Upload mp4 and 3gp video, just have voice but no picture

Hello,

I upload mp4 and 3gp video, just have voice but no picture.

The recorded MP4 video files from smartphones, upload to stream server,

just have voice but no picture.

But I download mp4 and 3gp videos from youtube through third-party software,

only mp4 have picture, the 3gp videos still no picture.

Can someone tell me why, and how to solve it?

Thanks!!