Performance Tips; Movie Compression; Memory Usage - Numark NuVJ Manuel De Référence

PERFORMANCE TIPS

It is very important to note that popular compressions schemes are very inefficient
for VJ'ing. Video files using these compression schemes will behave 'correctly' when
used at nominal speed (100%), but will be very sluggish if you change their playback
speed or scratch them. This remark is valid for mpeg, divx and DV codecs, among
others. If you use these compression formats, you will get poor performance from the
software.
Attaining good performance with video can be difficult because it depends on a lot of different factors.
The most important factors are:
CPU speed
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Disk speed
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RAM access speed
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Video hardware & video bus speed
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Movie compression

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There is no easy way to give a definitive answer in terms of what is best for every computer setting. In
NuVJ, most of the graphic processing is done in the video hardware, so the more powerful it is, the better
performance you are going to get. The CPU is mainly used to decompress movie frames from the disk and
send them to the video card. The faster your drives are, the faster frames will be loaded in the memory and
the faster your CPU is, the faster it will decompress the frames. To achieve a good frame rate with a given
hardware, you can:
Adapt the resolution of the internal computation. See (Preferences/Display)
•
• Use the performance slider to find a balance between quality and performance that is adapted to your
hardware.
Use source material that is adapted to your hardware. If you have a slow disk or older generation of
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hardware, try working with smaller video sources to minimize the impact of loading and
decompressing the movie. Since all calculations are done inside the video hardware, aliasing effects
will be minimized by the automatic filtering applied when the images are scaled to the final resolution.
Movie Compression
Beside movie size, their compression scheme has a huge impact both on the fluidity of the display and their
playability. The more complex the compression scheme, the more work the processor will have to do to
recover specific frames, resulting in sluggish performance. In addition to the compression method itself,
there's the issue of key frames. Most widely spread compression mechanism work using incremental
methods, which means they construct a frame by storing the difference between a frame and the previous
one. In order to keep the process from deriving too much from the original material, they store an original
frame every now and then, and start again coding incremental information from that frame on. These
original frames are called 'key frames'. Using sparse key frames will mean that for NuVJ to access a given
frame, it will have to find the previous key frame and process all the intermediate frame differences until it
reaches the desired one. As you can imagine, this process is rather slow and prevents fast access to frames,
which is very important for backward playback or scratching. That's why compression schemes like mpeg or
DivX are not at all suited for video performances.

Memory usage

Movies are pretty big memory eaters. Depending on their size and length they can use a lot of space very
fast. When a file is imported in NuVJ, it is kept in memory even if it is not assigned to any cell. This is so
that you can use the 'visual' browser to look for files which have already been loaded, without having to
browse and import them again. When the memory of the computer is getting full, its performance can
decrease so it is important to keep an eye on that factor. To release unused movies from the software, you
have to 'purge' them. This can be accomplished in several ways:
1. By manually purging the movies using the menu 'Edit/Purge Visuals'
2. Using the auto-purge feature, which can be set in the Preferences/Advanced dialog. Auto-purge will let
you select a time or memory threshold which, when reached, will automatically purge the unused movies
from your computer's memory. For more information about that feature, please refer to the Preferences
section of this manual.
From our experience, the best compression scheme for video performance
is QuickTime's Photo JPEG with a quality setting of about 80% or more.
This will ensure smooth playback, effective scratching and decent file size.
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