It's really a bad decision to telecast old songs in stretched format. I think watching videos in proper look would be better rather in full of a tv screen.
I don't know what's going on with sun music. Today I also noticed the same. (They're telecasting Latest songs in stretched mode. My opinion, In case of ads, it's completely their laziness on afford HD videos, but for old songs they could broadcast in letter-box format with some blurred background or something instead of black screen in the backdrop.
Guys, I think they are trying multiple options. So let us wait for few days for them to settle down with some option. Till yesterday, HD songs were in 16:9 ratio only. Not checked now. Only 4:3 songs and advs were stretching. For me it was good instead of seeing black bars on left and right side.