Merging mkv files

A while ago I was looking for a way to merge two separate .mkv files (left and right views of a stereoscopic, 3D movie) into one file, to get a side-by-side or top-bottom view. Since back then I didn’t get any answer on SuperUser I’ve got an answer, I figured I might just look into it myself, google it, read a few man pages, and then write it down for the rest of the world.

I’m not encouraging anyone to download pirated films. But, if you do have the movies, and they are in separate files, but you want to watch them on a 3DTV or a PS3 that can only play side-by-side, single-file 3D movies, you’ll end up merging your files.

If you just want to know how to merge these files using the GUI, I’m not going to write it down here, as there exists a very detailed tutorial about this over at Ameic.net. Go read that if you want to do this using the GUI.

If you’d rather do it in the command line though (which would allow you to create a batch to process all your movies later, nice the process while you’re working on the computer, and ler it rock while you’re away), read on.

Here’s what you’re going to need:

  • mkvtoolnix
  • ffmpeg
  • avisynth

mkvtoolnix is a free, open source tool. In Gentoo, you can get it from Portage. ffmpeg is also available for Gentoo. You can find out more about Avisynth on their home page.

$ sudo emerge -at mkvtoolnix

Note that if you build it yourself, there’s also an --enable-qt option, but for some reason a qt use flag does not exist in the ebuild. Also, I don’t build ffmpeg here as I already have that on my system.

Next thing you’ll need to do is extract the audio you want. Use eac3to to do so:

$ eac3to video-left.mkv sound.ac3

Update 1

As Marcin mentioned, you can extract the autio simply using ffmpeg, you don’t need eac3to:

$ ffmpeg -i video-left.mkv -acodec copy audio.ac3

Next thing you’re going to do is extract the video streams of both left and right files, and convert them to side-by-side view. To do so, you’ll need to generate an .avs file that looks like this:

videol=DirectShowSource("/path/to/video-left.mkv")
videor=DirectShowSource("/path/to/video-right.mkv")
video=StackHorizontal(videol, videor)
BicubicResize(video, 1920, 1080)

Name this file convert.avs, then process it with ffmpeg like this:

$ ffmpeg -i convert.avs -vcodec libx264 -b 7500000 -bt 7500000 -y video-sbs.h264

Now merge the audio and the video:

$ mkvmerge -o result.mkv --default-duration 0:24000/1001fps video-sbs.h264 audio.ac3

The resulting result.mkv file can now be played on a 3DTV or a PS3. You can now remove the temporary files:

$ rm sound.ac3 video-sbs.mkv convert.avs

Update 2

I’ve just got an answer on SuperUser. In short, here’s how no do it with GStreamer:

$ gst-launch-0.10 \
    filesrc location=MVI_0735L.MOV ! decodebin2 name=Left \
    filesrc location=MVI_0735R.MOV ! decodebin2 name=Right \
    Left.  ! videoscale ! ffmpegcolorspace ! video/x-raw-yuv, width=1280, \
             height=720 ! videobox border-alpha=0 right=-1280 ! queue ! mix. \
    Right. ! videoscale ! ffmpegcolorspace ! video/x-raw-yuv, width=1280, \
             height=720 ! videobox border-alpha=0 left=-1280 ! queue ! mix. \
    Left.  ! decodebin2 ! audioconvert ! audiopanorama panorama=-1.00 ! \
             queue ! addaudio. \
    Right. ! decodebin2 ! audioconvert ! audiopanorama panorama=1.00 ! \
             queue ! addaudio. \
    adder name=addaudio ! faac ! avmux. \
    videomixer name=mix ! ffmpegcolorspace ! x264enc ! \
    avimux name=avmux ! progressreport name="Encoding Progress" ! \
    filesink location=out.avi