How to Convert MKV to MP4 on Linux

Step-by-step instructions

1. 1

   Install FFmpeg

   Ubuntu/Debian: sudo apt install ffmpeg. Fedora/RHEL: sudo dnf install ffmpeg. Arch Linux: sudo pacman -S ffmpeg. Most distributions have FFmpeg in their official repositories. Verify installation: ffmpeg -version

   Go to converter
2. 2

   Lossless remux (fastest — zero quality loss)

   ffmpeg -i input.mkv -c copy output.mp4. This remuxes the video without re-encoding. Takes seconds regardless of file length. Works when MKV contains H.264 or H.265 video and AAC, MP3, or AC3 audio. If you get errors about incompatible audio, add -c:a aac to convert audio to AAC.

3. 3

   Re-encode to H.264 MP4 (maximum compatibility)

   ffmpeg -i input.mkv -c:v libx264 -crf 18 -preset slow -c:a aac -b:a 192k output.mp4. Use this when the source has incompatible codecs or when you need maximum device compatibility. '-crf 18' is visually lossless quality. Lower CRF = higher quality, larger file.

4. 4

   Hardware-accelerated encoding (NVIDIA NVENC)

   ffmpeg -i input.mkv -c:v h264_nvenc -preset p5 -cq 18 -c:a aac output.mp4. For AMD GPU: -c:v h264_amf. For Intel Quick Sync: -c:v h264_qsv. Hardware encoding is 5-20x faster than software encoding but may produce slightly larger files at the same quality.

5. 5

   Batch convert entire folder

   for f in /path/to/folder/*.mkv; do ffmpeg -i "$f" -c copy "${f%.mkv}.mp4"; done. This remuxes every MKV in the folder. To process subdirectories: find /path/to/folder -name '*.mkv' -exec sh -c 'ffmpeg -i "$1" -c copy "${1%.mkv}.mp4"' _ {} \;