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

[Paul B Mahol]

On Fri, Sep 22, 2023 at 2:39 PM Clément Péron <peron.clem at gmail.com> wrote:

> Hi Paul,
>
> On Fri, 22 Sept 2023 at 13:41, Paul B Mahol <onemda at gmail.com> wrote:
> >
> > On Fri, Sep 22, 2023 at 12:06 PM Clément Péron <peron.clem at gmail.com>
> wrote:
> >
> > > Hi Paul
> > >
> > > On Fri, 22 Sept 2023 at 11:27, Paul B Mahol <onemda at gmail.com> wrote:
> > > >
> > > > On Fri, Sep 22, 2023 at 10:38 AM Clément Péron <peron.clem at gmail.com
> >
> > > wrote:
> > > >
> > > > > Hi Andreas,
> > > > >
> > > > > On Fri, 22 Sept 2023 at 09:58, Andreas Rheinhardt
> > > > > <andreas.rheinhardt at outlook.com> wrote:
> > > > > >
> > > > > > Clément Péron:
> > > > > > > Hi Michael, Andreas,
> > > > > > >
> > > > > > > On Thu, 21 Sept 2023 at 22:50, Andreas Rheinhardt
> > > > > > > <andreas.rheinhardt at 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 at 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.
>

FFmpeg usually supports files found in wild, and not inventing own formats
unless there is very good reason for it.


>
> 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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