Fix visual frame evidence to show actual video frame indices

[codegen-sh]

Summary

Fixes CG-19004: Updates the visual frame evidence display to show actual video frame indices instead of just the extraction indices.

Problem

Previously, the visual frame evidence showed "Frame 2" and "Frame 3" which were just the sequential extraction indices (frame_002.png, frame_003.png). These numbers didn't represent the actual position within the video, making the evidence confusing and less meaningful.

Solution

• Store video frame rate: Extract and store the video's fps during metadata analysis
• Calculate actual video frame indices: Use timestamp × fps to determine real video frame numbers
• Enhanced discontinuity analysis: Track both extraction indices and actual video frame positions
• Improved visual evidence: Display actual video frame numbers with proper timestamps
• Better formatting: Add helper methods for timestamp and file size formatting
• Template updates: Clarify that these are "Video Frame" indices in the HTML output

Changes Made

Core Logic (epstein_video_analyzer.py)

• Added self.fps instance variable to store video frame rate
• Enhanced analyze_frame_discontinuities() to calculate actual video frame indices
• Added _format_timestamp() and _format_file_size() helper methods
• Updated visual evidence generation to use real frame indices and timestamps
• Store actual file sizes from analysis instead of hardcoded values

Template (templates/report.html)

• Updated display text from "Frame X" to "Video Frame X" for clarity

Testing

• Added test_frame_indices.py to verify frame calculation logic
• All timestamp and file size formatting tests pass
• Frame calculations are accurate within expected rounding tolerance

Example Output

Before:

Frame 2 (6h36m00s): 2,155,188 bytes
Frame 3 (6h36m01s): 2,263,396 bytes

After:

Video Frame 712057 (6h35m59s): 2,155,188 bytes  
Video Frame 712087 (6h36m00s): 2,263,396 bytes

Now the frame numbers represent the actual position within the video (at ~29.97 fps), making the forensic evidence much more meaningful and accurate.

Testing

Run the test script to verify the calculations:

python3 test_frame_indices.py

The changes maintain backward compatibility while providing more accurate and meaningful frame evidence for forensic analysis.

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