for example i downloaded 2 files from Netflix both has the same lengh 22:02 but when playing with Vlc Player the video will play up to 22:06 so we have 4 seconds of black screen i used Mkvtoolnix and it seems to be that the audio track is bigger than video by a couple of seconds so is that a bug or what ?
It's quite common for the video and audio portions of a media file to differ by a couple of seconds in length. That's nothing to worry about. But if the audio is considerably shorter than the video by say 15-20-30 seconds or more, then you've encountered a known bug in AnyStream which will hopefully be fixed in the next version.