Convert from .mp4 to .mkv

[chronofusion]

I want the END resulting video file that I convert from whatever to mkv to show " videofilename.mkv" and actually be treated like that in Windows explorer under " Sort by file type".
Thus I want " Encapsulation" to be mkv.
HOWEVER, it seems that no matter what audio setting I use to convert my video files with ( and they play perfectly fine), although the LENGTH of the video file is only 1 hr 36 minutes, I see on the vlc media player " timeline " bar as I call it that it is -13:27:21 meaning 13 hours 27 minutes and 21 seconds. ( wth? )

I see an error message at bottom in the settings menu of "This muxer is not providing directly by VLC: It could be missing." However, again the video file plays perfectly and I can left click on the timeline bar to anywhere during the video file to manually " skip" ahead and backwards as needed without too much lag.
Tried the following combos:
1. Keep original video and audio tracks.
2. Keep original video, mpeg audio

Same results. everything is PERFECT except vlc thinking the movie is 13 ish hours long when it's really 1 hr 26 ish minutes.

Is there a settings adjustment for this and am I missing something simple? This is the ONLY issue i have encountered since I want ALL of my video files to be consistent including the container type to be mkv. VLC noob here but LOVE it and ONLY use it to play movies.

Thanks for the help

[chronofusion]

Nevermind. I figured out mkvmerge does EXACTLY what I need.