To create slow down or speed up motion using the fit to fill method in Blackbird, follow these steps:

Prepare the Timeline 

Make sure you have a clip already in the timeline that you want to apply the motion effect to. Set a duration range on the edit side to the desired length. For example, if you want the final clip length to be 8 seconds, mark an in point and set a duration range of 8 seconds on the edit side.

Set In and Out Points on Source

Now, go to the source viewer and set a mark in and mark out duration of 4 seconds. This will create a clip with a duration of 4 seconds.

Fit to Fill Motion Effect

With in and out marks set on both the source and edit sides, the fit to fill motion effect will be automatically applied when you edit the clip. Simply drag and drop the clip from the source viewer to the edit window.

Choose Insert or Overwrite

When you drag and drop the clip from the source viewer to the edit window, you will be prompted to choose between an insert or overwrite type of edit. Select the desired edit type, or map a keyboard shortcut for quicker access to either edit type.

Motion Effect on Timeline

After the edit is created, you will see the motion-affected clip on the timeline. In this example, it creates a slow-motion effect of 50 percent or half speed. The top line on the timeline represents the full duration of the edited clip, while the bottom line represents the source frames used to create the time-affected clip.

Adjusting Audio

If the audio tracks were enabled during the edit, the sound will also be slowed down by 50 percent. If this is not desired, make sure to disable the audio tracks when editing or delete them after the edit is made.

By using the fit to fill method, you can easily create slow-motion or fast-motion effects on your clips, and it saves you time by automatically applying the motion effect based on the marked durations.