Yes, to remove the background you can either put a mask directly on the footage layer or put in on a solid layer on top your footage layer and use this layer as track matte.
For the basics of masking see:
For efficient rotoscoping, I also highly recommend the following tutorials by me
Thanks Mathias. Well I tried to use the method I mentioned in my question but the result was horrible as the crowd I want to keep in the foreground is moving from left to right very fast. The mask followed the track point ok but did not remain over the crowd lagging instead!
I tried then to roto brush the crowd but actually the people run so fast that some of the edges are so blurred that you cant make the difference with the background and the result is very poor.
I think I'll have first to find a better clip to do the trick. My problem is to find it as I need people dressed as Romans of 79 Ad during the Vesuvius eruption and seen from their back to blend correctly in my shot! They should be running from the foreground of the picture into the street.
What I did not use was the AE Track Mask animation option, I suppose this is what the first video tut calls the AE Mask Tracker. As I'm not in a hurry I'll wait for my return from Pompeii on June 10th and buy the MaskTracker+ tool If you consider this a good buy and worth the investment for an amateur video "editor" (I'm not a professional and this is just a hobby!).
If you have lots of motion blur, I recommend to use mocha in combination with the Refine Edge tool in AE (this is what I show in the second half of the tutorial about the Refine Edge Tool.
It may also pay off to have separate masks for each person in the crowd or even each body part that moves independently. It seems to be a lot of extra work, but it is actually faster, since the tweening and the tracking are more accurate and the masks only need to be accurate in the regions where they don't overlap.This is what I do in this tutorial (see chapters 4 and 5) to rotoscope the hand:
Concerning the question whether MaskTracker+ is worth to buy. Well, I developed the tool and I know that it is very useful for rotoscoping/tracking tasks. But mocha is more robust. So if you do tracking/roto frequently, I recommend my Tracking Bundle which contains both MaskTracker+ and MochaImport+. With MaskTracker+ you can do everything inside of AE, and when the MaskTracker gives no good results, you can still switch to mocha and do the same with MochaImport+.
Thanks again Mathias for this very useful infos.
I'll try the multiple masks idea and check out your other tutorials carefully. I have Mocha+ (I took advantage of the NAB discount and it gives free upgrade to the new version to come this fall). I'll check also your other products on the site.
For the moment I finalizing details of my V3 version of the prelude of my little movie. A fantasy film on Pompeii and Herculaneum sites inspired by Théophile Gautier's novel "Arria Marcella". A very ambitious project for an amateur including use Video copilot Element 3D and DAZ Studio for the main character of a Roman coming back to life to serve as a guide of the ruins which comes back to their original splendor when the guide shows them to the visitor. Here is my shot of the Temple of Jupiter in the middle of pyroclastic surge. If you have any suggestion to make it better don't hesitate to tell me. I'm here to learn. The sound is not yet corrected and normalized here . I do that in the end.
Mocha Plus is a product by Imagineer Systems - a version of mocha that contains more features than the one that is bundled with AE.
MochaImport+ is a product by mamoworld (my company) that makes using tracking data from mocha (no matter from which version) in AE easier and more powerful.
Concerning your clip: One thing you could improve is that the fire in the forground should cause some "reaction" of the stones directly behind them. The fire is like a light and it should illuminate the stones behind it. Also it looks like the bottom border of the fire clip shows the silhouette of some stones or so. Maybe you can cover this with some stones or other foreground elements.
OK Thanks, I'll check that as I've decided to make two shots from the clip with a different angle. After inserting it in my full video timeline, I find it too long although I have to keep the whole length because of the accompanying music (Holst's Planet's suite Mars the warrior. I found a very good creative commons version by the US air Force Band very well conducted and very players of such a difficult score.)
Yes I know the AE version offered of Mocha. I thought it worth getting the + edition upgrade because of the important discount Imagineer offered during the NAB conference.
Yes, Mocha Plus is really useful - in particular because of Premiere Pro support and the camera solver.