Port the C++ srs_protocol_rtmp_stack.cpp fix (#4356) to the Go proxy's RTMP parser in internal/rtmp.
For chunk fmt=1/2 the extended timestamp encodes a timestamp delta, not an absolute timestamp. The parser previously assigned the extended value to the message timestamp unconditionally, so once a delta reached 0xffffff the DTS was miscomputed, and since audio and video deltas differ this could cause A/V desync.
Changes:
- Split chunkStream's single ext-ts bool into hasExtendedTimestamp (presence) plus a raw extendedTimestamp uint32, mirroring the C++ has_extended_timestamp_ / extended_timestamp_ fields.
- Compute the message timestamp once: extended value when present, else the 3-byte header delta; assign it as absolute for fmt=0 and accumulate it as a delta for fmt=1/2 (and a fmt=3 first chunk).
- Resolve the 'detect the extended timestamp' TODO: peek the 4 bytes and leave them as payload when a librtmp/ffmpeg-style sender omits the ext-ts on a Type-3 chunk (Go equivalent of the C++ skip(-4)).
- Add unit tests for the fmt=1 delta-crossing-0xffffff case and the Type-3 omitted-ext-ts case.
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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