Re: [FFmpeg-devel] [RFC PATCH 3/3] HACK: avformat: rawenc: allow to output a raw PRFT

["Clément Péron" <peron.clem@gmail.com>]

Hi Paul,

On Fri, 22 Sept 2023 at 13:41, Paul B Mahol <onemda@gmail.com> wrote:
>
> On Fri, Sep 22, 2023 at 12:06 PM Clément Péron <peron.clem@gmail.com> wrote:
>
> > Hi Paul
> >
> > On Fri, 22 Sept 2023 at 11:27, Paul B Mahol <onemda@gmail.com> wrote:
> > >
> > > On Fri, Sep 22, 2023 at 10:38 AM Clément Péron <peron.clem@gmail.com>
> > wrote:
> > >
> > > > Hi Andreas,
> > > >
> > > > On Fri, 22 Sept 2023 at 09:58, Andreas Rheinhardt
> > > > <andreas.rheinhardt@outlook.com> wrote:
> > > > >
> > > > > Clément Péron:
> > > > > > Hi Michael, Andreas,
> > > > > >
> > > > > > On Thu, 21 Sept 2023 at 22:50, Andreas Rheinhardt
> > > > > > <andreas.rheinhardt@outlook.com> wrote:
> > > > > >>
> > > > > >> Michael Niedermayer:
> > > > > >>> On Thu, Sep 21, 2023 at 02:17:00PM +0200, Clément Péron wrote:
> > > > > >>>> Output the producer reference time to a dirty raw output.
> > > > > >>>>
> > > > > >>>> Signed-off-by: Clément Péron <peron.clem@gmail.com>
> > > > > >>>> ---
> > > > > >>>>  libavformat/rawenc.c | 122
> > > > +++++++++++++++++++++++++++++++++++++++++++
> > > > > >>>>  1 file changed, 122 insertions(+)
> > > > > >>>
> > > > > >>> this breaks fate-filter-volume and others
> > > > > >>> (Segmentation fault)
> > > > > >>>
> > > > > >>> I can rerun it with debug symbols and provide peoper gdb output
> > > > > >>> but i suspect given this has "HACK" in the title you are aware of
> > > > this
> > > > > >
> > > > > > The "HACK" tag meaning was not supposed to be: "it's ok if it
> > > > > > segfaults", but more to trigger a discussion is it possible to
> > > > > > properly support an output timestamp in the raw video demux, and if
> > > > > > yes how to do it :)
> > > > >
> > > > > If you need a timestamp for raw video, then use a proper container
> > and
> > > > > not raw video. In fact, this patch basically creates new formats
> > > > > different from all the raw formats.
> > > >
> > > > Yes I agree, but I do not want to add too much overhead nor
> > > > computation processing or memory copy to my pipeline just to mux and
> > > > demux between ffmpeg and my python script.
> > > >
> > > > The idea is to have a very light structure to easily pipe it.
> > > >
> > > > I'm not familiar with audio/video container but it seems to me that
> > > > parsing containers are not very light no?
> > > >
> > > >
> > > Containers range from almost no processing like .y4m to complex monsters
> > > like .mxf
> >
> > .y4m doesn't contain a timestamp either, and I don't want to use a
> > complex container :),
> >
>
> I doubt storing clock time in container for each frame is correct approach.
> Is this variable frame rate video?

Why would it not? The python takes as an input a list of frames.
It then runs an inference model on it and could discard some frames if needed.
Taking the absolute timestamp of each frame avoids relying on a
supposed frame rate (based on a free running clock) that is not
guaranteed.
Also the result gives inference results which are properly timestamped
with the correct data acquisition time and I can easily resynchronize
with other sensor acquisition.

>
> One can always add another, trivial container with just one field having
> whatever you want and with optional magic string in header.

Yes, if this is acceptable by FFMpeg community I could propose a
trivial container where the format is user defined.
Else I can keep this dirty patch downstream, but I'm not a big fan.

Regards,

>
> Or can try/explore NUT container in FFmpeg.
>
>
> >
> > >
> > > This patch is hack and approach/solution it tries is flawed.
> >
> > 100% agree with you that's why I prefix the patch with "HACK:",
> >
> > Regards,
> > Clement
> >
> >
> > >
> > >
> > > > Thanks,
> > > > Clement
> > > >
> > > >
> > > > >
> > > > > - Andreas
> > > > >
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