Congratulations, you have managed to describe an invisible elephant! Sorry, but this is useless. Show us your footage in action, screenshots of your AE comp and timeline with the relevant properties and keyframes revealed and so on.
used the "position/scale" options to make it appear as though it's flying through the air towards the viewer, but I'm encountering a problem during part of the 'movement' where the card appears to move choppily through the air;
more information would definitely help us figure out how to help you but first try this: instead of using position/scale and trying to match both to simulate a fly towards the viewer, toggle the 3d switch for the layer and use the Z position to control both of them together. you will get a realistic movement this way, and with less hassle.
I've rotoscoped a playing card and used the "position/scale" options to make it appear as though it's flying through the air towards the viewer,
Is the card moving? is this from a video?
The way you appear to be approaching the problem is going to be extremely difficult animate. Position/Scale is the most complicated way you could have chosen to animate something flying through the air. it sounds to me like you are very new to AE, motion graphics and animation..
My suggestion, get two stills of a playing card, one is the front of the card, the other is the back. A flat bed scanner is a good tool to use, but you could use your smart phone if that's all you have. You could also find a stock image of a playing card. There's a complete deck in vector format on Adobe Stock. Use Photoshop if necessary to remove the background so the image has an alpha channel.
Now add both the front and back of the card to your comp, make both layers 3D and move the back of the card to a z value of 1. Next rotate the back of the card 180º in Y. Make sure the Parent column is visible and then make the front layer the parent of the back and lock the back layer.
Now it's just a matter of animating position and rotation of the card as it flys toward the camera. If there is camera movement you may want to either camera track or motion track the shot so you can keep things looking real. You may also want to add an ambient light and a directional light to the scene to match the lighting in the scene. The last step, after you have successfully animated the card is to turn on motion blur for both card layers and the comp.
I hope these suggestions help. If I'm completely off track please include a detailed description of the shot you are trying to create and if possible a screenshot or the video you are using as the background.
I'm not new per se, but I haven't done a lot of motion-graphics animation, and most of what I've done with AE is very simple. So, yes, I guess I might as well come at this as a beginner your suggestions are very helpful though, I'm going to see what I can do with them and report back later. Thank you!
Roei, thank you for the suggestion! I'll see what I can do with all of this new information.
One problem with using just front and back pictures of a card is that it will be infinitely thin, with no depth. Maybe a very thin 3d box could be used to give it a bit of depth.
Rotoscoping a real playing card (plus adding extra movement to it, eg. in 3D space like has been sugested) might also give good results. For checking errors in movement maybe also check the handles on any keyframes that seem wrong in the graph editor.
Cards are pretty thin. The card will be 2 pixels thick. You can add more layers and make the card 4, 5, or six pixels thick and it will render way faster than using Ray-traced or C4D rendering and extruding.
This worked, and it looks much smoother than my previous attempts. Thank you all for your input, and especially for yours, Rick!