First of all, I'll implore you to start with the documentation and tutorials linked to from here for Roto Brush. I've seen an unfortunate amount of misleading garbage online that pretends to teach this feature.
To answer your question about whether you can use the Roto Brush tool to replace a background: of course. Any feature that allows you to create alpha channel (transparency) information for one layer can enable this. You just make parts of a layer transparent and then put the new background layer underneath. This is basic compositing. (See this page.)
But---and this is crucial---using the Roto Brush tool isn't as precise as manual rotoscoping can be. If you want perfect edges such that no one can tell that the new background is not the original background, you'll probably have to do some touch-up with manual rotoscoping. It's hard, tedious work, no matter what software you use.
This is why people shoot on greenscreen---so that they don't need to use features like this that take so much time and patience. It's also why the credits at the end of a movie contain often hundreds of people with the title "roto artist". It's incredibly labor-intensive.
ok i got it going =).... i was scratching my head yesterday trying to figure it out why it wasnt showing any changes, but all along i was looking at the layer window, and forgot that that wasn't the comp window. so when i switched back it looked how it was supposed to (or as close as i'm willing to get it, for me just messing around with this, and not being payed. lol)
hmmmm.... ok since this is my first time messing with this... i may be doing it all wrong. my source footage is just regular 480i dv-avi, baout 7m50s long. i imported it into the comp, broke it up into 9 layers, the first and last layer being the introduction to the speaker with heavy movement, and then the middle 7 segments being 1 minute each of him just at a podium. i actually spent time keying the first and last layer/segment. but all the middle segments were of little motion so i just set 1 rotokeyframe in the dead middle of each layer, and dragged out the left and right side of the keyfram work are to cover the whole 1 min segment each. i did that with all 1 minute segment layers, and the first and last segment probabably has 6 keyframes each.
it is saying to complete this task will be 65 hrs long. is this right? or should i be setting this up differently?
my pc set-up is win7 running adobe prod prem cs5, there is no dynamic link being used, so everything is strictly housed within after effects for this comp. i'm running a 3ghz quad core AMD, with 8gb of ram, and i have all ram allocated to AE. i have adobe and windows, as well as .ae files on one 1tb sata HDD, and the source avi file as well as the export avi on a seperate 1tb sata drive. it says AE is only using 28% of available ram for some reason. my set up should more than handle 480i dv footage, yes? i started the export at 3 1/2 hrs ago and it has done only 24 seconds worth of footage. so whats the deal? whenever i was setting keyframes AE kept barking at me that my comp did not match the footage, it said the comp was 29.9 fps, but the footage was 59.9 fps (which is completely wrong, and i have no idea why it said that) i change dit anyway to get that error to go away, would that have anything to do with this?
eta: i dont have a MPE graphics card, but i mainly work with DV footage, so have not had a need (yet...)
I must be missing something. There's no way that a properly setup DV sized project only 7 minutes long should take 65 hours to render unless it has a boatload of effects applied to a boatload of layers.
Are you using RotoBrush? If so then did you go over the instructions for using it?
You must start at the in-point and work forward. Any time you go back and make a change RotoBrush starts from the change and renders new mask frames. Once you have the entire clip analyzed and the little green line at the bottom of the Footage layer goes all the way across, then you must press Freeze and let RotoBrush render the masks for the clip.
If you don't render the masks and freeze then RotoBrush will not only take forever to render, but the results will not be anything like you expect. Simply dropping a keyframe in the middle of a nearly static clip won't work at all because only the frames after the keyframe will have any chance of being analyzed. Rotobrush works very well and renders quickly if you start at the front rendering the mask and then freeze. If you don't you're just wasting your time.
If the middle segments of your project are nearly static then it may be faster to simply use a regular mask drawn with the pen tool (g). I wouldn't know unless I saw the clip.
no i have no other effects, other than rotobrush... i'm just seeing how it works and how much work is involved... not trying to do anything of any epicness
Rick Gerard wrote:
If you don't render the masks and freeze then RotoBrush will not only take forever to render, but the results will not be anything like you expect.
man, i'm really embarrasing myself with this. lol.
yeah i did that ^^^ for the first segment, but forgot to do it for the others. the first layer just goes "bam!" and its done.... then it just hits a wall of nothing. but i forgot to analyze and then freeze for the remainder layers. ok i'm on the right track now. thanks again