Seriously Need Some Help With Tracking!

Discussion in 'Digital Video' started by acearchie, Dec 4, 2012.

  1. acearchie macrumors 68040


    Jan 15, 2006
    Hi guys,

    I have to track a one take scene so as to replace the screen behind the actors.

    Here is the album of screen grabs.

    Can someone suggest the best way to tackle this? As you can see no point remains clear for the whole take so what would you recommend?

  2. jonjiv macrumors newbie

    May 29, 2012
    Adobe After Effects can track the 4 corners of the screen, but only when all 4 are visible. Since part of the screen is almost always obscured, you're unfortunately going to have to guess where the hidden corners are in the rest of the shot, frame by frame, working backwards or forwards from the last moment all 4 corners were visible. You don't necessarily have to keyframe every single frame since After Effects can interpolate the movement between two of your keyframes, but if the camera is moving a lot, you'll be pretty close to tweaking every single frame anyway.

    I would set up my layers like this.

    -Chroma-keyed shot on top with a rough mask around the screen area (in case the chroma key deletes the trees out the window.)
    -Tracked screen in the middle with motion blur enabled.
    -Original shot on the bottom.
  3. Siderz macrumors 6502a

    Nov 10, 2012
    What version of After Effects do you have?

    Because it normally comes with Mocha, which is an excellent tracking tool, and may help in a situation like this.

    I wouldn't say that this video is that good, but it might get you on your feet with Mocha and you could possibly watch some other tutorials -
  4. acearchie thread starter macrumors 68040


    Jan 15, 2006
    Turns out traditional tracking won't work as the corner points get blocked by the actors far too often and guessing the points is a night mare.

    I have instead opted for learning 3d camera tracking and laying the screen replacement in 3d space.

    It's taken most of the day to get up to scratch with tracking, how it works and how to implement it but I was able to give it a quick whirl before calling it a day.

    Hopefully being fresh tomorrow I should be able to tackle the remaining 2mins30secs of the video! :eek:
  5. Siderz macrumors 6502a

    Nov 10, 2012
    I think you've done quite a good job with that.

    I was going to suggest 3D tracking, but that's often quite expensive/takes a bit of practice to master.

    One question though, how did you managed to embed a YouTube video? I was trying to embed the video I posted, and searched for it, people say that embedding videos on these forums is frowned upon and not possible.
  6. acearchie thread starter macrumors 68040


    Jan 15, 2006
    I have taken the 3d tracking route but all within AE CS6.

    To embed a YT video use the tag [ Youtube ] (without the spaces) then copy in the letters after watch? in the url, for instance for mine it's "ZlzRqg9afEc" and then close with the tag [ /youtube ].

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