#CreativeFriday – MotionTracking objects in videos using Premiere Pro CC & After Affects CC

Once you are signed up for the Adobe Creative Cloud, wanting the next app goes away, as they are all there, all ready for you to learn and use. In this tutorial, we are going to head over into the video solutions with Premiere Pro CC and After Effects CC (make sure you have both applications downloaded from your Creative Cloud desktop app) , and look at how to accomplish tracking an object in a sequence to cover it up. On a recent trip I shot a bit of footage that I intend to use in a 2 minute video. However, looking back at the recording, I realised that I needed to mask/blur something out, in this case a number plate of a small Tuk-Tuk  (if you watch the video below you will see a Tuk-Tuk come in from the right hand side, then disappear into the frame and will be obscured by another vehicle).

 

Open Premiere Pro and navigate to the media browser, find your footage and then right click it to import into the project’s media bin.
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Once the clip has been successfully imported into the Project’s media bin you will be able to place it onto the time line. To do this, right click on the clip and select “New Sequence from Clip”, this action will create a new sequence as well as placing the entity onto the time line.
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First thing to do with any media in Premiere Pro when wanting to make a cut, is to select the piece of footage from within it that you would like to use in your final piece. Doing this will not only enrich your final film and control the pace, but also save you a lot of time when modifying the track and adding any special effects. Premiere Pro and After Effects both look at individual frames of content when analysing them for post production. In any one video there will be a series of frames, frames are effectively single images strung together and played in a sequence. Typically there will be 24, 25 or maybe even 60 frames in each second of time, depending on how the footage was shot, regardless there are potentially a lot of frames to analyse for the special effect that you may be applying. From a performance point of view, the less frames there are to process, the less time it will take to render and complete.
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The first thing to do when working with footage is to cut it down to size (this particular clip will be part of a longer piece of footage and is a cut away scene (cut away’s are traditionally used to break up the main line action). There are many ways to edit and cut this clip, for this cut, I will use the play head (highlighted in blue) to select the “In” or “Start” point on the time line (i.e. where the clip needs to start from).  The start point that i need is when the Tuk Tuk that i want to follow comes into frame, the finish point for the clip or the “Out” or “End” point is when the Tuk Tuk is about to leave the frame or something else obscures is.
Position the start frame, by moving the play head to the desired start point, once you have found this (don’t forget you can also use the source monitor to do this as well. Once the start frame has been located, press CMD+K, this will cut the clip at the play head.
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If you hover over the section of the clip that is not wanted, right click on it and select Ripple Delete (Ripple Delete will remove any spaces/gaps from the clip). You may need to zoom into the time line to perform the delete, especially if it’s only a few frames, to do this you can drag out/in the horizontal scroll bars at the base of the time line panel. Next find the “Out” or “End” point, press CTRL+K, then right click and perform the Ripple Delete on the unwanted section end of the clip. One thing to note, Premiere Pro and After Effects are non destructive editors and will not do anything to the media you are working in. The clip in the time line is just a reference to the main video, you are able to bring back these deleted sections in the future if you make a mistake here.
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You should be left with the useable section of the clip.
Once you have the section of the clip that contains the piece of footage that you need, right click it and select “Replace with After effects Composition”. This menu option uses the Adobe Dynamic Link engine to link both products together and create a seamless workflow. Premiere Pro will send the piece of footage to the After Effects timeline and in real time will reflect in Premiere anything that is done in After Effects without having to render the footage/export or any other post render process. This also means that you are able to hot swap between both solutions to fine tune your changes.
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Now switch over to After Effects.
Once inside After Effects, the first thing you may need to do is save the project file (choose a safe place and save), then you should see a screen similar to below, with the clip in the time line.
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The objective of the exercise is to track the number plate from when it comes into the frame to when it exits, so we need to create a couple of items in After effects to hold relevant data points. The first thing we need to create it a NULL object (we will use this object to hold the tracking and motion data that After Effects will create).
Select the menu item Layer / Null Object, then you may want to rename it
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You will see the Null object in the time line, you can right click on it to open the menu and choose rename.
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We then need to create a Solid object which will be used to cover the number plate (this will be just like a solid colour layer in Photoshop). It maybe (as in this case) appropriate to blend the colour of the Solid in with the item that we are tracking. To do this you will need to drag and position the play head to a frame in the clip that contains the object that you are wanting AE to track, you are then able to derive the Solid colour from this using the eye dropper tool (you can also manually select the colour in the Solid creation box as well).
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You may want to rename this Solid in the first field (Name), to make it easier to find later in this editing process.
Clicking on the “Make Comp Size” will make the solid the same size as the canvas of the frame, then you can select a colour of the solid. In this case I want it to be a similar colour to the number plate I am trying to cover. Click on the eye dropper (highlighted Red below), select the colour from the frame, of course you can also click on the colour box and manually select the colour for the solid using the colour picker.
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You will see in the timeline now you have multiple layers (The video is the bottom layer, the middle layer (NULL) will hold the motion data and the top layer is the Solid).
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We are now going to create the tracking motion data. Firstly see if the Tracker window is open, if not, select Window / Tracker. The window will appear or will already be in the bottom right hand corner of the screen (when using the standard panel configuration).
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For the motion tracker to work properly you need to make sure that the “Track Motion” (Red) has been clicked (this tell’s After Effects what you about to do). Then the Motion Source (Yellow) entry needs to be the clip that you are about to use at the source footage. The area highlighted Green tells After Effects the type of algorithm to run, in this case we are going to select position (as it is the position of the object in the frame that we are going to track).
