[FFmpeg-devel] [PATCH 2/4] avisynth: drop support of AviSynth 2.5

[Stephen Hutchinson]

On Tue, Mar 24, 2015 at 3:33 PM, Hendrik Leppkes <h.leppkes at gmail.com> wrote:
> On Tue, Mar 24, 2015 at 8:23 PM, Stephen Hutchinson <qyot27 at gmail.com> wrote:
>> If the user attempts to use AviSynth 2.5, an error message will
>> now tell them they need to upgrade.
>
> Whats the advantage in dropping support?
> Earlier versions seemed to work just fine against both 2.5 and 2.6.
>

If we want to make sure that we supply official and up-to-date
headers, then 2.5 support becomes harder to maintain.  The only
reason it currently supports 2.5* is the avisynth_c_25.h compat header,
which would have to be expanded with additional *_25 versions
of functions and cause more branching in the demuxer to
continue supporting it.

*more precisely, supports video under 2.5, because the
changes requiring the compat header were to video-related functions.

Also, the compat header was sourced from FFMS2's C plugin.
Now, since said header was originally committed to FFMS2 by the
same author that contributed C header work to earlier alphas of
AviSynth 2.6, I trust that the compat header is ISC licensed
rather than GPLv2 with linking exception was done without violating
the GPL.  But adding more functions to that header would be a lot trickier,
and ditching the compat header would resolve any what-ifs about
that situation (I'd rather even remove the 2.5 compat mode from FFMS2's
C plugin too, for that matter).


And while it doesn't pertain directly to the libavformat demuxer, users should
be strongly encouraged to upgrade to either 2.6 or better, AviSynth+,
since those versions are more stable than 2.5.  One of the main problems
was that users were scared off by classic AviSynth's 'alpha' tag on the 2.6
releases, even though the actual dev(s) stated the 'alpha' only referred to
2.6-specific features.  But with 2.6 RC1 having been out now for a
little over three months, the alpha argument can't hold sway anymore
(and AviSynth+ deliberately uses a different versioning scheme to
avoid this, and has since its inception in late 2013).