I know this is an old thread, but I have recently run into this same problem trying to author and burn an AVCHD. I used meGUI with a presets for AVCHD and a file size limit for DVD-9 the encoded MKV was around 7.9gb. After running the MKV through tsMuxer the resulting folders were .5% over the amount the disc would hold. Obviously I need to set the size limit to something else, but what? I like the quality meGUI produces (even though it takes forever to encode) and the simplicity of the program, thus I haven’t used multiAVCHD. Is there any way to estimate the final AVCHD folder file size after encoding to MKV?