Harmy said:

That would be great! Thanks. If it made things easier, I could always demux the *.264 file from the m2ts prior to the conversion.

How does one define the codec, which is to be used for the lossless compression? If that is part of the script (which I expect it has to be) I'd like to use "UtVideo YUV420 BT.709 (ULH0) VCM".

Demuxing won't be necessary.

The compression is handled by the rendering application which, in this case, is FFmpeg. Unfortunately, FFmpeg can't do UtVideo encoding at the moment.

Rendering with VirtualDub might be better in this case.