build: make it easier to force FFmpeg upstream

Apparently some people want this. Actually making it compile is still
their problem, though, and I expect that build with FFmpeg upstream will
occasionally be broken (as it is right now). This is because mpv also
relies on API provided by Libav, and if FFmpeg hasn't merged that yet,
it's not our problem - we provide a version of FFmpeg upstream with
those changes merged, and it's called ffmpeg-mpv.

Also adjust the README which still talked about FFmpeg releases.

README.md

@@ -147,17 +147,14 @@ with FFmpeg only (subtitle formats in particular).
 
 ## Preferred FFmpeg version
 
+Only [ffmpeg-mpv][ffmpeg-mpv] is supported. Upstream FFmpeg can be forced by
+passing a certain switch to configure, but compilation or runtime behavior
+might be broken at times.
 
-Using the latest FFmpeg release (or FFmpeg git master) is strongly recommended.
-Older versions are unsupported, even if the build system still happens to
-accept them. The main reason mpv still builds with older FFmpeg versions is to
-evade arguing with people (users, distros) who insist on using older FFmpeg
-versions for no rational reason.
-
-If you want to use a stable FFmpeg release, use the latest release, which has
-most likely the best maintenance out of all stable releases. Older releases
-are for distros, and at best receive basic changes, like fixing critical security
-issues or build fixes, and at worst are completely abandoned.
+_If_ you force upstream FFmpeg, and it doesn't work, please contact upstream
+FFmpeg for help, instead of mpv. See
+[FFmpeg contact][http://ffmpeg.org/contact.html#MailingLists] how to contact
+FFmpeg upstream.
 
 ## FFmpeg ABI compatibility
 

audio/aconverter.c

@@ -33,7 +33,7 @@
 #include "fmt-conversion.h"
 #include "format.h"
 
-#define HAVE_LIBSWRESAMPLE HAVE_FFMPEG_MPV
+#define HAVE_LIBSWRESAMPLE (!HAVE_LIBAV)
 #define HAVE_LIBAVRESAMPLE HAVE_LIBAV
 
 #if HAVE_LIBAVRESAMPLE

common/av_log.c

@@ -44,8 +44,7 @@
 
 #if HAVE_LIBAV
 #include <libavresample/avresample.h>
-#endif
-#if HAVE_FFMPEG_MPV
+#else
 #include <libswresample/swresample.h>
 #endif
 
@@ -199,8 +198,7 @@ bool print_libav_versions(struct mp_log *log, int v)
         {"libavfilter",   LIBAVFILTER_VERSION_INT,   avfilter_version()},
 #if HAVE_LIBAV
         {"libavresample", LIBAVRESAMPLE_VERSION_INT, avresample_version()},
-#endif
-#if HAVE_FFMPEG_MPV
+#else
         {"libswresample", LIBSWRESAMPLE_VERSION_INT, swresample_version()},
 #endif
     };

wscript

@@ -458,21 +458,22 @@ libav_dependencies = [
         'req': True,
         'fmsg': "FFmpeg/Libav development files not found.",
     }, {
-        'name': 'ffmpeg_mpv',
+        'name': 'ffmpeg-mpv',
         'desc': 'libav* is FFmpeg mpv modified version',
         'func': check_statement('libavcodec/version.h',
                                 'int x[LIBAVCODEC_MPV ? 1 : -1]',
                                 use='libavcodec')
     }, {
-        'name': 'ffmpeg_garbage',
-        'deps': '!ffmpeg_mpv',
+        'name': '--ffmpeg-garbage',
+        'deps': '!ffmpeg-mpv',
         'desc': 'libav* is upstream FFmpeg (unsupported)',
         # FFmpeg <=> LIBAVUTIL_VERSION_MICRO>=100
         'func': check_statement('libavcodec/version.h',
                                 'int x[LIBAVCODEC_VERSION_MICRO >= 100 ? 1 : -1]',
-                                use='libavcodec')
+                                use='libavcodec'),
+        'default': 'disable',
     }, {
-        # This check should always result in the opposite of is_ffmpeg.
+        # This check should always result in the opposite of ffmpeg-*.
         # Run it to make sure is_ffmpeg didn't fail for some other reason than
         # the actual version check.
         'name': 'libav',
@@ -484,7 +485,7 @@ libav_dependencies = [
     }, {
         'name': 'libav-any',
         'desc': 'Libav/FFmpeg library versions',
-        'deps': 'ffmpeg_mpv || libav',
+        'deps': 'ffmpeg-mpv || ffmpeg-garbage || libav',
         'func': check_ffmpeg_or_libav_versions(),
         'req': True,
         'fmsg': "Unable to find development files for some of the required \