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Once the “Track Motion” in combination with the “Position” options have been clicked, After Effects will show two squares on the clip. I have already moved the clip to the start position the frame for where the the number plate first appears (this isn’t the first frame in the sequence (will cover this later), as the Tuk Tuk appears slightly earlier).
The Tracking point tells After Effects what to look for in the frame, in this case the number plate (notice that number plate has enough contrast for it to be found (this will make it easier for After Effects to track it though subsequent frames)). The inner square is the area that we are looking for across the next frames, and the larger square is the area in which to look for the tracked object. The combination below will give After Effects enough information be able to track the number plate, even if it moves slightly out of the inner box.
N.B. Take into consideration, that the larger the outer box, the more work that After Effects is going to have to do, therefore will take longer time to analyse the area and ultimately take a longer time to process.
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Once you have selected the area that After Effects is to look for, press the play button in the Tracker panel, this will move the frames on one by one, and will try to automatically find the object.If After Effects finds the object, it will place a blue track mark on the frame then we are able to modify the position if required and then store the data in the Null object that we created earlier.
As you can see in the image below After Effects has created each track point and highlight them in Blue. If any of the track points are in the wrong place (you can test this by moving the play head forward and backward). You can then zoom into the image to see more detail (use CMD and + and CMD and – to zoom in/out). You can then grab individual points and move to the exact location of the tracked object.
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The Blue icons are telling you that the motion points are temporary and have not been saved.  Click on the “Edit Target” on the Tracker panel, and choose the Null Data object and not the Solid. Then to apply the changes, click the “Apply” button in the Tracker panel.
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When you click the “Apply” button, After Effects will ask you to confirm the the positions to store (x and y dimensions are fine for this motion tracking piece).
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If you double click on the Solid object layer, and you will be able to work with this layer (as below). When the Solid was created we made it the same size as the comp, now we need to resize it so that it matches the object it is going to start tracking. To do this, select the direct selection tool (Red) and grab a red handle (Yellow) and re-size the Solid to the same size as the object we are going to (don’t worry about the resize of the object due to it’s size when the tracked object moves around). You are able to move the solid by selecting the middle point with the direct selection tool and drag it around and out of the canvas.
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Move the Solid over the Tracking point.
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The next step is to attach the Solid to the track data, this will allow After Effects to move the solid in line with the tracking data. The central point of the solid will be used as a reference point. Click on the parent of the solid and select the Null object.
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To test the tracking, you can move the play head backwards and forwards and you should see the solid move with the tracking point.
Additional Steps
In the above example the number plate will decrease in size at a constant’ish rate as the Tuk Tuk moves away from the camera (Tuk Tuk’s tend to drift sideway’s quite a bit as well). The solid that we are using will need to decrease in size as the number plate moves away and into the scene.
This problem is easy to solve in After Effects. Open the Solid layer effects by using the arrow to the left of it’s name, you will then see the list of options that you can use to create motion tweens & key frames. To enable After Effects to reduce the size/scale of the solid, position the play head the start frame (in this case it will be when the number plate comes into view), as opposed to the first frame of the clip (in this example). To create an initial key frame, make sure the play head is in the correct position, click the clock icon (Green), this will create a new key frame (Yellow & Pink). The Yellow marking on the key frame will mark where in the time line where the key frame starts (or when something changes) .The pink marker will show that we are parked on a key frame, the arrows either side of this marker, will move the playhead to the next key frame, if there is one available.
To create the reduced size Solid as well as the animation of Solid over time, move the play head to a future point in the video where the number plate is smaller than the Solid, then create a new key frame by changing the size/scale of the Solid (don’t click the timer, is this will remove the key frames). This operation will instruct After Effects to create a motion tween from the last keyframe to this key frame (tween is used to represent the frames that will be created be-tween the 2 key frames).
Repeat the above until the number plate has stopped changing size or is no longer in view.
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Notice the key frames in the following image on the scale configuration.
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When we play this video from start to finish there is a problem. Because we started the Solid movement at a point that was different to the first frame of the clip, the Solid will stay on the left hand side of the screen, until the motion data frames are reached, then, once the motion is found the Solid will start to move. This looks odd , so we will need to move the Solid off the screen until it is time for it to appear.
The simplest way to do this, is to make a keyframe of the Solid at the start of the Motion tracking by clicking the timer on the Position option, then find a position in the video just before the motion tracking starts. In this example it is when the Tuk Tuk is on the screen and the number plate is just off the screen. When this has been located grab the Solid using the direct selection tool and move the solid out of the frame. This will create a new keyframe for the Solid on the timeline and subsequently won’t show the Solid until the Motion Tracking frames start.
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Finally save the composition.
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Keep After Effects open and switch over to Premiere Pro (you may want to fine tune the After Effects comp). You will see the clip is now pink in the time line of Premiere Pro (Red).
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To test the video, reposition the play head in Premiere Pro and press play or the space bar.
Additional modifications to the Solid.
Once the Solid layer has been created and attached to the Motion Track points you can then modify how the layer works with the underlying pixels. In the following screen shots you can see how you can add an opacity element to the Solid, then modify the opacity by using the keyframes in the same way as we did with the scale/size.
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You may also want to modify the amount of blur with the underlying pixels, using something like the “On the Time / Pixel Motion Blur option” or the “Effect / Blur & Sharpen / Gaussian Blur”.

The following screen shot shows the Gaussian Blur and Opacity options.

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One Response to #CreativeFriday – MotionTracking objects in videos using Premiere Pro CC & After Affects CC

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