Create README.md of UI/Description

Author: woshimajintao

annotation_tool/ui/description/README.md

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+# 📝 UI: Description Mode
+
+This directory contains the user interface components specifically designed for the **Description (Global Captioning)** mode.
+
+In this mode, the focus is on providing a holistic text description for video content. The interface is divided into a **Composite Media Player** (Center) and a **Text Event Editor** (Right).
+
+## 📂 Directory Structure
+
+```text
+ui/description/
+├── event_editor/
+│   ├── __init__.py           
+│   └── editor.py             # Right Panel: Text Input & Action Buttons
+│
+└── media_player/
+    ├── __init__.py           # Center Panel: Composite Widget (Combines Preview + Controls)
+    ├── player_panel.py       # Internal: Video Surface, Slider, & Time Label
+    └── controls.py           # Internal: Navigation Toolbar (Play/Pause, Next/Prev)
+
+```
+
+---
+
+## 🧩 Components
+
+### 1. Media Player (Center Panel)
+
+The Center Panel is a **Composite Widget** defined in `media_player/__init__.py`. It orchestrates the video display and the navigation controls into a single layout.
+
+#### A. Main Wrapper (`media_player/__init__.py`)
+
+* **Class:** `DescriptionMediaPlayer`
+* **Purpose:** Acts as the main container for the center of the screen.
+* **Layout:** A `QVBoxLayout` that stacks:
+1. `DescriptionMediaPreview` (The Video & Slider) - *Stretches to fill space*.
+2. `DescriptionNavToolbar` (The Buttons) - *Fixed height at bottom*.
+
+
+* **API:** It exposes crucial UI elements (`player`, `play_btn`, `next_clip`, etc.) so the Controller can easily connect signals without digging into child widgets.
+
+#### B. Visual Preview (`media_player/player_panel.py`)
+
+* **Class:** `DescriptionMediaPreview`
+* **Purpose:** Renders the video and handles timeline interaction.
+* **Key Features:**
+* **Shared Surface:** Uses the common `VideoSurface` for consistent rendering.
+* **Infinite Loop:** Sets `QMediaPlayer.Loops.Infinite` to allow repeated viewing while typing.
+* **Clickable Slider:** A custom `QSlider` allowing absolute positioning on click.
+* **Time Label:** Displays current position vs. total duration.
+
+
+
+#### C. Navigation Toolbar (`media_player/controls.py`)
+
+* **Class:** `DescriptionNavToolbar`
+* **Purpose:** Provides playback and navigation controls.
+* **Buttons:**
+* **Action Navigation:** `<< Prev Action` / `Next Action >>` (Navigates logical events).
+* **Clip Navigation:** `< Prev Clip` / `Next Clip >` (Navigates physical video files).
+* **Playback:** `Play / Pause` toggle.
+
+
+
+---
+
+### 2. Event Editor (Right Panel)
+
+Located in `event_editor/editor.py`.
+
+* **Class:** `DescriptionEventEditor`
+* **Purpose:** The input interface for the captioning task.
+* **Components:**
+* **Text Area:** A `QTextEdit` for multi-line description entry.
+* **History:** `Undo` and `Redo` buttons (linked to the generic history manager).
+* **Actions:**
+* **Clear:** Resets the text field.
+* **Confirm:** Submits the text as the description for the current clip.
+
+
+
+
+
+---
+
+## 🎨 Component Composition
+
+The Description UI is assembled hierarchically:
+
+```mermaid
+graph TD
+    subgraph "Center Panel (DescriptionMediaPlayer)"
+        Container[media_player/__init__.py]
+        
+        Preview[player_panel.py]
+        Controls[controls.py]
+        
+        Container --> Preview
+        Container --> Controls
+        
+        subgraph "Preview Components"
+            Video[VideoSurface]
+            Slider[ClickableSlider]
+        end
+        
+        Preview --> Video
+        Preview --> Slider
+    end
+
+    subgraph "Right Panel (DescriptionEventEditor)"
+        Editor[event_editor/editor.py]
+        Input[QTextEdit]
+        Confirm[Confirm Button]
+        
+        Editor --> Input
+        Editor --> Confirm
+    end
+
+```