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If you receive a message that the “File format is not supported” when playing back a .mkv file, it may be because the file was created with header compression, which prevents playback on devices that do not support that feature. Unfortunately, the list of such devices is long.
Serviio can attempt to transcode these files into a different, playable format (if profile.xml has mkvHeaderCompressed=“true” in the appropriate Matches element), but transcoding degrades the quality. Instead of relying on Serviio to transcode the file upon playback, you should remux the file, creating a new one that has the same video and audio data, just without the compression.
You can use MediaInfo to verify whether there is header compression. To remove the compression, you can use mkvmerge.
Remuxing does not re-encode the video or audio data, it just recombines and reorganizes the existing digital information, changing only the way it is arranged in the file. The bits and bytes that make up the video and audio parts of the file are not changed and therefore are not degraded in any way; the quality of the remuxed file is identical to the original.
The demuxing/remuxing process takes less than 30 seconds of computer time per Gigabyte (depending on the speed of your computer). Only slightly longer than the amount of time it takes to make a copy of the original video file.
You need to download and install MKVToolNix from http://www.bunkus.org/videotools/mkvtoolnix/
This will give you several tools for manipulating MKV files. You'll only be using mkvmerge, which, despite its name, can be used for more than just merging.
Run the mkvmerge GUI (mmg or mmg.exe).
Add the MKV file by Drag 'n Dropping into the “Input files” section or by using the “add” button.
All video, audio, subtitles (subtitles are actually video tracks), and any other track that will allow “Compression” to be changed, must be changed to “none” to insure that the video will play properly.
When muxing completes, close mkvMerge and play the file with your favorite media player or standalone device. The original file may be deleted when the new file is tested and deemed proper.
Each track in the MKV has a numeric ID starting at 0. Assuming the filename of the MKV is “input.mkv”, you can get a list of IDs like this:
mkvmerge -i input.mkv
mkvmerge --identify input.mkv
The output will look something like this:
File 'input.mkv': container: Matroska Track ID 0: video (V_MPEG4/ISO/AVC) Track ID 1: audio (A_AC3)
Then you can use those IDs in the –compression options in the command line. Add “–compression ID:none” option for each ID. For example, if there are 2 IDs (0 and 1), you would do this:
mkvmerge --compression 0:none --compression 1:none --clusters-in-meta-seek -o output.mkv input.mkv
That's all there is to it. The output file, output.mkv (or whatever you named it) should be playable.
The –clusters-in-meta-seek option is not related to compression; it just helps make the file seekable on some players.