AE is best suited for creating visual effects shots or short sequences, editing is best suited to Premiere Pro. If you want to use Rotobrush to create a matte it will probably better if you do the compositing in AE. To find resources that will help you with the tasks just type Rotobrush into the Search Help field at the top right corner of AE and follow the links. You'll need some training to use rotobrush. Once you have a clean roto you can just build up your layers in AE and then render the result to a production format (not MPEG) or an image sequence and import that into PPro and edit the shot into your sequence.
You could also open the AE project in Premiere Pro and link to the comp with the roto work. If the shot is short and simple this may be a good option. It's called Dynamic Link. In my own projects I seldom use dynamic link unless the shot is extremely short and simple.
If you are brand new to AE you should start here: Basic Workflow
If you need other help with compositing then check back in with some specific questions and details of the shot you are trying to create.
If you want to composite in Premiere Pro then simply choose the Lossless with alpha preset from the Output Module in the render cue. This will give you a shot that you can use as an alpha matte in Premiere Pro or you can just use the shot and live with the transparency. I'm not sure what your shot is supposed to look like. If it were me I would do all the compositing in AE because you've got a lot better tools.
That's really not helpful. See my second paragraph.
- "once I create the selection using the roto brush..." so I'm not asking about how to use the brush per-se or how to get the clip into AE, or where to find the help button. But "just use the help" isn't really an answer anyway.
- "I'll complete the work in Premiere, so rather than learning how to do the entire project in AE" I don't want to learn all of AE top-to-bottom to do the project in there, but just help out one step for a project I'm already working on in Premiere.
In fact, it's amazing how non-specific the reply is compared to my question, and how non-informative it is in terms of generic information. Your third paragraph is describing what I wanted to avoid (rendering a full new copy in a low-loss format), and the first paragraph goes against the prerequisite I stated at the beginning of my post.
I should not even reply because you thought me rude and unhelpful when I gave you enough guidance to get you through the project with just a little effort on your part. Even so, here's some detailed help.
The search help field is the most useful part of AE for a new user. It's right here:
I've been using AE for more than 20 years and I use Search Help all the time to check on new approaches to old problems. I've been teaching AE for more than 18 years and Search Help is always included in the curriculum.
It would take me a couple of hours to write a thorough enough post to teach you how to use Rotobrush successfully, teach you how to render a video with transparency, and how to set up a track matte. AE is a program that will take you at least a half hour just to learn the interface.
If you type "rotobrush" in the search help field you will find this: Adobe - Search: rotobrush
The first link gives you the basics, the second gives you this: Use the Roto Brush | Adobe After Effects CC tutorials
The tutorial will set you up for creating your matte layer. Using the tool is much more than just clicking here and it would take too long to go through it here.
From there you can either render a video file with an alpha channel or you can render just the alpha channel and use either in Premiere Pro. Type
create matte' in the Search Help field and you'll get this: Adobe - Search: create matte
That brings up links on how alpha channels work, track mattes and even using a matte for use in other Premiere Pro.
If you do not understand rendering then type rendering in the search help field. Video is complicated, AE is way more complicated and you need to spend some time studying things to figure out what to do. You said you wanted to use Rotobrush to create a matte to use in AE. I told you how to use rotobrush in the first reply, you apparently didn't take the time to try and follow the links to learn how to use the tool. If you had followed the tutorial you would have seen how transparency was created and just a little research on rendering or even poking around in the output module, or using dynamic link in Premiere pro would have been very easy to discover.
Since you are apparently unwilling to do some research on your own here is a step by step:
- Open the clip you want to roto in AE or Premiere Pro and trim it to the length you plan to use because rotobrush takes time and you don't want to do more work than you need to
- In AE you can trim a clip by opening the video in the footage panel. You do that by double clicking the footage int he project panel. Now you set the in point using Ctrl/Cmnd + [ and you set the out point by using Ctrl/Cmnd + ]
- If you use Premiere Pro to trim your clip then right click the clip in the timeline and then create After Effects composition from selected.
- In AE, either drag your trimmed clip to an empty composition panel or select the trimmed clip in the Project Panel and choose File>New Composition From Selection or if you used Dynamic Link go to the timeline
- Select the clip in the timeline and double click the clip to bring up the Layer Panel
- In the layer panel use the Rotobrush tool to create your mask. This will take some time and you will not be successful unless you have looked at a tutorial. When the mask is complete and the edges refined save the work
- If you are using dynamic link go back to Premiere Pro and use the embedded comp as a track matte
- A better option, or if you are doing all the work in AE, drag the comp to the render cue and inside the render cue find the output module options and select Lossless With Alpha or Alpha only
- Open the output module and make sure that the alpha chanel is set to Straight
- Now render and import the rendered file into Premiere Pro.
If you have a good understanding of formats and codecs and rendering you can get a smaller file size than the default, but if you don't have a solid understanding of formats and channels then use the presets. The rendered file will be quite large but you'll just have to live with that because you should never use highly compressed mp4's or MPEG files in your production pipeline unless they are camera originals. MPEG formats were never intended for use in production as a digital intermediate. One more thing, if you render the file Premiere Pro will run faster and you will be able to work more efficiently than if you use Dynamic Link. Dynamic link is slow to render, uses only a small portion of the system resources, and must be re-rendered every time you make a change.
You stated that you did not want to render a large video file but that's the most efficient workflow. If you do not want to render you need to use Dynamic Link but be prepared for potential problems and longer render times.
So I hope this helps. Criticizing the volunteers for not giving you a complete step by step solution for free, especially when good advice is given, isn't a way to win friends and get a lot more free help on this or any other forum. If this step by step is not good enough for you then I don't know what else to do for you except to send you to a site where you can pay for some training.