A support question came up today about how does one configure Studio Artist to pass through a source movie's embedded alpha channel to a Studio Artist rendered output movie. So the rendered output movie file would have the exact same embedded alpha channel as the source movie file being processed.
This is actually very straight forward to do. There are 2 main things to be aware of.
1. First, you need to make sure you are using an output movie compression codec that actually supports alpha channels. Not all of them do. The Animation codec does, so that's one option. If you are working with ProRes, then you need to make sure you use the ProRes 4444 codec. It's currently the only ProRes codec that supports embedded alpha channels.
It's not enough to just pick a codec that supports alpha output. You need to make sure it's controls are configured to actually turn on alpha support. This usually involves selecting a millions of colors+ option. If you just choose millions of colors (without a +), then you will not get an embedded alpha channel, even though the codec type supports one. The + stands for adding an alpha channel to the normal RGB color channels.
2. Second, you need to configure the Embedded Alpha movie preference setting so that it is set to Source Alpha. Embedded Alpha is the name of a movie preference option. It is a popup in the movie tab in the main Studio Artist preference dialog.
There are a number of different Embedded Alpha movie preference popup options (as shown below).
Full On is the default setting. This would insure that an embedded alpha channel was set to full on if a movie was being rendered with a codec setting that supported embedded alpha channel output.
The Source Alpha option just passes through the source movie's embedded alpha channel to the rendered out movie's embedded alpha channel. So if this is what you want to do, setting the Embedded Alpha movie preferences popup to Source Alpha is all you need to do to achieve this.
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