Description

Fixes WebVTT caption parsing when X-TIMESTAMP-MAP contains large MPEGTS values (e.g., 183600). Previously, the parser would throw "Malformed WebVTT signature" errors and fail to load captions.

Problem

When WebVTT files contain X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:183600, the parser rejects them as malformed, preventing caption display. This is common with videos processed by Elemental Media Engine and other video processing tools.

Steps to Reproduce

1. Load HLS stream with WebVTT captions containing large MPEGTS values
2. Enable captions
3. Observe "Malformed WebVTT signature" error in console and missing captions

Solution

• Modified WebVTT parser to handle larger MPEGTS values gracefully
• Added normalization for extremely large timestamp values while maintaining standards compliance
• Maintains backward compatibility with standard MPEGTS values

Testing

• ✅ Verified fix with problematic stream: https://course-dev.heysimon.com/asset/draft/7baab12c-3cbb-45f7-9047-f4635f6d8b0f/a9c44c80-fd57-4158-a3da-9c353b2cde7c/5d50b519-6335-4ed9-8284-3e46834aff43.m3u8
• ✅ All existing tests pass
• ✅ Added new test cases for large MPEGTS values
• ✅ No regressions in standard WebVTT parsing