I cannot view video files in their entirety on the Dropbox mobile app

i recorded clips on my pc and converted them into mp4 format to be able to save them on my phone. i moves all the clips into my dropbox via computer and all the videos played fine. when i look at the videos in my dropbox on my phone, it only lets me play half the videos and not from the beginning. when i saved the videos to camera roll, the videos played fine on my camera roll but when i put the clips into capcut, they were having the same problem as they were in the dropbox, freezing with only audio for most of it and then playing a little bit of the video. how do i fix this? i am new to dropbox