Adobe After Effects - Can I have multiple simultaneously active cameras in a comp?

Author

Can I have multiple simultaneously active cameras in a comp?

Mark_Silvestri@adobeforums.com

2006-12-06, 8:14 pm

I'm using a camera to animate lifting musical notes from a still photo of sheet music ... it works very well. The musical notes are 3D while the sheet music remains 2D. However, I would like to create the effect of several notes lifting from the sheet at
the same time. To do this using my current approach requires me to have multiple active cameras at the same time. Is this possible in After Effects 7 Pro?

I have tried precomposing each musical note with its own camera then using those precomps in my main comp, but AE just seems to use the camera within the precomp that is positioned in the topmost layer of my main comp. Any ideas?

silversurfer@adobeforums.com

2006-12-06, 8:14 pm

You can pre-render each note with it's camera with a Straight Alpha Channel and bring them back into the composite.

- Joey

Aaron_Cobb@adobeforums.com

2006-12-06, 8:14 pm

AE can only have one active camera on a given frame of a given comp. It is, as you've noticed, the topmost "live" camera in the timeline. You can switch cameras on or off by toggling the video switch or by setting the in and out points of the camera layer
s. If you want to have images within the comp that obey different cameras in the same frame, then nested comps are the way to go.

Without seeing your project, it is hard to diagnose the problem, but the fact that you have nested your comps and are finding that the nested comps' layers are being rendered according to the current comp's camera suggests one of two things: either you ha
ve collapsed transformations on the nested comp, in which case the camera inside that comp is simply ignored, or you have enabled the 3D switch on the nested comp, in which case the nested comp is being rendered correctly, but the result is then being pla
ced as a 3D image in front of the current comp's camera.

I do wonder, however, why you need multiple cameras in the first place. If you simply want the notes to lift off the sheet of music, this can be done by animating the notes (or groups of notes) individually in front of one camera. Is it possible you are m
aking this far more complicated than it needs to be?

Mark_Silvestri@adobeforums.com

2006-12-06, 8:14 pm

Thanks, silversurfer. This simple approach worked just fine for my current need.

Aaron, thanks, as always, for the thorough response. To answer your question, yes, I very well could be making this more complicated than it needs to be. Here is a quick description of how I "lift" the notes. Any feedback is appreciated.

1. Take a still photo of an artistically-positioned page of music within a music book. In my case, the book is opened to the target page with the book lying flat and the page somewhat curving to lie flat due to its attachement at the binding. The still ca
mera I used is positioned to the bottom left of the book and just above the table holding the book. The only reason I provide all this detail is to show that the notes are oriented in a non-trivial manner, which is why I decided on using an AE camera to h
andle all this 3D-ness for me.
2. Create simple head-on drawings (in Illustrator) of the musical notes I intend to lift (eighth, sixteenth, inverted eighth, etc.) and import one to AE.
3. Pair an AE camera to a null and orient the null to roughly mimic the X, Y, Z rotation of the original still camera. With the null and my note at the center of the comp, add a little point-of-interest and Z-axis adjustment on the camera itself and I hav
e the starting position of the note on the original music page.
4. With a few additional keyframes on the null position, I can easily get the note to very naturally lift off the page and follow a pleasing path to orient itself in a head-on manner so I can use the face of the note to show some video as it moves thru sp
ace.

My problem occurred when I tried to overlap and stagger these individual note pre-comps - only the topmost camera was live, even though it was contained in a pre-comp (no collapsed transformations in the main comp).

Are there easier ways to skin this cat?

Rick_Gerard@adobeforums.com

2006-12-06, 8:14 pm

I think I understand what you're doing. First of all, it would probably be simpler to just use 1 camera and orient each 3D note to match the page. There's really no need to pre-compose at this point. You can then either manually fly the notes off the page
, or tie all the notes to a single null and adjust timing with an expression. This solution requires a fairly good, but not expert understanding of expressions.

The other option is to set up everything the way you're doing except don't move the camera from it's original position or shift the point of interest. Just move the note / null into position and if necessary adjust the scale value of the note.

The last option would be to build up a comp from your original photo as a 2D layer, then import each of your 3D pre-comps with flying notes but make sure that the background photo is turned off so you're bringing in only the notes. There would then be no
need to add a camera to the final comp.

If none of these solutions work for you just post your problem comp with or without footage and I'll be happy to take a look.

Aaron_Cobb@adobeforums.com

2006-12-06, 8:14 pm

If I understand you correctly, the easiest way to do this would be to use one camera and to animated the notes as they lift off the page. But without seeing the project it's hard to say for certain.

As for your problem of the camera in a nested comp overriding the current comp's camera, I don't think I understand what you are describing. Any interpretation I can come up with runs contrary to the way AE operates. There aren't any circumstances under w
hich a camera in a nested comp gets used to render the image in the main comp. It will render the nested comp, and that result will then get placed as a layer in the main comp.

Rick_Gerard@adobeforums.com

2006-12-06, 8:14 pm

There aren't any circumstances under which a camera in a nested comp gets
used to render the image in the main comp. It will render the nested comp,
and that result will then get placed as a layer in the main comp.

I'm not sure Aron said what he meant here. If you do not collapse transformations any cameras used in nested comps will be used. It's only when you collapse transformations that the main comp camera is used to render the 3D items in the pre-comp. In simpl
e terms, collapse transformations = use camera in main comp, collapse transformations off = use cameras in nested comps.

This is why my last option suggested above may be the solution to your problem.

Aaron_Cobb@adobeforums.com

2006-12-06, 8:14 pm

I didn't express myself clearly. What I meant by that passage is that, assuming no collapsing of transformations, the nested comp's camera will render the nested comp's image, and that result will be used in the main comp as a layer to be rendered by the
main comp's camera, but the camera in the nested comp will never be used to render final image of the main comp.

Mark_Silvestri@adobeforums.com

2006-12-06, 8:14 pm

Thank you, gentlemen.

After carefully reading thru your posts and retrying things, I am able to achieve what I originally intended - precompose each note with its own camera, nest each precomp in my main comp, and overlap precomps while maintaining the camera transformations i
n each precomp. I accomplished this using the approach that Rick described (and Aaron confirmed) as his "last option" - my original intended approach. Not sure why this was not working for me, earlier. Perhaps I had a camera in my main comp that was foili
ng things, but I didn't think so.

Now, the only thing causing me a problem is maintaining best quality footage for my video (scaled down and masked by a track matte onto my note body) as I slowly move the camera (Z-axis) past the note. However, for proper tracking, I will capture this que
stion in another post.

Thanks, again.