How to Demux MKV to Extract Raw Video Stream

Demuxing an MKV file to extract its raw video stream is not only possible but also a straightforward process that does not require re-encoding. This article provides a quick guide on how to separate a video track from its MKV container losslessly using two of the most powerful and free multimedia tools available: FFmpeg and MKVToolNix.

Understanding MKV Demuxing

An MKV (Matroska) file is a container format that holds multiple streams, including video, audio, subtitles, and metadata. “Demuxing” (short for demultiplexing) is the process of stripping these streams apart into individual, raw files. Because demuxing merely copies the existing data streams out of the container without altering them, the process is incredibly fast and preserves 100% of the original video quality.

Method 1: Extracting Video Using FFmpeg

FFmpeg is a powerful command-line tool that can extract video streams with a single command.

To extract the raw video stream using FFmpeg, open your command prompt or terminal and run the following command:

ffmpeg -i input.mkv -map 0:v -c:v copy output.h264

Note: Replace .h264 with the appropriate extension for your raw stream, such as .hevc for H.265 video or .m4v for MPEG-4.

Command Breakdown:

-i input.mkv: Specifies the input MKV file.
-map 0:v: Selects only the video stream from the first input file.
-c:v copy: Instructs FFmpeg to copy the video stream directly without re-encoding it.

Method 2: Extracting Video Using MKVToolNix

MKVToolNix is the official suite of tools for handling Matroska files. It includes a command-line utility called mkvextract designed specifically for this task.

First, identify the track ID of the video stream by running: mkvmerge -i input.mkv (This will output a list of tracks, usually showing the video stream as Track ID 0).
Extract the raw video track using the mkvextract tool with the following command: mkvextract tracks input.mkv 0:output.h264

If you prefer a graphical user interface (GUI), you can download a helper application like gMKVExtractGUI. When paired with MKVToolNix, this utility allows you to open your MKV file, check a box next to the video track, and click “Extract” to obtain your raw video file instantly.