The ffmpeg/libav mess is the gift that keeps on giving. The OP appears to be using the obsolete ffmpeg included in jessie's libav-tools package without also using get_iplayer's --ffmpeg-obsolete option to avoid the attendant problems. The latest release of get_iplayer handles this, but for now either use --ffmpeg-obsolete or get a modern version of ffmpeg (get_iplayer installation instructions tell you how).
Also, --vmode is just an alias for --tvmode, as --amode is for --radiomode. A compatibility relic in original code.
