# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/^(\d{1,2}:\d{2}:\d{2})\.(\d{3}[-> ]+\d{1,2}:\d{2}:\d{2})\.(\d{3})/\i\n$1,$2,$3/gm;t' <<< "0:01:00.340 --> 0:01:01.380
***subtitle text***
0:01:01.380 --> 0:01:02.390
***subtitle text***"
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html