Handbrake

Install Handbrake – The open source video transcoder

Only use this software if the original MTS-videofiles are too big for your computer to handle in Subtitle Edit.

It is preferrable to first join and convert the MTS-videofiles with Format Factory.

If the file is still too big you may use HandBrake or better: change the settings in Format Factory to a lower quality.

Surf to:

https://handbrake.fr/

You may lower the MTS video quality to MPEG-4 or even MPEG-2