Issue with using ffmpeg webport via USE_FFMPEG=1

[twadrianlis]

Hi,

I added ffmpeg to my project. I add USE_FFMPEG=1 flags to compiler and linker (via cmake).

I see ffmpeg correctly downloaded and built in my local .emscripten_cache, in asmjs/port-builds I see ffmpeg directory and all headers as well as libffmpeg-mt.bc

The project builds but during linkage I get unresolved externals errors from avformat library. This is my output:

cmd.exe /C "cd . && C:\emsdk\emscripten-1.39.4.7-windows64\fastcomp\emscripten\em++.bat -DNDEBUG -O2 -O2  -O0 -g3 --source-map-base http://localhost:8000/ -s USE_PTHREADS=1 -s PTHREAD_POOL_SIZE=2 -s USE_SDL=2 -s USE_BOOST_HEADERS=1 -s WASM=1 -s ASSERTIONS=2 -s DEMANGLE_SUPPORT=1 --bind -s TOTAL_MEMORY=256MB -fexceptions --preload-file ../../wasm_data@/ -lwebsocket.js  --shell-file ../tizen/src/shell_minimal.html -s ENVIRONMENT_MAY_BE_TIZEN -s USE_FFMPEG=1 tizen/wasm/CMakeFiles/illusion-tizen.dir/source/Main.cpp.o -o tizen\wasm\illusion-tizen.html  renderer/libillusion-renderer-common.a  dependencies/spdlog/libspdlog.a  dependencies/freetype/libfreetype.a  dependencies/absl/absl/strings/libabsl_strings.a  dependencies/absl/absl/strings/libabsl_strings_internal.a  dependencies/absl/absl/base/libabsl_base.a  dependencies/absl/absl/base/libabsl_spinlock_wait.a  dependencies/absl/absl/numeric/libabsl_int128.a  dependencies/absl/absl/base/libabsl_throw_delegate.a  dependencies/absl/absl/base/libabsl_raw_logging_internal.a  dependencies/absl/absl/base/libabsl_log_severity.a  _deps/zip-build/libzip.a  lib/libhv_static.a  -lpthread  -lm  -ldl && cd ."
error: undefined symbol: _Z18avio_alloc_contextPhiiPvPFiS0_S_iES2_PFxS0_xiE
warning: To disable errors for undefined symbols use `-s ERROR_ON_UNDEFINED_SYMBOLS=0`
error: undefined symbol: _Z19avformat_open_inputPP15AVFormatContextPKcP13AVInputFormatPP12AVDictionary
error: undefined symbol: _Z22avformat_alloc_contextv
error: undefined symbol: _Z7av_freePv
error: undefined symbol: _Z9av_mallocm
Error: Aborting compilation due to previous errors
shared:ERROR: 'C:/emsdk/emscripten-1.39.4.7-windows64/node/12.9.1_64bit/bin/node.exe C:\emsdk\emscripten-1.39.4.7-windows64\fastcomp\emscripten\src\compiler.js c:\users\dasoft\appdata\local\temp\tmplvuacp.txt' failed (1)
ninja: build stopped: subcommand failed.

I have no ideas left. Clearly it has issues with libffmpeg functions like avformat_open_input, avformat_alloc_context etc.

Any ideas?

[abujalski]

Hi,

It looks that you need to wrap ffmpeg headers with extern "C" like:

extern "C" {
#include <libavcodec/avcodec.h>
}

in all your sources, to avoid C++ function name mangling.