[FFmpeg-user] "documented implicitly" [was: Re: Why is format=rgb24 required after maskedmerge?]

Paul B Mahol onemda at gmail.com
Wed Aug 19 20:53:30 EEST 2020

On 8/19/20, Jim DeLaHunt <list+ffmpeg-user at jdlh.com> wrote:
> On 2020-08-19 07:34, Paul B Mahol wrote:
>> You are deeply confused about our filters.
>> Any filter can change pixel formats to one that they accepts thus gbrp
>> is picked instead of packed rgb, this is already documented
>> implicitly.
> Wow, "documented implicitly". This is such a classic FFmpeg project
> statement. The role of documentation is to explain, explicitly, at a
> suitable level of detail. What does "documented implicitly" even mean?
> I think this thread points out is that FFmpeg documentation is
> inadequate. It is hard to prove a negative, but I suspect that the term
> "pixel format" is not actually defined in the FFmpeg documentation. I
> suspect that the statement, "Any filter can change pixel formats" is not
> stated either. Certainly the maskedmerge filter documentation[1] doesn't
> mention pixel formats at all, much less say what pixel formats the
> filter sets for its output.
> I have attempted to improve the documentation, to make it explain
> explicitly instead of fail to document. I encountered a great deal of
> resistance to those patches, because they make the documentation more
> explicit, because they have more words, and because documentation has so
> little value in this project relative to executable code.
> And yet "You are deeply confused about our filters". In other words, the
> documentation has failed to explain to you what FFmpeg does, the project
> has failed to write or welcome improved documentation, you do not
> understand how FFmpeg works — and somehow this is your fault.


mention it explicitly:

Libavfilter will automatically insert scale filters where format
conversion is required. It is possible to specify swscale flags for
those automatically inserted scalers by prepending sws_flags=flags; to
the filtergraph description.

> [1] http://ffmpeg.org/ffmpeg-all.html#maskedmerge
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