[ 源代码： ttconv ]
软件包：python3-ttconv（1.1.0-1）
library and tool for converting timed text or subtitle formats
ttconv is a library and command line application written in pure Python for converting between timed text formats used in the presentations of captions, subtitles, karaoke, etc.
Input formats: TTML / IMSC, SCC / CEA 608, EBU STL, SRT
Output formats: IMSC / TTML, WebVTT, SRT
Note, that the tool is called ttconv, not tt, i.e. use it like this:
ttconv convert -i subtitles.ttml -o subtitles.srt