FFmpeg on Android with Rubberband

Question

When I try to link librubberband.a I get: libavfilter/af_rubberband.c:236: error: undefined reference to 'rubberband_set_pitch_scale'

1. I compiled rubberband for armv7a, and created a static library (rubberband.a). I checked the library, and It contained the needed symbols (using nm).

2. I verified that librubberband.a is in the libpath (-L)

3. 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.