b) hmm;
c) but then if there is only one master control, they'll just have one volume control to mess with, right?;
d) I don't buy that & here's why: are you really going to be listening to other tunes in the background while you're listening to a TED talk? For case 2, you can pause/mute the video (all I'm referring to is the volume control slider in embeds;
e) I agree 100% not to make any assumptions about potentially billions of users but with a main audio slider for their device I don't force them to mess with two volume sliders.
Besides desktops, I think about tablets/mobile phones, how often do you tweak the volume of the embed itself and not the audio for the entire device?
Bridge: You are spot-on that it should be a crime for auto-start on audio (I feel like a few jerks who tried the auto-playing "Congratulations, you just won a free iPod blah blah" will be eliminated quickly) but I think we can kill off the volume sliders (assuming no auto-start audio, easy pause/mute)
I'm still trying to see if there is a bullet-proof use case out there where it is essential to have a volume slider on an embedded item itself.