Timeline Shift", variant="secondary")
 
-        with gr.Group(visible=False) as split_tools:
-            split_slider_label = gr.Textbox(label="Current Split Time", interactive=False)
-            split_slider = gr.Slider(label="Drag to select split point")
-            split_button = gr.Button("Split Track at Selected Time", variant="secondary")
 
     # --- Event Wiring ---
     
+    # Combined update for enabling editing groups
+    def show_editing_groups(times):
+        is_visible = bool(times)
+        return gr.update(visible=is_visible), gr.update(visible=is_visible)
+
     # Workflow 1: Audio analysis button now updates everything, including the editing tools.
     generate_button.click(
         fn=analyze_audio_to_cue,
         inputs=[audio_input, threshold_slider, min_length_slider, merge_length_slider, min_silence_length_slider],
-        outputs=[output_text, audio_filename_state, track_times_state, audio_duration_state, track_checkboxes, manual_editing_group]
+        outputs=[output_text, audio_filename_state, track_times_state, audio_duration_state, track_checkboxes]
+    ).then(
+        fn=show_editing_groups,
+        inputs=[track_times_state],
+        outputs=[manual_editing_group, global_editing_group]
     )
     
     # Workflow 2: Pasting text in the dedicated input box populates the main output and enables tools.
@@ -271,14 +332,18 @@ with gr.Blocks(theme=gr.themes.Soft()) as demo:
     cue_text_input_for_paste.change(
         fn=parse_cue_and_update_ui,
         inputs=[cue_text_input_for_paste],
-        outputs=[output_text, audio_filename_state, track_times_state, audio_duration_state, track_checkboxes, manual_editing_group]
+        outputs=[output_text, audio_filename_state, track_times_state, audio_duration_state, track_checkboxes]
+    ).then(
+        fn=show_editing_groups,
+        inputs=[track_times_state],
+        outputs=[manual_editing_group, global_editing_group]
     )
 
     # Dynamic UI controller for showing/hiding Merge/Split tools
     track_checkboxes.change(
         fn=update_editing_tools,
         inputs=[track_checkboxes, track_times_state, audio_duration_state],
-        outputs=[merge_tools, split_tools, split_slider, split_slider_label]
+        outputs=[merge_tools, single_track_tools, edit_time_input, split_slider, split_slider_label, edit_time_input]
     )
 
     # Live update for the split slider's time display
@@ -300,6 +365,19 @@ with gr.Blocks(theme=gr.themes.Soft()) as demo:
         inputs=[split_slider, track_times_state, audio_duration_state, audio_filename_state],
         outputs=[output_text, track_times_state, track_checkboxes]
     )
+    
+    # --- Action Buttons for New Features ---
+    shift_button.click(
+        fn=shift_timeline,
+        inputs=[shift_amount_input, track_times_state, audio_duration_state, audio_filename_state],
+        outputs=[output_text, track_times_state, track_checkboxes]
+    )
+    
+    edit_time_button.click(
+        fn=edit_track_start_time,
+        inputs=[track_checkboxes, edit_time_input, track_times_state, audio_duration_state, audio_filename_state],
+        outputs=[output_text, track_times_state, track_checkboxes]
+    )
 
 if __name__ == "__main__":
     demo.launch(inbrowser=True)