fix: improve media format detection with proper ftyp-based MP4 detection

[0xsatoshi99]

Summary

Fixes incorrect MP4 format detection in C2PA verification by using proper ftyp-based detection instead of hardcoded box sizes. Also adds comprehensive support for additional media formats.

Problem

The previous implementation detected MP4 files by checking for specific ftyp box sizes:

elif data[:4] == b'\x00\x00\x00\x1c' or data[:4] == b'\x00\x00\x00\x20':
    return ".mp4"

This only catches MP4 files with ftyp box sizes of 28 or 32 bytes. Many valid MP4 files have different box sizes and would incorrectly return .bin, causing C2PA verification to fail.

Solution

Check for ftyp signature at offset 4 (the standard location per ISO base media file format):

if len(data) >= 8 and data[4:8] == b'ftyp':
    return ".mp4"

Changes

Bug Fix

• MP4 detection: Use ftyp-based detection instead of hardcoded box sizes
• JPEG detection: Improved with 3-byte signature (FF D8 FF)
• Length checks: Added bounds checking to prevent index errors on short data

New Format Support

Category	Formats Added
Images	GIF, BMP, TIFF, HEIC/HEIF, AVIF
Video	MOV, 3GP, AVI (+ improved MP4)
Audio	MP3, WAV, FLAC, OGG, M4A

Testing

Manual verification with sample files of each format type.

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Contribution by Gittensor, learn more at https://gittensor.io/

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Note

Improves media format detection for C2PA verification using ftyp-based parsing and adds broad image, video, and audio format support with safer bounds checks.

• Verification (gas/verification/c2pa_verification.py)
  • Format detection (_detect_format):
    • Switch to ftyp-based parsing for ISO-BMFF formats (MP4/M4A/MOV/3GP/HEIC/AVIF) with brand-specific mapping.
    • Add detection for additional formats: GIF, BMP, TIFF, AVI, WebM/MKV, MP3, WAV, FLAC, OGG.
    • Improve JPEG detection to 3-byte signature and add length/bounds checks.
    • Expand docstring and return .bin for unknowns.

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[0xsatoshi99]

@dylanuys Can you plz check this PR and give me your feedback? Thanks.