The reason was that segments of hls are not png files, but they have headers (first 8 bytes) like png files. I just removed first 8 bytes, and it works. Source: https://github.com/xbmc/inputstream.ffmpegdirect/issues/100?ysclid=m5feoz1irw450917629#issuecomment-828988158

The only questions are:

1. Why does the streaming server mask video segments? Perhaps for security reasons?
2. What other formats do streaming servers use to hide video files?