Go to https://libav.org/download.html
git clone git://git.libav.org/libav.git libav
To enable most features for Linux Mint you will need to install some extra development libraries
sudo apt-get install frei0r-plugins-dev libbs2b-dev libfaac-dev libfdk-aac-dev libgsm1-dev libmp3lame-dev libopencore-amrnb-dev libopencore-amrwb-dev libopencv-dev libopenjpeg-dev libopus-dev libpulse-dev libschroedinger-dev libspeex-dev libtheora-dev libtwolame-dev libvo-aacenc-dev libvo-amrwbenc-dev libvorbis-dev libvpx-dev libwavpack-dev libwebp-dev libxvidcore-dev libssl-dev libcdio-paranoia-dev;
then within the libav folder configure with
./configure –enable-dxva2 –enable-vda –enable-vdpau –enable-libcdio –enable-bzlib –enable-frei0r –enable-gnutls –enable-libbs2b –enable-libdc1394 –enable-libfaac –enable-libfdk-aac –enable-libfreetype –enable-libgsm –enable-libmp3lame –enable-libopencore-amrnb –enable-libopencore-amrwb –enable-libopencv –enable-libopenjpeg –enable-libopus –enable-libpulse –enable-librtmp –enable-libschroedinger –enable-libspeex –enable-libtheora –enable-libtwolame –enable-libvo-aacenc –enable-libvo-amrwbenc –enable-libvorbis –enable-libvpx –enable-libwavpack –enable-libwebp –enable-libx264 –enable-libxvid –enable-openssl –enable-x11grab –enable-zlib –enable-gpl –enable-nonfree –enable-version3
compile with
make
install it with
make install
You should now have the latest avconv installed and up to date.