The reason you see people planting rice seedlings in wet fields in movies and TV is that the rice being planted is already the second or third crop of the year.

The reason you see people planting rice seedlings in wet fields in movies and TV is that the rice being planted is already the second or third crop of the year. Someone somewhere sowed rice seed densely in a single plot, to use to replant several times as much acreage by transplanting. They can also in some cases raise fish in the same terrace, and herbs or other crops on the walls between them. Farmers of Forty Centuries is an out of copyright book from ~1903 that details the findings of a research group from IIRC England who wanted to understand how the Chinese have been farming the same fields for four millennia without exhausting them. They were doing three crops a year back 120 years ago. A lot of it is down to accumulating silt over time by irrigating with silty water, and dredging the irrigation canals every so often to start new fields with the take.