Hi there.
I just join the community, aleready ordered my Mini 3 pro and waiting it to arrive (playing with a friend's Spark untilm my drone arrives).
I am all over the web searching for the information about file size of the mini 3 pro and I can't find it anywhere.
Thinking in 4k/24fps/D-cinelike/H265, what is the file size of a minute of video? Does 64Mb card handle one battery plus flight or do I need a 128Mb card?

Thank you all for the attention.

64mb or 128mb will last you about 5 seconds.      You really need to get 128GB card

I think you made a typo here
Gb.

I use a 256GB SD Card in my Mini 3 Pro and never worry about running out of space during a flight and filming.  

I think to have a card for each battery. Every time I need to land to change battery, I want to change card as well. This is a way to minimize loss footage, for crash (practice so this never happens) os data/card corruption. As a photographer I prefere many smaller cards them a single huge one. Same thing as cinematographer.

I Received this message from DJI:

In 4k/24fps/D-cine like (10bit)/H265, the size of a 1-minute file still is around 700MB. The relevant team has tested with the same parameters, and the footage is around 677MB.


Because the color progression of 10bit is 4 times that of 8bit, color blocks are not easy to appear. At the same time, because the difference between adjacent colors is smaller, it is difficult for the human eye to see the boundaries between color blocks. Although it intuitively feels that 10bit takes up 25% more data than 8bit, in practice 10bit often brings a higher compression rate.
 
Although it intuitively feels that 10bit takes up 25% more data than 8bit, in practice 10bit often brings a higher compression rate. This is because 10bit can describe colors more accurately and improve the signal-to-noise ratio. For example, in order to solve banding, 8bit encoding technology can blur the edge of the color block by a method called dither (dither), that is, the color points of the adjacent colors are mixed in the edge of the color block. However, due to the existence of these color points, the complexity of the picture is greatly increased, and a lot of redundant information is generated. Since 8bit must use these technologies to improve visual perception, 8bit encoding often introduces a lot of redundant information, and 10bit can achieve the same picture experience without dither, so the size of 10bit encoded video is often smaller than the same quality 8bit video.