Background Rendering
Background rendering causes temporary output to be rendered
constantly while the timeline is being modified. The temporary
output is displayed during playback whenever possible. This is
useful for transitions and previewing effects that are too slow to
display in real time. If a Render Farm is enabled, the render farm
is used for background rendering. This gives you the potential for
real-time effects if enough network bandwidth and CPU nodes exist.
Background rendering is enabled in the Performance tab of
the Preferences window. It has one interactive function
Settings
→ Toggle background rendering . This
sets the point where background rendering starts up to the position
of the insertion point. If any video exists, a red bar appears in
the time ruler showing what has been background rendered
(figure 7.9). Because this creates a very large number
of files, a Shell Command script is available to delete them if in the
default location.
Figure 7.9:
Settings Background Rendering
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It is often useful to insert an effect or a transition and then
select Settings
→ Toggle background rendering
right before the effect to preview it in real time and full frame
rates (figure 7.10).
Figure 7.10:
Timeline with the top red bar
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- Frames per background rendering job
- This only works if a
Render Farm is being used; otherwise, background rendering creates a
single job for the entire timeline. The number of frames specified
here is scaled to the relative CPU speed of rendering nodes and used
in a single render farm job. The optimum number is 10 - 30 since
network bandwidth is used to initialize each job.
- Frames to preroll background
- This is the number of frames to
render ahead of each background rendering job. Background rendering
is degraded when preroll is used since the jobs are small. When
using background rendering, this number is ideally 0. Some effects
may require 3 frames of preroll.
- Output for background rendering
- Background rendering
generates a sequence of image files in a certain directory. This
parameter determines the filename prefix of the image files. It
should be accessible to every node in the render farm by the same
path. Since hundreds of thousands of image files are usually
created, ls commands will not work in the background rendering
directory. The browse button for this option normally will not work
either, but the configuration button for this option works. The
default value will be /tmp/brender . Because using background
rendering creates a voluminous number of brender numbered files,
a Shell Command script is available to delete them if they are
in the default /tmp/brender format.
- File format
- The file format for background rendering has to
be a sequence of images. The format of the image sequences
determines the quality and speed of playback. JPEG generally works
well and is the default.
Tip: If you have rendered your whole project with File format
set to JPEG and there are no missing numbers in the sequence, you can
create a video from that sequence outside of CINELERRA-GG.
For example, if using the default output so that your files are named
/tmp/brender000000, /tmp/brender000001, ... in a window, you would type:
ffmpeg -f image2 -i /tmp/brender0%5d -c:v copy brender.mov
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which would create the video file brender.mov - be sure to delete
existing brender files before creating a new sequence to ensure there
are no missing numerical values in the sequence.
The CINELERRA-GG Community, 2021
https://www.cinelerra-gg.org
