ffmpeg convert mkv to mp4 but keep original sound track

I know this process can be done in 5 or so seconds per file, but every set of steps I find with searches produces files that are much smaller or sometimes even much larger than the originals so the conversion is NOT the 'no changes' conversion I want. I know enough about file sizes, compression, bits, dynamic range, black and white levels (for HD and UHD) to know I can't get the same quality from a 5 GB MKV into a 2.5 GB MP4. Original file size could be 5 GB but the converted file is ALWAYS much smaller. The instructions for using VLC to do this come closest to working, but the file sizes change drastically. I don't want to change the audio during conversion either.Įvery search turns up enthusiastic 'instructions' that NEVER produce the 'no changes' results I'm looking for. The audio of the MKV files can be PCM stereo, Dolby Stereo, and any common consumer home theater audio format from 2.0 to 11.2 so some are Atmos/TrueHD or DTS-HD/DTS:X, others are normal 5.1 or 7.1 soundtracks. I don't want to upconvert or downconvert anything during the conversion. I don't want to change the frame rate or grayscale steps when the files are converted. Black levels are at 16/64 and white level at 235/940. These are all normal 'consumer video' recorded to network hard disks.

There are 2 kinds of MKV files: 1080p video in 24, 30, or 60 fps with h2p video in h265 with 24, 30, or 60 fps. I have MKV files that play properly except on an LG TV that only wants to see MP4.

Doesn't have to be special LG video format or anything, just a normal MP4 file that has the same audio format as the original. Every search result returns options that are slow and do too much and don't provide the SIMPLEST conversion (no changes to the original other than making a copy compatible with MP4. This should be simple as hell, but the internet appears to be brain-dead on this topic.

Ffmpeg convert mkv to mp4 but keep original sound track