Merge MKV Files Using FFmpeg Concat Demuxer

This article provides a straightforward, step-by-step guide on how to merge multiple MKV video files with identical codecs using the FFmpeg concat demuxer. By using this method, you can join your videos instantly without re-encoding, preserving the original quality of your files.

Step 1: Create a Text File of Input Videos

To use the concat demuxer, you must first create a text file listing all the MKV files you want to merge in the exact order you want them to appear.

Create a file named inputs.txt in the same directory as your video files and format it like this:

file 'video1.mkv'
file 'video2.mkv'
file 'video3.mkv'

Alternatively, you can generate this list automatically using your command line terminal.

On Windows (Command Prompt):

(for %i in (*.mkv) do @echo file '%i') > inputs.txt

On macOS and Linux (Terminal):

printf "file '%s'\n" *.mkv > inputs.txt

Step 2: Run the FFmpeg Concat Command

Once your inputs.txt file is ready, open your terminal or command prompt in that directory and run the following FFmpeg command:

ffmpeg -f concat -safe 0 -i inputs.txt -c copy output.mkv

Explanation of the Parameters

-f concat: This tells FFmpeg to use the concat demuxer format.
-safe 0: This flag prevents FFmpeg from rejecting safe file paths, allowing you to use relative or absolute paths inside your text file.
-i inputs.txt: Specifies the input text file containing the list of videos to merge.
-c copy: This stream-copies the audio and video codecs instead of re-encoding them. This makes the merging process almost instantaneous and ensures zero quality loss.
output.mkv: The name of your newly merged final video file.

Important Requirements

For this process to work flawlessly, the source MKV files must have: * Identical video codecs and resolutions. * Identical audio codecs, sample rates, and channel layouts. * Identical timebase and frame rates.

If the files differ in these parameters, the output file may suffer from sync issues, missing audio, or playback errors.