PRG Mbox Studio Manual 3.8 - Manual (Page 135)

MBOX ® STUDIO USER MANUAL 127
Alpha Channel in Movies – the Animation and ProRes 4444 Codecs
It is often very useful to be able to add areas of transparency to a layer when using Mbox. This will make it possible to
see other layers behind, to create a "knockout" for IMAG, or to properly display a movie that uses green-screen
technology.
When creating content, there are several QuickTime codecs that allow an alpha channel (transparency information) to
be embedded in a movie. For the purposes of Mbox, the only useful codecs are Animation and ProRes 4444.
Encoding content using the Animation or ProRes 4444 codecs can result in movies having a very high or unplayable
bitrate. Take care to choose the appropriate quality setting to keep the movie's bitrate lower than ~150mbits/sec.
If a movie is created using the Animation or ProRes 4444 codec and played on Mbox, the preferred playback engine
will handle it. Mbox is able to use the alpha channel information in the movie and to display transparent areas as
transparent. However, unless the movie is quite small and/or has a low bit-rate (< 80mbits/sec), the movie may not
play very smoothly, and all other playback on the server may be affected to some extent.
Another way to create a movie with an alpha channel is to use the Animation codec conversion built into the Mbox File
Converter application. This application will convert the movie into a format that Mbox is better able to play while still
retaining the alpha channel information. When the movie is played in Mbox, the bit-rate is significantly lower – allowing
for better playback – and the transparent areas are still transparent.
Applications for Content Creation
There are many applications that can be used to create movie content for Mbox. They vary from the higher end
(Adobe After Effects®, Apple Final Cut®) to the lower end (QuickTime® Pro). All of them have their uses, but there are
some guidelines and caution to be observed:
+ Never create a movie with compressed headers or prepare a movie for internet streaming.
+ To modify both the framerate of a movie and trim the movie, do not use QuickTime Pro, as this will modify the
headers of the QuickTime file to the point where Mbox cannot play it. However, QuickTime Pro can be used to
convert a movie from one codec to another or to trim an existing movie. It is recommended that you perform more
complex tasks (changing the framerate) in such a way that the movie’s source elements are re-rendered into a
new file. This is especially critical if audio is involved.
Training Video: Mbox Media Server Training Video Chapter 20: Codes, Storage, and Media Types