The SPS NAL unit format is: [NAL header, profile_idc, constraint_flags, level_idc, ...]
The code was incorrectly reading from byte 0 (NAL header, typically 0x67)
instead of byte 1 (profile_idc).
This produced invalid codec strings like `avc1.676400` instead of valid
ones like `avc1.64001f`, causing Shaka Player on web to fail with error
4032 (unable to parse codec).
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>