add an extra audio track

[devdev]

hi i have tmpgenc mastering works 5. i have a video (two versions - one as an avi file and one as a mp4 file. )the sound of which was recorded on the left track only and i need to duplicate it to the right track too. any suggestions as to how i simply do this please? even if not in tmpgenc mastering works5?

[ProWo]

Can be done with clever Ffmpeg-GUI.
Load your mp4, click main, click encode audiostream, click go to the encoder.
If the audiostream is mono, set channels to stereo.
Click remap and insert 1 at both channels.
Then click encode.
If done, click multiplex, the new created audiostream is shown in green.
Select it and the videostream, deselect the old audiostream (the blue one) and click multiplex.
Done.

[devdev]

thank you very much