I'm editing a music video on premiere pro CC, footage consists of 1080p footage from a canon 5D mark II, 4k footage from a phantom 3 and an inspire 1 drone, and 720p from a canon 5D mark III, it was recorded in 720p so we could record it at 60 FPS, to get smooth slow motion. The group was lipsyncing the song being played back at 200% speed, so that when we slowed it down to 50% it looked really smooth while still looking like they were singing, so far looks great. The bulk of best footage bits are in 720p.
Problem is, we just found out that one of the outlets that's going to play the videoclip only accepts 1080i footage, they hadn't send the specs before so we didn't know that bit of information.
So we're facing two posibilities... either we change the timeline to 1080i and scale up the 720p footage (what we want, if possible), or just bite the bullet and reshoot all the 720p images we used in 1080p and use twixtor for the slow motion.
So, that's my question... what would you suggest?... is the quality loss when going from 720p to 1080i too big?... if it can be done while preserving image quality, what would be the best workflow to achieve it?.
720p scales to 1080 pretty well. Now, there's no way you can convert progressive to interlaced, but really, if you put 720p into a 1080i timeline, and deliver that, it'll be 1080i. Both fields will just happen to be the same. This might be something you want to communicate with the client, that you have progressive footage, but can still deliver a 1080i master.
ONLY accepting footage SHOT 1080i seems very odd. But only taking a 1080i master, that's pretty normal, actually.
I would convert 720p to 1080p in Premiere Pro using a CUDA GPU card. This should give you some very good result.
Obviously not seeing your original footage, it will be hard for us to tell if this is "good enough" or "not acceptable". I would do a test and see if it is acceptable to you watching on a reference monitor.
I would then finish your program in 1080p and make a progressive master. Only then I would make a 1080i version. I usually like to use After Effects for that last part with more control in the output. Going from 1080p to 1080i is actually the best 1080i you can get;-)