JSON correctly converts namedtuples to lists when they appear in list form, but not when used as value in dictionary. Seems to work the same on mpy verion 1.20 - 1.26, running on Pico, Pico2 , Arduino ...
1 00:02:38,910 --> 00:02:40,161 English! I'm English! 2 00:05:40,049 --> 00:05:41,801 It's grenadiers, mate.