[FFmpeg-devel] [PATCH] extractplanes filter

Nicolas George nicolas.george at normalesup.org
Fri May 3 12:18:48 CEST 2013

Le tridi 13 floréal, an CCXXI, Paul B Mahol a écrit :
> I wonder how format renegotiation works. I would like to pick 16bit gray
> with right endianess depending on input format - if its 16 bit at all
> otherwise just pick 8bit one.

That would be useful in this situation indeed.

The basic principle is this: query_formats() sets the formats it can, and if
it could not set everything it returns EAGAIN, and will be called again
later, hopefully when more information is available.

In this situation, I believe the correct flow is this:

    if input formats are not set
        set input formats to all 8 and 16 bits formats
    if input formats still contains several bit depths
        return AVERROR(EAGAIN)
        set output formats to the corresponding gray format

> I can't find where its explained how to do that.

There is a small paragraph in doc/filter_design.txt, it could be expanded,
possibly with an example.


  Nicolas George
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