Iam using libVLC in my application but what I will describe is observed in full VLC app as well.
When you looping same video or you have playlist of medias with same pixel resolution (and type) VLC can go between them in gapless mode (no black between- straight from last frame to first frame of next media).
If media have different pixel size or media resolution is over some size (think its around ~4k) it make short black gap between media.
Would be possible to change this behavior?
Maybe keep last frame inside player object (until first frame from new media is ready to be play) or increase buffer or whatever is responsible that this gapless playback dont work with media over 4k?