Does buffer data carries a sequence number while flowing through a pipeline?

[Nicolas Dufresne]

Le ven. 11 oct. 2019 06 h 55, jeyp4 <jaiforfriend at gmail.com> a écrit :

> Hello
> v4l2src -> timeoverlay -> vaapih265enc -> vaapidecode -> appsink
>
> Does data flowing through above(e.g.) pipeline carry any tag or any kind of
> sequence number?
>
> So that the final element(appsink) pad can match data tag with first
> element
> pad(v4l2src).
>
> My ultimate purpose is to provide a time-stamp to appsink data. Where the
> time-stamp can represent to image shot time as close as possible. I am
> flexible to use any time reference, e.g. ros::Time::now()
>

The timestamp is from v4l2src, which is in turn derived from whatever the
Linux/BSD kernel provided. It's a bit of a round trip, but here the
conversion flow.

v4l2src

Monotonic -> pipeline clock -> stream time

Pts = t + delta - base_time


So when you receive buffer in appasrc, to find back the monotonic time you
do the opposite.

T = pts - delta + base_time

Delta is the distance between pipeline clock now and time now. This is were
precision is lost, as there is no atomic way to retrieve this.



>
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