Apple Motion 2 - Manual (Page 173)

Chapter 2 Creating and Managing Projects 173
Audio Files
You can import different audio file formats into your project, including but not limited
to: WAV, AIFF, .cdda, MP3, and AAC. Although Motion is not necessarily intended to be
a full-featured audio editing and mixing environment such as GarageBand, Soundtrack
Pro, or Logic, you can import music clips, dialogue, and sound effects to use in your
projects. If you import a QuickTime file with mono or stereo tracks of audio, the video
appears in the Timeline, while the audio appears in the Audio Editor.
More About Alpha Channels
Ordinary video clips and image files have three channels of information, one each for
the red, green, and blue channels. Many video and image file formats also support an
alpha channel, which contains additional information that defines areas of
transparency. An alpha channel is a grayscale channel, where white represents areas
of 100 percent opacity (solid), gray regions represent partially opaque areas, and
black represents 0 percent opacity (transparent).
When you import a QuickTime movie or an image file into your project, its alpha
channel is immediately recognized by Motion. The alpha channel is then used to
composite that object against any other objects that are behind it.
There are two different ways of embedding alpha channel information into files, and
Motion attempts to automatically determine which type of alpha channel a particular
object uses:
• Straight: Straight alpha channels are kept completely separate from the red, green,
and blue channels of an image. Media files using straight alpha channels appear
perfectly fine when used in a composition, but they may look odd when viewed in
another application. Translucent effects such as volumetric lighting, or lens flares in
a computer generated image, may appear distorted until the clip is used in a
composition.
• Premultiplied: This type of alpha channel is multiplied with the clip’s red, green,
and blue channels. As a result, objects with premultiplied alpha channels always
look correct, even with translucent lighting effects, because the entire image is
precomposited against a solid color. Most commonly, premultiplied alpha channels
are multiplied against black or white, but Motion can also resolve alpha channels
that have been premultiplied against other colors.
The only time it really matters which kind of alpha channel an object has is when
Motion doesn’t correctly determine it. If an object’s alpha channel has been set to
Straight in the Media tab when it’s really premultiplied, it may appear fringed with
the premultiplied color around its edges. If this happens, you can select the
problematic clip in the Media tab of the Project pane, and change its Alpha Type
parameter in the Media tab of the Inspector.
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