I ran into the same problem while using the same ffmpeg-full package. I use this package for specific reasons so I couldn't simply replace it with the arch default. When I did a backtrace in GDB, the debugger showed that there is a problem with libsrt. Since I don't need srt, I simply edited the ffmpeg-full PKGBUILD file for ffmpeg-full and set the --enable-libsrt switch to --disable-libsrt and rebuilt the ffmpeg-full package to workaround the problem.