M2TS it’s an high definition file type by Sony. Generally you can find it as an output of bluray discs ripping or a common format for hd camcorders.

In this small tutorial we see how it is possible to convert it into mkv (Matroska) “container” so it can be easily playable for many devices (tv, mutimedia players) and naturally without quality loss.

There are various commercial programs that allows do it easily in some simple steps, but there are also free alternatives.

First download tsMuxeR (it doesn’t require installation) and open the m2ts file

We can see the video and audio streams.
As output choose demux and press “start demuxing”.
At the end of the conversion a report is generated, an important value is the frame rate, note it (it allows to maintain the audio synced).
Inside the destination folder we can find the video stream (.264) and the audio streams (.dts or .ac3) and the subtitles if they are (.sup and .sub format).

Then download mkvtoolnix, for Windows is available both as installer and without installation.
Then open mkvmerge GUI and as input add the video and audio streams and subtitles if you have.

NOTE: The subtitles aren’t an accepted format from the extraction with tsMuxeR, you must use specific programs to convert them, for example SupRip and SubRip (or if you want use a more recent program you can use Subresync). They recognize the OCR of subtitles and allows the conversion in the .srt format (accepted by mkvmerge GUI).

Choose video track and on specific format option tabset the aspect ratio and the exact value of FPS, then convert it by pressing “start muxing”

At the end as result we have the mkv file!

NOTE: if the audio tracks muxed in the mkv are in DTS format it’s possible that not all devices can play it, so you must convert to AC3. To do that you can use free programs like PopCorn MKV Audio Converter or MKV2AC3. Both use the Matroska container as input. Naturally in the final file we then will find the DTS track + the new AC3 track.