PRG Mbox Designer Manual 3.9 - Manual (Page 167)

MBOX ® MEDIA SERVER USER MANUAL 159
+ Other codecs, when treated as non-preferred, are played in a QuickTime "wrapper" rather than natively in Mbox.
Because of this, playback may be poor, playmodes other than FWD Loop and FWD Once may not work, movies
may not loop unless the in/out points are rolled inwards slightly, frame blending will not work, and some
transitions and effects may not work properly. On the plus side, embedded audio tracks in movies with non-
preferred codecs may play when the movie is played. To force Mbox to attempt to play non-preferred codecs
natively, however, this is not recommended. Please contact your PRG representative if you would like further
information about this feature.
Compression (Bit Rate)
Movie compression can have a large impact on playback performance. There is a balance between quality and
performance that can be tipped in either direction by adjusting the amount of compression when a movie is rendered.
Typically, compression is labeled as "Compressor Quality" or something similar and the scale goes from "least" to
"best" or 0% to 100% - more compression to less compression. The more compression used, the smaller the movie
file will be and the bit rate (or data rate) of the movie will be lower. Lower bit rates theoretically lead to better playback
performance, but below a certain point the quality may be unacceptable. Alternately, lowering compression will
provide a higher quality movie, but due to a higher bit rate, playback performance may suffer. At a certain limit in
either direction there will be a point of diminishing returns where either quality or playback is unacceptable. Typically,
Mbox will provide the best performance to quality ratio at Medium or 50%-60%. Higher quality settings may not look
noticeably better for the trade-off in performance. As a rule of thumb, movie bit rates should be kept below 65Mbits/
sec in order to play content on multiple layers at the same time. In special circumstances, Mbox can handle bit rates
up to approximately 200Mbits/sec.
Frame Rate
Movie frame rate may also need to be considered when creating content for Mbox. For optimal results, content
should be rendered at a frame rate that is a divisor of the current Fullscreen mode output frequency. Therefore, if the
Fullscreen mode has a 60Hz refresh, movies that play at 30fps will synchronize nicely with the output of the Mac
Graphics card (each frame of the movie will be repeated twice to equal two fields of the output). While content with
lesser frame rates will work, there may be some noticeable effects. In the above example, if the movie has fewer than
30fps, then the Graphics card will need to repeat some frames more than twice and the movie may appear to play
less smoothly. Depending on the frame rate of the movie, this effect may be more or less noticeable. If the movie’s
frame rate divides evenly into 60 then the movie will play more smoothly; so 20fps content will look better than 24fps
content. So if the Mbox output frequency is 50Hz, then it would be best to create content that is rendered at 25fps. If
output frequency is 59.94Hz, then content should be rendered at 29.97fps, and so on. (Refer to
"Setup: Fullscreen
Mode" on page 58 for more information about setting the output frequency.)
Resolution
As noted above, movie resolution has an impact on the performance of the Mbox server. To put it simply, the larger
the movie’s pixel dimensions, the harder it is to play. For best results, always try to play the smallest movie possible.
Furthermore, always make sure that the Mbox texture size setting is no larger than the largest piece of content that
you intend to play. Setting the texture size larger than necessary will affect movie playback. Of course there are
factors outside of Mbox that need to be taken into consideration when choosing a content resolution - type of output
signal, display device native resolution, size of projection surface- but for the most part, there is not much point in
playing content that has a higher resolution than the selected Fullscreen output size. But admittedly, sometimes the
smallest possible movie is not the one that looks the best with your particular setup, so make sure to test in advance
if possible.
Audio
Audio file manipulation for Mbox is one of the more complicated tasks in content creation. Particularly, AIFF audio
files that are associated with movie files rather than audio that is embedded in movies that use non-preferred codecs.
Remember that audio playback cannot be sped up or slowed down when using associated AIFF files, and that audio
files will loop when the movie hits its out-point. So it is imperative to make sure that an audio file’s playback rate
matches the movie’s default playback rate, and that the audio file is exactly the same length as the movie. The best
way to do this is to keep the audio and video components of movies together until the very last minute (all throughout
the editing process). Once the editing process is complete, then separate the two files. Try to avoid any manipulations