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 encoders)