1. The reason why sound and image are not synchronized is that the audio sampling rate is not appropriate!
When converting video formats, pay attention to adjusting the audio sampling rate, and always find a synchronization range. (Turn it up or down. Just try it. It is a synchronization range, not a point. )
2. It has something to do with the video you downloaded. Is it like this when playing on the computer? When using the converter, adjust the number of frames to a minimum, so that the phone will not get stuck. If the phone is smart, you can download another playback software to try.