Implement advanced export module with configurable metadata and live preview

[Copilot]

Separates export format selection from content configuration, allowing users to customize speaker and timestamp inclusion, placement, and formatting across all export formats.

Core Changes

ExportConfig dataclass - Configuration model for export options:

• Speaker: include toggle, placement (inline/separate)
• Timestamps: include toggle, placement (beginning/end/inline), type (start/range), format (HH:MM:SS variants)

Export methods - All methods now accept optional ExportConfig:

# Backward compatible - no config uses original behavior
editor.export_csv()  # → "00:00:01,000","00:00:03,500","Speaker A","text"

# With config - separate columns for metadata
config = ExportConfig(speaker_placement="separate", timestamp_format="HH:MM:SS.mmm")
editor.export_csv(config)  # → "00:00:01.000","00:00:03.500","Speaker A","text"

Helper methods:

• format_timestamp() - Converts between HH:MM:SS format variants
• generate_preview() - Renders first N segments with current config
• Format-specific preview generators for each export type

Export dialog - Modal UI replacing dropdown button:

• Left panel: format selector, speaker/timestamp configuration
• Right panel: live preview updating on any option change
• Dynamic option visibility (e.g., "separate" placement only for CSV/TSV/JSON)
• Smart enable/disable based on checkbox state

Technical Notes

CSV/TSV/JSON behavior: speaker_placement="separate" controls all metadata column structure. When "separate", timestamps and speakers go to distinct columns/fields; when "inline", metadata embeds in text field.

JSON export return type: Returns dict without config (backward compatibility), JSON string with config (consistency with other exporters).

Preview optimization: Processes only first 3 segments to maintain UI responsiveness.

Integration

Replaced multi-item export dropdown with single "Export..." button opening configuration dialog. All existing export functionality preserved.

Original prompt

Background

Implement the advanced export module as described in issue #37. The goal is to separate file format from content configuration, allowing users to customize what metadata is included in exports and how it is formatted.

Files to Modify

• utils/srt.py - Add export configuration classes and update export methods
• pages/srt.py - Add export dialog UI with configuration options

Requirements

1. Export Configuration Class

Add a new ExportConfig dataclass in utils/srt.py with the following options:

• include_speaker: bool - Toggle speaker information
• speaker_placement: str - "inline" or "separate" (for CSV/TSV/JSON)
• include_timestamps: bool - Toggle timestamps
• timestamp_placement: str - "beginning", "end", or "inline"
• timestamp_type: str - "start" or "range" (start-end)
• timestamp_format: str - Preset options: "HH:MM:SS", "HH:MM:SS,mmm", "HH:MM:SS.mmm"

2. Update Export Methods in SRTEditor class

Modify the following export methods to accept an optional ExportConfig parameter:

• export_txt() - Apply speaker and timestamp options
• export_rtf() - Apply speaker and timestamp options
• export_csv() - Apply speaker and timestamp options, support separate columns
• export_tsv() - Apply speaker and timestamp options, support separate columns
• export_json() - Apply speaker and timestamp options

Add helper methods:

• format_timestamp(timestamp: str, format_preset: str) -> str - Convert timestamp to specified format
• generate_preview(config: ExportConfig, format: str, num_segments: int = 3) -> str - Generate preview of export output

3. Export Dialog UI in pages/srt.py

Replace the simple dropdown export button with an "Export..." button that opens a dialog containing:

1. Format Selection - Radio buttons or select for: TXT, RTF, JSON, CSV, TSV (and SRT/VTT for srt data format)

2. Speaker Options Section

   • Checkbox: "Include speaker information"
   • Radio/Select (enabled when include_speaker is True): Speaker placement
     • "Inline prefix (e.g., 'Speaker A:')"
     • "Separate column/field" (only for CSV, TSV, JSON)

3. Timestamp Options Section

   • Checkbox: "Include timestamps"
   • Radio/Select (enabled when include_timestamps is True): Timestamp placement
     • "At beginning of each segment"
     • "At end of each segment"
     • "Inline with text"
   • Radio/Select: Timestamp type
     • "Start time only"
     • "Start–end range"
   • Select: Timestamp format preset
     • "HH:MM:SS"
     • "HH:MM:SS,mmm" (with comma)
     • "HH:MM:SS.mmm" (with dot)

4. Preview Panel

   • Show a live preview of the first 2-3 segments
   • Update preview immediately when any option changes
   • Display in a styled code/text block

5. Action Buttons

   • "Cancel" - Close dialog
   • "Export" - Execute export with selected options

4. UI/UX Considerations

• Disable speaker placement options when "Include speaker information" is unchecked
• Disable timestamp options when "Include timestamps" is unchecked
• Show/hide "Separate column/field" option based on selected format
• Preview should reflect exact export output format
• Use consistent styling with existing UI (NiceGUI components, existing CSS classes)

Reference Code Locations

• Current export methods: utils/srt.py lines 332-433
• Current export UI: pages/srt.py lines 131-171
• Existing dialog pattern: utils/srt.py lines 1148-1183 (validate_captions dialog)

This pull request was created from Copilot chat.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.