Any chance of png out (image stream) support?

[Selur]

Do you know of a good program or way to "join" separately created video files without re-encoding them, if both files are created using the exact same encoding settings? (I'm using CRF 18.)

No details -> no clue
Your description hardly says anything about the format and settings you use. When using H.264, streams might need the same SPS/PPS to be append-able. Level&Profiles need to be the same. GOP type (closed vs. open),....

Cu Selur