The standard community recommendation for this task is using the MKVToolNix GUI . It is specifically designed to handle the Matroska format .
Open MKVToolNix GUI and drag your first file (e.g., 1.mkv ) into the "Source files" section. The standard community recommendation for this task is
Right-click the file you just added and select "Append files" . Select the remaining parts (e.g., 2.mkv and 3.mkv ) in their correct sequential order. The standard community recommendation for this task is
Click "Start multiplexing" (or press Ctrl+R ) to begin the merge. The standard community recommendation for this task is
A single, "long piece" MKV file will be created in seconds because no conversion is taking place. 2. Alternative: Command Line with FFmpeg