Basically: some stuff you can put only in MKV, but not in MP4. So, converting "quickly" isn't always an option, if the video/audio formats are not compatible with MP4, you need to re-encode/transcode it to another format. Audio encoding is usually very fast, but video encoding that can take LONG.
Step 1: Open the VLC app and go to the Video tab from the bottom. Then VLC will detect the video files on your iPad including MKV files. Step 2: Tap the MKV video that you want to watch to open it in the player screen. Step 3: Once you press the Play icon, the MKV will be playing on your iPad smoothly.
But MKV and MP4 can also contain H.265 (or other newer video types), that older TVs can't digest. In those cases you will have to convert the video to the older H.264 video format. The FFmpeg app can also do that. The VLC video player app can show what type of video that is inside each video file.
Choose a destination and name your .mp4 file. Click the Browse button at the bottom, then choose a location to which you'd like to save the ripped video file. Then, type a name for the file, and make sure it ends with .mp4. If you don't add .mp4 to the end of the file name, VLC will just play the DVD instead of ripping it.
First, download ffmpeg via homebrew or your favorite method. Then, remux the MKV to an MP4. This should be quite fast because it's not doing any re-encoding: ffmpeg -i <>.mkv -map 0 -codec copy -c:s mov_text -tag:v hvc1 <