FFmpeg on Android with Rubberband - ffmpeg

Question

When I try to link librubberband.a I get:
libavfilter/af_rubberband.c:236: error: undefined reference to 'rubberband_set_pitch_scale'
I compiled rubberband for armv7a, and created a static library (rubberband.a).
I checked the library, and It contained the needed symbols (using nm).
I verified that librubberband.a is in the libpath (-L)
I verified that extern C exists in the rubberband.c.h file.
Any ideas?

Answer 1

The error happened in the link stage. Make sure the link directory has been added to -L parameters of your compiler.
-L/directory/of/your/lib
And specify the library with -l option.
So make sure the option -L/directory/of/your/lib -lrubberband set for your compiler when you build ffmpeg with rubberband support.
If you didn't use pkg-config to add the library. You can use the option --extra-ldflags to add when configure ffmpeg before build.
./configure \
# some configure options
--extra-ldflags="-L/directory/of/your/lib -lrubberband" \
# more configure options
If you use pkg-config to find out the libraries. Just add the library.pc directory to PKG_CONFIG_PATH, and let the build system do the remaining.
export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/directory/to/your/rubberband.pc
Updated
Finally make sure you link against to the same architecture of your library.
$ arm-linux-androideabi-readelf -h librubberband.a |grep 'Class\|Machine
For armeabi-v7a, it should be ELF32 and ARM.
Updated
I have cloned the source of rubberband from https://bitbucket.org/breakfastquay/rubberband
And found the function call rubberband_set_pitch_scale is defined at src/rubberband-c.cpp, this file is not include in Android.mk when build for Android (WHY?).
So you have to add this file to build.
RUBBERBAND_SRC_FILES = ... \
$(RUBBERBAND_SRC_PATH)/rubberband-c.cpp
After build done, you need to create directory structure like below
.
├── include
│   └── rubberband
│   ├── RubberBandStretcher.h
│   └── rubberband-c.h
└── lib
├── librubberband.a
└── pkgconfig
└── rubberband.pc
The file rubberband.pc was copied from rubberband.in.pc with some minor changes.
prefix=/path/to/rubberband/install/root
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include
Name: rubberband
Version: 1.8.1
Description:
Libs: -L${libdir} -lrubberband -L/path/to/android/ndk/sources/cxx-stl/gnu-libstdc++/4.9/libs/armeabi-v7a -lgnustl_static
Cflags: -I${includedir}
Then add
export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/path/to/rubberband/install/root
before ./configure to tell ffmpeg find rubberband by pkg-config.
I have tried with the latest ffmpeg, it works.