On 2021-05-02 15:20, Bouke wrote:
On 2 May 2021, at 11:02, Marton Balint <[email protected]> wrote:
On Sun, 2 May 2021, Bouke wrote:
From the manual:
'timestamp_align
Capture start time alignment in seconds. If set to nonzero, input frames are
dropped till the system timestamp aligns with configured value
Ok, when I put -timestamp_align in my command, it does wait ‘a bit’ before
starting capture.
That’s what I’m after, but i have no clue how long it waits. It’s not a ‘wait X
seconds’ for sure.
It waits until UTC modulo timestamp_align becomes 0. So for 60 it waits until a
full minute boundary is reached.
Ok, but what is ' UTC modulo’ ?
If i enter 0, it starts capturing immediately, higher values do give ‘a’ delay,
but it’s not predictable at all.
(It’s off by a random value, up to 30% difference from what I expect…)
The actual check is to take the modulus of the system time with respect
to timestamp_align.
If this modulus is less than one frame duration (inverse of framerate),
then it starts capture.
So let's say timestamp_align is 0.5s and framerate is 25, so frame
duration is 40ms.
If system time is 1000.40s, then modulus is 400ms which is greater than
40ms, so capture doesn't start.
If it's 1000.53s, then modulus is 30ms, which is less than 40ms so
capture is initiated.
Regards,
Gyan
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