[FFmpeg-user] how to got microsecond for the start TimeStamp of FFmpeg export .avi ?

[Zoom.Quiet]

background:
in win10, ew usage FFmpeg capture web cam. as .avi;
for base OpenCV analyze pupil/..etc. info.

problem:
we know FFmpeg load and work need time,
so means from call FFmpeg to real write .avi into disk , had to wait
random time;
but the pupil video must very accurate match with other camera frame events;
so we need know the timestamp as microsecond for the accurate start
time with FFmpeg recording.
because other camera base Python with OpenCV capture and export as frame image,
with microsecond timestamp as file name, such as:
1543892896.5286150.jpg
...

if we know the accurate start timestamp for .avi;
so we can base fps count every frame's microsecond timestamp, to match
other frame events

BUT:
FFmpeg not record frame timestamp into .avi or others video file,
and the .avi file's attribute only include:
create time; update time;
them all not the FFmpeg accurate start reording time.

so any suggest?

thanx for all.

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