For what it's worth, I'm pretty sure I've found the location the witnesses were standing when the film was taken.
As I suspected, it's on the lowland section of the Mermaid's Pool to Edale route being walked; initially my memory vaguely recognised the landscape as being further east (I've walked that route more than once myself, although not for years) - but a bumble along the route via the magic of Google Earth put me right, and I believe the witnesses are standing on or near the road roughly here:
The small clump of trees top centre(ish) - directly below the highest point on the ridgeline - is the same one visible, along with a small ruin, top right of the video at the very beginning. You can't make out the structure in the capture above, but you can maybe just make it out if you go to Google Earth and zoom a little - and you can see it up close if you whizz up there using street view and drop on the Pennine Way, which passes right by it. (The apparent difference in perspective and distance will be explained by differences in lens type, focal length, and positioning of the camera - tree placement, tree and hedge boundary lines, and patterns of vegetation all correspond, the roughly horizontal band of vegetation half way up the very start of the video delineates the course of the River Noe, and the ruin is under a kilometre from the POV – which looks about right.)
Map view, with ruin/small clump marked for orientation:
Footage (and quality, veracity, etc thereof) aside, there are a couple of things worth bearing in mind when wondering if this is a place you might find an errant panther gulping down a dead sheep:
The general area is pretty close to the initial stage of the Pennine Way, this section of which is popular all the year round, even in quite savage conditions.
The subject is within 60 - 70 metres of metalled road (to the south and west – the Pennine Way footpath is to the north).
I’d also estimate it's within 100 metres of a relatively popular campsite – the corner of which overlooks the field in question.
It's within around 375 metres of the two closest farms. Suspending any disbelief for a moment, I get that a big cat might venture off the isolated high ground to grab a meal - but I find it hard to believe that a farmer would not notice, and be reporting, unusually predated sheep so close to home.
In my opinion, if a big cat was really that bold, that unconcerned by roads, human beings and human habitation, then I can’t help thinking that we’d be getting sightings every other day, not once in a blue moon.