Thanks for the replies, but there are two groups of seven notes and one group of four notes. It's the group of four notes that concerns me.
I agree that for each group of 7, it is clearly: d-u-d-u-d-u-d
And there is no way he's playing the whole thing with downstrokes, no matter how godlike he is
Down stroking on the very last note means he surely starts the first note of the four on an upstroke. It's either that or playing two downstrokes in a row, economy picking style, but that's a headache too!
I would play it:
d-u-d-u-d-u-(d)
d-u-d-u-d-u-(d)
d-u-d-(u)
The ones in brackets are the power chord at the end of each line (E5, E5, then F5 for the last one). All the other notes are open E string.
Rhythmically, you have:
triplet - triplet - quarter note
triplet - triplet - quarter note
triplet - quarter note
Each of the power chords at the end of each line/grouping are quarter notes, whereas everything else is triplets. So the quarter notes give you plenty of time to re-adjust your picking for the start of the next repeat regardless of how you end the line (upstroke or downstroke).
But it makes sense that each line would reset the picking pattern at the longer quarter note, so it always starts on a downstroke. And then each line/grouping is just straight alternate picked.