OK, understood, I didn't initially get it. Thanks for the explanation, that
makes sense ! I promise I won't annoy you anymore, I apologize for the
inconvenience.
-----Original Message-----
From: live-devel <live-devel-boun...@us.live555.com> On Behalf Of Ross Finlayson
Sent: Monday, February 14, 2022 4:09 PM
To: LIVE555 Streaming Media - development & use <live-de...@us.live555.com>
Subject: Re: [Live-devel] compilation issue / vcpkg / windows
> On Feb 15, 2022, at 3:53 AM, g.jaegy <g.ja...@imagine3d.fr> wrote:
>
> So, you were right.
>
> Setting fPresentationTime using gettimeofday() solves the problem.
>
> Now, this however means the output frame time is not correlated to the time
> at which the original frame was captured (I'm capturing frames at 30Hz, but
> possibly the interval between two frames is not 100% constant, reason why I
> thought using the proper captured frame times would be a better idea to
> preserve smoothness).
>
> It also means different NALUs from a single frame have different time stamps,
> which I also thought was not correct.
>
> Do you know any source of information I could use to understand this two
> points ?
It’s OK to use frame counts etc. to set your “fPresentationTime” values, but
the *base value* - i.e., the value at the very start of your streaming - MUST
be the same as you’d get by calling “gettimeofday()”. I.e., it’s OK to do
something like this (pseudo-code):
if (this is the first frame that we’re sending) {
fPresentationTime = BaseTime = value from “gettimeofday()”;
} else {
fPresentationTime = BaseTime + frameCount/frameRate;
}
That’s what I meant when I said that your “fPresentationTime” values "must be
aligned with the values that you’d get by calling gettimeofday()”. Not that
each “fPresentationTime” must be computed by calling “gettimeofday()”, but that
“fPresentationTime” must start out with the same value as “gettimeofday()”, but
then can increase smoothly for each frame (and with the same value for multiple
NALUs within the same frame), based on the frame count and frame rate (assuming
that the frame rate remains constant).
This will be my (and I hope your :-) last posting on this thread.
Ross Finlayson
Live Networks, Inc.
http://www.live555.com/
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