librtmp-dev 2.4+20151223.gitfa8646d.1-2build1 (armhf binary) in ubuntu focal

 A small dumper for media content streamed over the RTMP protocol (like BBC's
 iPlayer high quality streams). Supplying an RTMP URL will result in a dumped
 flv file, which can be played/transcoded with standard tools.
 .
 This package contains the development libraries, header files needed by
 programs that want to compile with librtmp.