Linker error with ffmpeg - qt

Question

I'm trying to build a really simple Qt program using FFMpeg library.
Currently I just want to open and close a video file.
Here is my project file:
QT += core gui
TARGET = avtest01
TEMPLATE = app
INCLUDEPATH += /usr/local/include
LIBS += -L/usr/local/lib -lavformat
SOURCES += main.cpp
And my code:
#include <QDebug>
extern "C" {
#include <libavformat/avformat.h>
}
int main(int argc, char *argv[])
{
if(argc > 1)
{
AVFormatContext *format_context;
qDebug() << argv[1];
if(avformat_open_input(&format_context, argv[1], NULL, NULL) == 0)
{
qDebug() << "open";
avformat_close_input(&format_context);
}
else
qDebug() << "error opening " << argv[1];
}
return 0;
}
Unfortunately, the linker fails:
Undefined symbols for architecture x86_64:
"avformat_open_input(AVFormatContext**, char const*, AVInputFormat*, AVDictionary**)", referenced from:
_main in main.o
"avformat_close_input(AVFormatContext**)", referenced from:
_main in main.o
I'm using Qt 5.1.0 on MacOS.

Answer 1

Your code worked for me after I added av_register_all(); to main.
My guess is that you have avformat compiled for 32 bit. You can confirm by running file /usr/local/lib/libavformat.dylib in terminal.
The output should look like:
/usr/local/lib/libavformat.dylib: Mach-O 64-bit dynamically linked shared library x86_64