Tips

Containers - supported subtitle codecs:

MP4 - mov_text

MKV - hdmv_pgs_subtitle

FFmpeg:

Using 2 audio encoders at same time:

-map 0:${input_stream_number} -c:${output_stream_number} mp3 -map 0:${input_stream_number} -c:${output_stream_number} flac

Where the map commands refer to input stream number, and the encoder refers to the output stream number (important when changing number of streams whilst using multiple e.g. audio encoders)