Extracting meta-data from a file:

ffmpeg -i INPUT -f ffmetadata FFMETADATAFILE

Injecting meta-data in to files:

ffmpeg -i INPUT -i FFMETADATAFILE -map_metadata 1 -codec copy OUTPUT

• FFMPEG documentation

File format

Hashes and newlines apparently must be escaped with backslashes.

;FFMETADATA1

Version tag.

[CHAPTER]
TIMEBASE=n/d
START=s
END=e
title=name

• n: numerator of time code
• d: denominator of time code
• s: time code chapter begins
• e: time code chapter ends

A timecode of 1/1 means full seconds.