[FFmpeg-devel] [PATCH 1/2] avcodec, avformat: deprecate anything related to side data merging

Michael Niedermayer michael at niedermayer.cc
Thu Mar 16 22:01:04 EET 2017

On Thu, Mar 16, 2017 at 05:20:51AM +0100, wm4 wrote:
> This patch deprecates anything that has to do with merging/splitting
> side data. Automatic side data merging (and splitting), as well as all
> API symbols involved in it, are removed completely.
> Two FF_API_ defines are dedicated to deprecating API symbols related to
> this: FF_API_MERGE_SD_API removes av_packet_split/merge_side_data in
> libavcodec, and FF_API_LAVF_KEEPSIDE_FLAG deprecates
> AVFMT_FLAG_KEEP_SIDE_DATA in libavformat.
> Since it was claimed that changing the default from merging side data to
> not doing it is an ABI change, there are two additional FF_API_ defines,
> which stop using the side data merging/splitting by default (and remove
> any code in avformat/avcodec doing this): FF_API_MERGE_SD in libavcodec,
> and FF_API_LAVF_MERGE_SD in libavformat.
> It is very much intended that FF_API_MERGE_SD and FF_API_LAVF_MERGE_SD
> are quickly defined to 0 in the next ABI bump, while the API symbols are
> retained for a longer time for the sake of compatibility.
> AVFMT_FLAG_KEEP_SIDE_DATA will (very much intentionally) do nothing for
> most of the time it will still be defined. Keep in mind that no code
> exists that actually tries to unset this flag for any reason, nor does
> such code need to exist. Code setting this flag explicitly will work as
> before. Thus it's ok for AVFMT_FLAG_KEEP_SIDE_DATA to do nothing once
> side data merging has been removed from libavformat.
> In order to avoid that anyone in the future does this incorrectly, here
> is a small guide how to update the internal code on bumps:
> - next ABI bump (probably soon):
>   - define FF_API_LAVF_MERGE_SD to 0, and remove all code covered by it
>   - define FF_API_MERGE_SD to 0, and remove all code covered by it
> - next API bump (typically two years in the future or so):
>   - define FF_API_LAVF_MERGE_SD to 0, and remove all code covered by it
>   - define FF_API_MERGE_SD_API to 0, and remove all code covered by it
> This forces anyone who actually wants packet side data to temporarily
> use deprecated API to get it all. If you ask me, this is batshit fucked
> up crazy, but it's how we roll. Making AVFMT_FLAG_KEEP_SIDE_DATA to be
> set by default was rejected as an ABI change, so I'm going all the way
> to get rid of this once and for all.
> ---

What is the advantage to deprecate the API ?

Applications which depend on the current default would need the code
provided by the API when the default changes

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Complexity theory is the science of finding the exact solution to an
approximation. Benchmarking OTOH is finding an approximation of the exact
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