Add a "realtime=1" (alias "re=1") ffmpeg input option, modeled on the
existing "loop" option and equivalent to ffmpeg's -re flag. When set on a
file source, FfmpegCamera throttles packet delivery to the rate implied by
the stream timestamps instead of reading the file as fast as possible.
The option is parsed out of the ffmpeg Options string in OpenFfmpeg and
consumed so it is not passed to the demuxer or decoder. Capture() anchors
wall-clock time to the first delivered packet and sleeps before each
subsequent packet so it is not delivered ahead of schedule. Pacing uses dts
(monotonic in read order) with a pts fallback, runs after the existing
drop/jump filters, and re-anchors on backward jumps or gaps beyond a 10s cap
to avoid stalling on a discontinuity. Works alongside loop, whose
offset-adjusted timestamps stay monotonic across restarts.
The pacing decision is factored into a pure ComputeRealtimePace() function
and unit-tested in tests/zm_ffmpeg_camera.cpp (8 cases covering full/partial
interval waits, behind-schedule, on-schedule, backward jump, over-cap, and
the cap boundary).
Ported from the ai_server branch onto master's OpenFfmpeg structure.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
