Some hardware is not capable of smooth playback of video with fractional frame rate like 23.976Hz. For example, all pre-Haswell Intel GPUs play 23.976Hz video at 24.000Hz and you get a repeated frame every 40 seconds. AMLogic also had this issue (but AFAIK it was fixed with some kernel patches).
I was wondering if Allwinner hardware is capable of properly displaying 23.976 fps video.
I guess monitor has to support it, fractional frame rate has to be whitelisted and resolution switching at start of playback has to be enabled to actually see if this is the issue or not?
Do you know what is actually the reason why some hardware supports it or not? I imagine it has to do which pixel clocks are supported. If that is the case then there is a good chance it will work. I specially took care that as much pixel clocks are supported as possible with Allwinner DW HDMI driver.
Sorry that I can't be more helpful. Currently I don't have appropriate monitor at hand to test it.