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I need to convert a video file from Matroska container into mp4 container. Matroska file contains one h.264 video track and one AC3 sound track. It should be possible to do this losslessly, but how to do it with native Ubuntu tools?

Transcoding is not an option.

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  • See this question.
    – Binarylife
    Commented Jun 24, 2011 at 23:30
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    this is especially a solution for converting Matroska files that won't play in a Samsung TV, to files that are compatible with it
    – knocte
    Commented Oct 7, 2015 at 23:47
  • Over the years I've found this very useful as Chromecast supports H.264 with AAC or MP3 in an MP4 container. It is very easy to stream videos from your computer to Chromecast if you have Chrome with the Google cast extension. Just drag and drop an MP4 with correct stream encodings to a browser window and start streaming.
    – Seppo Erviälä
    Commented Jun 24, 2016 at 0:17

7 Answers 7

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Perhaps the easiest tool for that is ffmpeg, or avconv from the libav-tools package. Libav is a fork of FFmpeg, which Ubuntu switched to for a few years until Ubuntu 15.04. It is one of the backends for many of the GUI tools mentioned in other answers.

Changing container without re-enconding content could not be simpler:

ffmpeg -i input.mkv -codec copy output.mp4

  • It auto-detects a Matroska to MP4 container conversion based on input/output filenames.

  • -codec copy stream copies, or "re-muxes", the streams from the input to the output without re-encoding. Think of it like a copy and paste between containers.

  • Default stream selection behavior is to select only one stream per stream type. For example, if your input has two video streams and one audio stream then only the video stream with the largest frame size will be selected. Add -map 0 if you want to select all streams from the input.

  • Some containers may not support some formats. So check if your chosen container format, be it mkv, mp4 or even avi has support for all the content in your files (video, audio, subtitles, data, etc). For example, mp4 does not support SubRip subtitles (.srt files).

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    To transcode the audio to AAC, leaving the video as AVC: avconv -i input.mkv -c:v copy -c:a libfaac output.mp4 (I used ffmpeg, I assume avconv has the same command line args here)
    – camh
    Commented Oct 23, 2012 at 2:42
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    If you want to transfer both the video and audio (both losslessly) and for it not to choke on subtitles then: avconv -i input.mkv -c:v copy -c:a copy -sn output.mp4. MP4 supports the most of the common audio formats used in MKVs including MP3 and AAC.
    – thomasrutter
    Commented Jan 25, 2013 at 2:39
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    @AquariusPower: just be aware that the OP does not want to remap the streams: he wants to convert the container only and keep all streams.
    – MestreLion
    Commented Sep 15, 2015 at 20:58
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    @AquariusPower: have you tried simply with -map 0 to get both audio streams? As I said in the answer: "Default stream selection behavior is to select only one stream per stream type"
    – MestreLion
    Commented Sep 16, 2015 at 5:26
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    @camh: FFmpeg removed libfaac support in 2016, instead using native, built-in FFmpeg AAC encoder. "ffmpeg -i input.mkv -c:v copy -c:a aac output.mp4"
    – chiappa
    Commented Mar 24, 2020 at 23:22
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Get needed software

sudo apt-get install gpac mkvtoolnix

Extract video and audio from matroska file

First you need to check what tracks the matroska file contains with

mkvmerge --identify video.mkv

File 'video.mkv': container: Matroska
Track ID 1: video (V_MPEG4/ISO/AVC)
Track ID 2: audio (A_AC3)

Then extract video and audio according to their tracks with:

mkvextract tracks video.mkv 1:video.h264 2:audio.ac3

Extracting track 1 with the CodecID 'V_MPEG4/ISO/AVC' to the file 'video.h264'. Container format: AVC/h.264 elementary stream
Extracting track 2 with the CodecID 'A_AC3' to the file 'audio.ac3'. Container format: Dolby Digital (AC3)
Progress: 100%

Mux audio and video into mp4 containter

MP4Box -fps 24 -add video.h264 -add audio.ac3 video.mp4

AVC-H264 import - frame size 1280 x 720 at 24.000 FPS
Import results: 31671 samples - Slices: 5672 I 125048 P 122648 B - 32288 SEI - 4936 IDR
AC3 import - sample rate 48000 - 6 channels
Saving to video.mp4: 0.500 secs Interleaving

I had to add -fps 24 option because MP4Box didn't detect video fps correctly. Depending on usage AC3 audio track should be re-encoded into something else before muxing.

