Make the one-time initialization in av_get_cpu_flags() thread-safe. The
static variables |flags|, |cpuflags_mask|, and |checked| in
libavutil/cpu.c are read and written using normal load and store
operations. These are considered as data races. The fix is to use atomic
load and store operations.

Remove the |checked| variable because the invalid value of -1 for
|flags| can be used to indicate the same condition. Rename |flags| to
|cpu_flags| and move it to file scope.

The fix can be verified by running the libavutil/tests/cpu_init.c test
program under ThreadSanitizer:
    ./configure --toolchain=clang-tsan
    make libavutil/tests/cpu_init
    libavutil/tests/cpu_init

There should be no warnings from ThreadSanitizer.

Co-author: Dmitry Vyukov of Google, who suggested the data race fix.
Signed-off-by: Wan-Teh Chang <wtc@google.com>

This fixes compilation after the next version bump.

This is the standard behavior for external libraries.

This allows expressing dependencies in a more correct way.

This implements Spherical Video V1 and V2, as described in the
spatial-media collection by Google.
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

While no decoder currently exports spherical information, this type
represents a frame property that has to be passed through from container
to frames.
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

Fill it with AVStereo3D and AVDisplayMatrix documentation.
Apply the necessary changes to make verbatim code look good in doxygen.
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

Otherwise builds without explicit target result in silent no-ops.

This makes sense and takes care of missing build dependencies.

The library versions are stored in the config.mak file and are used
to derive shared library names.

-pie was added to C flags for ThreadSanitizer in commit
19f251a2. Under clang 3.8.0, the -pie
flag causes a compiler warning and a linker error when running configure
--toolchain=clang-tsan. Here is an excerpt from config.log:

clang ... -fsanitize=thread -pie -std=c11 -fomit-frame-pointer -pthread -c -o /tmp/ffconf.A8SsaoCF.o /tmp/ffconf.JdpujQlD.c
clang: warning: argument unused during compilation: '-pie'
clang -fsanitize=thread -pie -Wl,--as-needed -o /tmp/ffconf.2iYA4bsw /tmp/ffconf.A8SsaoCF.o -lm -lm -lbz2 -lz -pthread
/usr/bin/ld: /tmp/ffconf.A8SsaoCF.o: relocation R_X86_64_PC32 against undefined symbol `atan2f@@GLIBC_2.2.5' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: Bad value
clang: error: linker command failed with exit code 1 (use -v to see invocation)

To be conservative, I changed -pie to -fPIE. But the documentation seems
to imply just -fsanitize=thread is enough:

http://clang.llvm.org/docs/ThreadSanitizer.html
https://github.com/google/sanitizers/wiki/ThreadSanitizerCppManualSigned-off-by: Wan-Teh Chang <wtc@google.com>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

The generic parameter names used for CFLAGS in configure must be filtered
for each compiler and replaced by the equivalent flag for that compiler.

This simplifies the code.

This ensures that dependencies are resolved correctly. COMPONENT_LIST
can contain parts that depend on previous entries of CONFIG_LIST.

Handle extralibs in the standard way, add missing pthreads dependency.
Also globally check for -fobj-arc with Objective-C compilers since
that option is useful for other Objective-C code as well.

EXTRALIBS contains general and platform-specific extra libraries
that should be part of all linker commands.

The unadorned package name is needed to derive package-related variable names.

Fixes standalone compilation of the libmp3lame encoder.

It is of doubtful utility, adds complexity and no known users exist.

Supporting the system was a nice joke for the 9 release, but it has
run its course. Nowadays Plan 9 receives no testing and has no
practical usefulness.

The libdc1394 API transition was finished close to a decade ago.