[FFmpeg-devel] [PATCH] avcodec/version: Postpone FF_API_DEBUG_MV

Clément Bœsch u at pkh.me
Sun Oct 22 11:25:56 EEST 2017

On Sat, Oct 21, 2017 at 11:23:29PM -0300, James Almer wrote:
> >> The commit even states it should have removed "all traces of its use",
> >> but it looks like with the years more and more code was added to it,
> >> seeing the removal commit 8933ac2079644fb09916f1875c569103aefe84b1 in
> >> libav doesn't even feature the massive amount of code we have under this
> >> deprecation wrapper in mpegvideo.
> >> So basically, the functionality was deprecated, but then further
> >> developed to the point removing it is almost impossible.
> >>
> >> How the hell did this happen?
> > 
> > I dont know, maybe,
> > Libav deprecating and removing as much FFmpeg code as they can
> > FFmpeg continuing to work on the FFmpeg code
> No, i mean, why did a feature marked as deprecated keep getting
> development? Shouldn't the replacement have gotten it instead? And if a
> replacement was never planned, why wasn't the deprecation undone,
> instead of getting pushed further into the future indefinitely?

If I remember correctly (this needs double check), FFmpeg didn't continue
development of the frame debugging in MPEG after Libav deprecated it. On
the other hand, Libav did remove some code because it was broken by one of
their previous commit (see 37045e422; it was still working in FFmpeg at
that time unless I'm mistaken), so they had less code to deprecate in the

Around that time, I was trying to export the motion vectors and render
them in a filter instead (known as codecview), which would soon become the
first step at dropping that code from the MPEG codec. I was less
interested in the macroblock type debugging which is also part of the
visual MPEG debugging "toolkit", so I left it as an exercise for people
interested in it. It would be nice to have it in codecview, but I wasn't
motivated to do all the work.

So anyway, implementing this requires to export the information as side
data, and port the code from the MPEG codec to the codecview filter. I
don't think it's wise to drop the MPEG code until this is done since it's
useful in practice. Delaying (again) the drop is fine with me.

Clément B.
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