[FFmpeg-devel] [PATCH] avcodec: Add AVClass to AVCodecParameters

Nicolas George george at nsup.org
Thu May 19 12:08:25 CEST 2016

Le nonidi 29 floréal, an CCXXIV, Michael Niedermayer a écrit :
> there where and are accessor functions:

Yes, and they should have been the only way of avoiding ABI compatibility

Another point against AVClass: FFmpeg is mostly in C, C has static typing
and static typing is good.

That means that almost everywhere where AVClass is used, we know the type of
the structure we are handling, and therefore we know what AVClass we should
use. It could be an explicit parameter instead of an implicit parameter
hidden in the first field of the structure. The only case where we need it
is for private context for dynamic typing.

Therefore, I am rather strongly against adding AVClass fields to new
structures. I will not object in this instance if that fits the current
normal use of AVOption: if a patch series can make it so that dash-option on
the ffmpeg command-line reaches AVCodecParameters and does something useful,
then ok. But adding it just in case, no.

Note that I am easily convinced this is actually useful: if an option of
AVCodecParameters parameter could replace all the "video_size", "framerate",
etc., private options of rawvideodec, image2dec, etc., then adding the
fields is certainly a good idea. Still, there probably was a reason to make
these private options instead of accessing the codec fields directly like it
used to work. I do not remember what this reason was, and I have not yet
looked closely enough at AVCodecParameters to know if it can work that way.


  Nicolas George
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