[FFmpeg-devel] [PATCH] libavcodec/dnxhdenc: remove setting the codec_tag

[Michael Niedermayer]

On Fri, Aug 05, 2016 at 12:58:10PM +0200, Paul B Mahol wrote:
> On 8/5/16, Michael Niedermayer <michael at niedermayer.cc> wrote:
> > On Wed, Aug 03, 2016 at 02:31:04PM -0700, Mark Reid wrote:
> >> setting the codec_tag no longer needed by movenc
> >> it uses the dnxhr profile instead
> >> ---
> >>  libavcodec/dnxhdenc.c | 3 ---
> >>  1 file changed, 3 deletions(-)
> >>
> >> diff --git a/libavcodec/dnxhdenc.c b/libavcodec/dnxhdenc.c
> >> index b0ee8a2..cbf4cd5 100644
> >> --- a/libavcodec/dnxhdenc.c
> >> +++ b/libavcodec/dnxhdenc.c
> >> @@ -341,9 +341,6 @@ static av_cold int dnxhd_encode_init(AVCodecContext
> >> *avctx)
> >>      }
> >>      av_log(avctx, AV_LOG_DEBUG, "cid %d\n", ctx->cid);
> >>
> >> -    if (ctx->cid >= 1270 && ctx->cid <= 1274)
> >> -        avctx->codec_tag = MKTAG('A','V','d','h');
> >
> > does this not break older libavformat ?
> > newer libavcodec could be used with older libavformat
> 
> Are you serious? That kind of scenario is bad idea and it never worked
> and was never tested.

its tested by the users of binary packages in linux distros
debian and ubuntu being examples

each lib has major, minor and micro versions

    MAJOR version when you make incompatible API changes,
    MINOR version when you add functionality in a backwards-compatible manner, and
    PATCH version when you make backwards-compatible bug fixes.
(taken from http://semver.org/)

so if minor is bumped in libavcodec then it has a new feature and
libavformat at that point and later might need that feature and
thus there will be a matching dependancy libavformat->libavcodec >= x.y

but if libavformat bumps minor, libavcodec does not depend on
libavcodec thus there wont be a dependancy.

any lib with larger minor version must work as a drop in for older
versions of same major version

you can also see this in the actual dependancies on ubuntu for example:

apt-cache show libavformat-ffmpeg56 libavcodec-ffmpeg56 | grep Depends

Depends: libavcodec-ffmpeg56 (>= 7:2.7) | libavcodec-ffmpeg-extra56 (>= 7:2.7), libavutil-ffmpeg54 (>= 7:2.8), libbluray1 (>= 1:0.2.2), libbz2-1.0, libc6 (>= 2.14), libgme0 (>= 0.5.5), libgnutls30 (>= 3.4.2), libmodplug1 (>= 1:0.8.8.5), librtmp1 (>= 2.3), libssh-gcrypt-4 (>= 0.4.2), zlib1g (>= 1:1.2.0.2)

Depends: libavutil-ffmpeg54 (>= 7:2.6), libc6 (>= 2.14), libcrystalhd3
(>= 1:0.0~git20110715.fdd2f19), libgsm1 (>= 1.0.13), liblzma5 (>= 5.1.1alpha+20120614), libmp3lame0, libopenjpeg5 (>= 1.3+dfsg), libopus0 (>= 1.1), libschroedinger-1.0-0 (>= 1.0.0), libshine3 (>= 3.1.0), libsnappy1v5, libspeex1 (>= 1.2~beta3-1), libswresample-ffmpeg1 (>= 7:2.4), libtheora0 (>= 1.0), libtwolame0, libva1 (>= 1.0.3), libvorbis0a (>= 1.1.2), libvorbisenc2 (>= 1.1.2), libvpx3 (>= 1.5.0), libwavpack1 (>= 4.40.0), libwebp5 (>= 0.4.3), libx264-148, libx265-79 (>= 1.9), libxvidcore4 (>= 1.2.2), libzvbi0 (>= 0.2.35), zlib1g (>= 1:1.2.0)

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The educated differ from the uneducated as much as the living from the
dead. -- Aristotle 
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