[FFmpeg-user] What are the the data and attachment stream type?

[Guofeng Zhang]

Hi,

The book "FFmpeg Basic" described that FFmpeg recognizes 5 stream types:
audio (a), attachment (t), data (d), subtitle (s) and video (v).

I do not understand what the data and attachment type specified and what
they are used for.

Is there any introduction about data and attachment stream type on the
internet?

Thanks for your help!

Guofeng