Re: [FFmpeg-devel] [PATCH v2 1/1] avfilter/vf_vpp_qsv: apply 3D LUT from file.

[Chen Yufei <cyfdecyf@gmail.com>]

On Tue, Jan 30, 2024 at 1:07 AM Anton Khirnov <anton@khirnov.net> wrote:
>
> Quoting Chen Yufei (2024-01-29 04:01:51)
> > On Sun, Jan 28, 2024 at 10:10 PM Anton Khirnov <anton@khirnov.net> wrote:
> > >
> > > Quoting Zhao Zhili (2024-01-28 14:51:58)
> > > >
> > > >
> > > > > On Jan 28, 2024, at 18:31, Anton Khirnov <anton@khirnov.net> wrote:
> > > > >
> > > > > Quoting Chen Yufei (2024-01-25 17:16:46)
> > > > >> On Wed, Jan 24, 2024 at 7:39 PM Anton Khirnov <anton@khirnov.net> wrote:
> > > > >>>
> > > > >>> Quoting Chen Yufei (2024-01-20 16:14:29)
> > > > >>>> Usage: "vpp_qsv=lut3d_file=<path to file>"
> > > > >>>
> > > > >>> Passing file paths to a filter and having the filter load the file is
> > > > >>> not recommended, it is generally preferable to have an
> > > > >>> AV_OPT_TYPE_BINARY option, with IO performed by the caller.
> >
> > "is not recommended, it is generally preferable"
> > I take this as using `AV_OPT_TYPE_BINARY` is not a MUST.
> >
> > I'm not an English native speaker, correct me If I'm wrong.
> >
> > > > >>>
> > > > >>> E.g. in ffmpeg CLI you can do
> > > > >>> -filter vpp_qsv=/lut3d=<file>
> > > > >>> to load the option value from a file.
> > > > >>
> > > > >> I searched for code using `AV_OPT_TYPE_BINARY`.
> > > > >> `vf_libplacebo.c` gives me a good example.
> > > > >>
> > > > >> The LUT parsing code is took from `libavfilter/vf_lut3d.c`.
> > > > >> It's mainly text processing which calls functions on `FILE*`.
> > > > >> Using `AV_OPT_TYPE_BINARY` would require many changes in LUT paring
> > > > >> code, and also need to change the command line option of `vf_lut3d`.
> > > > >> So I'd keep the lut file option as is.
> > > > >
> > > > > Your patch is rejected then.
> >
> > Now I understand using `AV_OPT_TYPE_BINARY` is a must.
>
> Okay, sorry for being unclear. When I say 'recommended', it means it
> must be done this way unless there is a strong technical reason to do it
> otherwise. But then please provide a detailed explanation, not
> something vague like "didn't seem appropriate".

After taking more time looking into how to use `AV_OPT_TYPE_BINARY`,
I'll give more details.

1. For LUT file parsing, I'm not writing new code, it's taken from
existing vf_lut3d.c.
    I avoid making unnecessary modifications to avoid breaking things.

2. The original code relies on file name to detect LUT file type, uses
`fgets` and the like.
    From my understanding, `AV_OPT_TYPE_BINARY` does not give the file
name to the calling filter.
    If we use `AV_OPT_TYPE_BINARY`, then how to do file type detection?
    Adding other cmdline option would require changing vf_lut3d's
cmdline option.

3. I tried to find basic text processing utils in FFmpeg to avoid
writing ad-hoc text processing code in lut3d.c
    I've found `FFTextReader` in libavformat/subtitles.h, but I don't
think I should use it in filter code.
    I'm not sure if it's OK to follow the code in `FFTextReader` and
duplicate read line logic in lut3d.c.

Besides, there's `BINARY` in the name of `AV_OPT_TYPE_BINARY`, but
what I'm specifying here is text file.
This is not a big problem, but seem like an option name like
`AV_OPT_TYPE_TEXT` can express the usage of the option more clear in
code.

>
> --
> Anton Khirnov

-- 
Best regards,
Chen Yufei
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