[FFmpeg-devel] [PATCH 1/2] osx: detect version of mac os

[Stefano Sabatini]

On date Friday 2012-08-24 06:48:36 +0800, Xidorn Quan encoded:
> On Fri, Aug 24, 2012 at 1:25 AM, Stefano Sabatini <stefasab at gmail.com>wrote:
> 
> >
> > Also how this belongs to a media library? I mean why this should be
> > defined in a generic library, rather than, say, in a MacOS
> > application/library?
> >
> > For library implementation purposes we only need to know when a
> > feature is available or not, and this is done during the configuration
> > stage.
> 
> 

> So why do you have libavutil/cpu.c belonging to ffmpeg? Why do you
> need to detect CPU flags on the runtime? Shouldn't it be done during
> the configuration stage?

CPU flags are not dependent on the OS system. Also there are some
cases when you want to get fine grained features at run time (e.g. =>
HAVE_SSE => SSE, SSE2, SSE3 SSSSE3 etc.). I suppose this could be done
at the configuration stage as well, can't really comment why it is
done this way).

But the main issue is that if we accept this, we would have to accept
then av_get_linux_version(), av_get_bsd_version(),
av_get_windows_version(), av_get_android_version() etc. etc. ad
nauseam.

A possible solution would be to have an av_get_os_version(), but given
that it might be hard to get a common scheme (e.g. name, family,
major, micro, minor) for all OS/kernels then for fixing this case a
local solution might be more suitable.

...

Elaborating more on this:

    /* init pix_fmts of codec */
+    if (!ff_h264_vda_decoder.pix_fmts) {
+        int major, minor, bugfix;
+        if (!av_get_osx_version(&major, &minor, &bugfix)) {
+            av_assert0(major == 10);
+            av_log(avctx, AV_LOG_VERBOSE, "Detected system version: %d.%d.%d\n",
+                    major, minor, bugfix);
+            if (minor < 7)
+                ff_h264_vda_decoder.pix_fmts = vda_pixfmts_prior_10_7;
+            else
+                ff_h264_vda_decoder.pix_fmts = vda_pixfmts;
+        } else {
+            av_log(avctx, AV_LOG_WARNING,
+                    "Failed to determine system version.\n");
+            ff_h264_vda_decoder.pix_fmts = vda_pixfmts;
+        }
+    }

Possible solutions I see:

* configuration stage detection, you could use check_code() and define
  HAVE_MACOSX_VDA_PIXFMTS or whatever

* you add a static function in you implementation:

#if HAVE_MACOSX_FOOBAR
static int get_osx_version(...)
{
...
}
#endif

...

#if HAVE_MACOSX_FOOBAR
        if (get_osx_version(&major, &minor, &bugfix)) {
            av_assert0(major == 10);
            av_log(avctx, AV_LOG_VERBOSE, "Detected system version: %d.%d.%d\n",
...
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