[FFmpeg-devel] [PATCH 3/3] lavc: remove Libav ABI compat hacks

Nicolas George george at nsup.org
Sat Sep 5 20:58:12 CEST 2015

Le nonidi 19 fructidor, an CCXXIII, James Almer a écrit :
> Without this option, the AVPixelFormat enum values in libavutil/pixfmt.h
> don't match between projects. It's absolutely needed for abi
> compatibility, so knowing if anyone used it is important because it will
> show if said compatibility was ever used/needed or not.

I believe that Ronald, Paul and you miss the point that I am making. I will
re-state the problem clearly, please read carefully, and if you do not agree
with a particular point, please answer with precision.

Until now, it has been a project policy to ensure API and ABI compatibility
with the fork as much as possible.

One of the constraints caused by that policy is this: codec-id values added
in FFmpeg must not conflict with codec-id values added later by libav.

This is done by using 4cc values, which is not an issue at all.

Along the way, a few cases were missed. It causes minor ABI
incompatibilities, negligible in real situations. See "as much as possible"
in the policy statement above.

Since there is a major bump going on, there is an occasion to fix the
incompatibilities. Very good.

But fixing the present incompatibilities does not prevent future

To continue maintaining compatibility, the 4cc values must stay.

The current patch removes the 4cc values, replacing them with normal
enumerated order, that will conflict with the first addition in libav.

In short: with the bump, we can clean-up and restart with perfect ABI
compatibility, now and in the future. This patch breaks it. Do you support


  Nicolas George
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