Alpha Channel In Movies; Prores 4444 And Hap Alpha Codecs; Still Images; Audio - PRG MBOX User Manual

Alpha Channel in Movies

It is often very useful to be able to add areas of transparency to a layer when using Mbox. Transparency can 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.

ProRes 4444 and Hap Alpha Codecs

When creating content, there are quite a few QuickTime codecs that allow an alpha channel (transparency information) to
be embedded in a movie. But for the purposes of Mbox, the only useful codecs are ProRes 4444+, Hap Alpha, and Hap
Q Alpha. Encoding content using one of these three codecs (especially ProRes 4444) can result in movies having a very
high bitrate.
If a movie is created using the ProRes 4444 codec and played on Mbox, the enhanced 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 reasonable bit-rate (< 200mbits/sec), the movie may not play very
smoothly, and playback on other layers of the server may be affected to some extent.
Movies that use the Hap codec are encoded in a special way to enable them to be decompressed by the GPU on the
computer. Because of this they are a special case, they are not handled by the enhanced playback engine or the default
AVFoundation engine. However, this does not mean that they play badly. In fact, movies encoded with the Hap codec
have relatively low bitrates for their quality level. It is possible to get the bitrate of a Hap Q Alpha movie to be too high
though so try to keep their bitrate below 200Mbits/sec.

Still Images

Mbox can play back several different still image file types. JPEG, PNG, TIFF are the three recommended types, and of
those three, PNG is probably the most useful. JPEG has reasonable quality, but does not support an alpha channel.
TIFF can have very high quality (uncompressed quality) and supports an alpha channel, but the file size can be very
large. PNG manages to have good quality and supports an alpha channel, but also keeps the file size very small.
There are a few guidelines for still images:
+ Resolution - use the smallest image possible that provided the desired quality result when scaled correctly for the
show. Using an overly large image and scaling down doesn't provide better results that using a correctly-sized
image. And scaling an image up can reduce quality quite quickly.
+ Quality/Compression Level - use a quality that displays the image accurately, but which keeps the file size
manageable and which allows Mbox to display the image without any latency between selecting the image on the
controller and the image appearing onscreen.
+ Color depth - Mbox can open and display still images using both 8-bit and 16-bit color. However, all files are
rendered onscreen using 8-bit color. Therefore, for normal purposes, there is no advantage to using 16-bit files.
+ Colorspace - the colorspace profile of still images in Mbox is important. Whenever possible, make sure to use
the sRGB profile when saving still images (i.e. assign the sRGB profile to the image and make sure the profile is
embedded in the image when saved). If a different color profile is used, the still images will not have accurate color.

Audio

Audio file creation for Mbox can be one of the more complicated tasks in content creation. Mbox can play audio in two
separate ways: sidecar audio files or embedded audio within the QuickTime movie. (Refer to
99 for more information)
"Audio Output" on page
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