[FFmpeg-user] Muxing private stream into/from mp4 and mpegts

[John Black]

Suppose I have a new track (that is neither audio nor video nor subtitles)
and I want to mux into an existing mp4 file or extract from an mp4 file.
 Or I want to mux into/from mpegts.

Can ffmpeg do this for me without source mods?  I'm going to guess the
answer is "no" but thought there might be some obscure feature I haven't
run across.

Thanks in advance!

John