Rendering animation can take a lot of time. Unfortunately Blender (at least up to version2.79b (Mar 2018)) does not offer a pause/resume function while rendering, but this post will introduce settings and a workaround to this potential problem.
The ultimate goal is to be able to secure animation renders to reduce the incidences of having to re-render entire scenes. Two of the biggest problems I encounter while rendering animation are that I use my PC for other tasks too and that we have an irregular electricity supply. Having an interruption traditionally means that the entire scene has to be re-rendered. By using the setup below the animation render can be ‘paused’ or stopped at any time, and ‘resuming’ can take place irrespective the reason the render has been stopped.
This method will work with any renderer (Blender Render and Cycles Render) and can be used in combination with planning frames and sharing resources.
The Blender rendering process
To render an image or scene in Blender the Render tab is used. For the purpose of this post, the important settings in the Render tab include the frame or frames that need to be rendered, the output directory, the render dimentions and the file format. By default, Blender will render PNG files and save then in the /tmp/ directory on the root directory of your PC.
‘Pausing’ and ‘resuming’ animation rendering in Blender
In principle, the idea is to render animation as individual images and, then afterwards, adding them together to create a movie file. By rendering as images instead of one movie file, the last frame (where the render was ‘paused’ or inturrupted) can be inspected and can be used to set the first frame to start off with.
Render individual files
Animation in Blender can be rendered as individual image files or as movie files. The first thing one tend to do when rendering animation in Blender is to set the output to a movie file. This will mean that if the render was interrupted (for whatever reason), the file will break – and all the selected frames will have to be re-rendered.
Instead of choosing a movie file format, rather set this to an image file format. The default is PNG, which will be perfect in most cases. After the file format has been chosen, one might also want to choose a more appropriate directory where the files will be saved. Overwrite is selected by default, which is also what you might want in this case.
The rendering process can now continue as usual, but after each frame has been completed, it will be saved as a single file in the chosen directory. Each file will be saved with the frame number as name. By selecting Overwrite, sections of the scene can be set to be re-rendered if needed without adding additional files to the rendering directory.
Evaluating the rendered files and their file names
No matter the reason, whether the rendering process was stopped or interrupted by any other means, the chosen directory will contain all the files that has been successfully rendered. By looking at the last rendered file and its file name, the first frame can be established to continue an interrupted render process. In other words, if a scene has 100 frames and the last frame after the interruption is frame 29, then Blender can be set to start rendering from frame 30 again. If the animation render process has been completed, the last frame can be noted down for rendering the frame files into a movie file.
Rendering the frame files into a movie file
After all the required frames have been rendered, each into their own file, the files can be combined to create a movie file. To do this, open a new instance fo Blender and open the Video Editing layout from the screen layout section. Click on Add -> Images and select all the rendered frames/files in the above chosen directory (press A) and press the Add Image Strip button.
The frames will now appear on the Video Sequence Editor’s timeline control similar to the Timeline and Playback controls in the Default layout. By going back to the Default layout in the screen layout section, the frames can be combined into a different file format, i.e. a movie file format, by using the Render tab and Animation button again. Remember to set the output directory, match the End: frames and to set the Resolution matches the resolution the frame files was rendered at.