@bodo said:
should be able to play one mp4 (i know hap is better) ....???? are there any known incompatibility with izzy
Yes, but there are various ways that different software can spit out mp4 files. There are known issues with certain quirky things like embedded timecode tracks and the h265 codec that can cause issues in Isadora, which is why our first suggestion is always to transcode any media files that are misbehaving in Isadora.