[FFmpeg-devel] [PATCH 2/5] fftools/ffmpeg: move parsing of -stats_* specifiers to lavu/parseutils

[Anton Khirnov]

Quoting Thilo Borgmann via ffmpeg-devel (2023-12-13 13:50:09)
> Am 13.12.23 um 13:39 schrieb Anton Khirnov:
> > Quoting Thilo Borgmann via ffmpeg-devel (2023-12-13 13:15:27)
> >> Am 13.12.23 um 13:08 schrieb Anton Khirnov:
> >>> Quoting Thilo Borgmann via ffmpeg-devel (2023-12-13 13:05:35)
> >>>> Am 13.12.23 um 13:00 schrieb Anton Khirnov:
> >>>>> Quoting Thilo Borgmann via ffmpeg-devel (2023-12-11 16:07:22)
> >>>>>> ---
> >>>>>>     fftools/ffmpeg.h          |  31 +------
> >>>>>>     fftools/ffmpeg_enc.c      |   3 +-
> >>>>>>     fftools/ffmpeg_mux_init.c | 152 +++-----------------------------
> >>>>>>     libavutil/parseutils.c    | 176 ++++++++++++++++++++++++++++++++++++++
> >>>>>>     libavutil/parseutils.h    | 102 ++++++++++++++++++++++
> >>>>>>     libavutil/version.h       |   2 +-
> >>>>>>     6 files changed, 296 insertions(+), 170 deletions(-)
> >>>>>
> >>>>> Absolutely not.
> >>>>>
> >>>>> This is application code and does not belong in the libraries.
> >>>>
> >>>> How else do we not have a redundant copy of all that and make sure that -stats_* options and the filter understand the same {..} directives?
> >>>
> >>> Why does that filter need to understand the same directives? No other
> >>> filter does.
> >>
> >> Because it is meant to use the file(s) the -stats_* option writes out. The most convenient and most error resilient way is to use the very same format string for -stats_* option as well as for the filter.
> >>
> >> Otherwise it could be a 'usual' scanf-format, but then the user has to translate it from one format into the other - without making mistakes.
> >> But that would also mean to update the filter (if someone realizes it) if the option ever changes.
> > 
> > Why does it need a dynamic format at all? Just postulate a fixed format
> > for its input like every other filter and none of this complexity is
> > needed.
> 
> That would unnecessarily limit the user of the -stats_* option to a
> specific format if the user also wants to use this filter later.
> Either sacrificing the other info the user wanted to process from the
> file created or having to run the same command (with distinct format
> strings for the -stats_* option) twice. Or do the conversion from his
> extensive format into the fixed format manually - without errors.

It is bad practice to design library features around the needs and
limitations of a single specific caller.

Many of the directives supported by -stats* make sense only in the
context of the ffmpeg CLI, and we may want to add many more in the
future. We definitely do not want to hardcode them into libavutil public
API.

If the problem is limiting ffmpeg CLI users to a specific stats format,
then you could extend these options to allow writing multiple stats
files with different formats.

-- 
Anton Khirnov