InputStreamHealth.realtimeDeltaMs property

wallclock now − the last frame’s media timestamp (ms), measured at the input.

This is a RELATIVE quantity — do NOT read its absolute sign or magnitude as "seconds behind realtime". It carries a source-dependent offset that has nothing to do with the receiver: a startup lead (a publisher typically dumps its first GOP the instant it connects, stamping media time ahead of now) plus accumulated source-vs-receiver clock skew (a source running even ~1% fast makes this drift steadily more negative). It is commonly negative on a perfectly healthy input.

Use the TREND, not the value: realtimeDeltaSlopeMsPerS is the drift signal and lastMediaAgeMs is the stall signal.

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