Now you have remuxed streams from matroska container into mp4 container without losing any quality.

EDIT: MP4 doesn't officially support AC3 audio so the audio track should be converted into a supported format (eg. AAC, MP3) if you want the file to be playable with something else than VLC.

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15

You can use Avidemux

It has good GUI interface.

When converting from mkv to mp4 it is not re-encoded.

The convertion is done within a minute (for a 60-min video).

  1. sudo apt-get install avidemux

  2. Open the mkv file in avidemux.

  3. Select safe mode if prompted.

  4. Leave the video as copy.

  5. Choose File-> Properties. Check if the audio codec is aac.

    1. If audio codec is NOT aac, select aac(faac).
    2. Otherwise, leave it as copy. (Sometimes using this option the audio may be out of sync or distorted, in that case select aac(faac) instead.)

  6. Select mp4 for format.

  7. Select save, choose location and type a filename with .mp4 as the extension.

Note: Sometimes (~10% chance) it may fail. Then use handbrake(re-encode).

Note2: there are two links which help you:

http://www.ubuntugeek.com/avidemux-free-video-editor-designed-for-simple-cutting-filtering-and-encoding-tasks.html

http://www.ubuntugeek.com/how-to-convert-mkv-file-into-mp4-file-using-avidemux.html

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  • Worked like a charm. I had sync problems following the accepted answer, but not with this one.
    – moraes
    Commented Oct 28, 2012 at 13:29
  • works very well
    – psychok7
    Commented Jan 8, 2017 at 17:09
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enter image description here

You can use my application, dmMediaConverter. Just leave "copy" for both streams checked (no transcoding) and put .mp4 to the output file name. That's it. Very simple. http://dmsimpleapps.blogspot.ro/2014/04/dmmediaconverter.html

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    Thank you for this great tool! - Note: on multiple occasions, when the mkv had internal subs, I had to change the codec to mov_text.
    – cipricus
    Commented Jan 18 at 15:45
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Using ffmpeg i write a python script that will convert all the mkv files of the current directory to mp4 files as converting them one by is annoying.

Can use it if needed.

Convert MKV to MP4

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  • Or you can convert all the .mkv files with the following command: for f in *.mkv; do ffmpeg -i "$f" -c copy "${f%.*}.mp4"; done
    – alexg
    Commented Aug 18 at 10:54
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You can try HANDBRAKE by adding its PPA by typing this code into the terminal:

sudo add-apt-repository ppa:stebbins/handbrake-releases
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  • This seems to be a video transcoder. I do not want to compress the video track again as it is already in h.264 format.
    – Seppo Erviälä
    Commented Jun 25, 2011 at 9:09
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    Handbrake is a great transcoder, but I would never use it for file format conversion.
    – CyberSkull
    Commented Mar 15, 2012 at 13:39
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    I absolutely love Handbreak, but unfortunately it only works losslessly for audio (and subtitles). I couldn't find a way to copy the video without transcoding it, and the OP specifically requested lossless format conversion.
    – MestreLion
    Commented Oct 3, 2012 at 22:10
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Since MPEG Part 14 supports h.264 and AC3 natively without transcoding, you can simply rename the file so it has an .mp4 extension instead of a .mkv extension.

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    It might support the codecs inside, but that doesn't mean it will work in an application that doesn't understand Matroska. This would only work if the application supports Matroska and looks at the magic number instead of the extension.
    – Arda Xi
    Commented Sep 20, 2015 at 14:58
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    Renaming the file will not convert the container format, and it might confuse the application (and users). As @ArdaXi said, the application would still need to support Matroska to play it.
    – MestreLion
    Commented Feb 13, 2016 at 12:37

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