Hello.
I tested VLC (Android, nightly) with some not very well tested formats. Files are muxed using ffmpeg.
(Note: Coming from GNU/Linux, Android's reliance on file extensions to detect types is a kind of dumb. But that's not a VLC issue.)
1- NUT
files not recognised as is. A rename to some (unrelated) known extension is required. No duration/seek support.
2- ISMV
files not recognised as is. A rename to some known extension is required. Renaming to MP4 is technically correct of course.
3- MP4 with fragments (including ISMV)
Very long videos (1.5h+) created with ffmpeg's '-movflags frag_keyframe' or any other setting that creates a lot of fragments.
Those files take a lot of time to start playing or to create a thumbnail for them. Sometimes VLC crashes due to a timeout.
Seeking time (at least in the betas) is also very slow. But I think that's fixed in nightlies (tested frag_keyframe only).
Otherwise, VLC for Android has come a long way since its early days. So thank you developers and contributors for the great work you've done.