Receives FFmpeg's own log lines, as installed with FFmpeg.setLogSink.
One line. component names what logged, such as h264 or mov,mp4,m4a,3gp,3g2,mj2, and is empty when FFmpeg names nothing. message is one call of FFmpeg's logger without its trailing newline, so a line FFmpeg builds in parts arrives in parts.
h264
mov,mp4,m4a,3gp,3g2,mj2