It's the ending song of Nang Paya Prai. It's such a touching song. I think I remember a part where they have nang ek sing the song (mouth the song) the part where she had a hard time or something, but I'm not sure.
Hea's the link:
http://hk.youtube.com/watch?v=pCve2KZt7ec
Hea's the link:
http://hk.youtube.com/watch?v=pCve2KZt7ec