In this brief tutorial, we’ll see how to initiate renderings from the command line and, more importantly, how to queue multiple renderings from different files in succession.
Video Transcript
Hello everyone! In this brief tutorial, we’ll see how to initiate renderings from the command line and, more importantly, how to queue multiple renderings from different files in succession.
These operations are very useful because if you have multiple renderings from different files to perform in sequence, you can schedule their execution in a single batch file. This way, you won’t need to manually check when one rendering is finished to start the next one. You can simply run the batch file and go grab a coffee or even go to sleep, depending on the number of renderings you need to complete.
This tutorial was recorded using Blender version 4.2, but the single line of code that allows you to start renderings from the command line has maintained the same structure across several versions of the software and will likely remain consistent in future versions as well.
If you have a blend file with an active virtual camera, you can render the scene directly from the command line without launching a Blender session with the interface, using the following line of code:
blender.exe -b scenepath.blend -o outputpath -s startframe -e endframe -a
The rendering will be executed with the resolution, output file format, compression, and all other settings exactly as specified in the blend file. Of course, some parameters will need to be replaced!
Specifically, you will need to replace Scene Path with the full path of the blend file to be rendered, including the final blend extension.
Similarly, you will need to replace Output Path with the full path where the rendered files should be saved, optionally specifying a prefix for the files. In this case, you do not need to specify the file extension for the output files.
For Start Frame and End Frame, you must specify the first and last frames to be rendered in the sequence.
The -a option at the end instructs Blender to use the settings present in the file being rendered.
On screen, I am showing an example of an animation rendering initiated from the command line.
Now, let’s move on to the second topic of this tutorial: how to queue multiple renderings in succession using a batch file.
In a previously published tutorial on this channel, I showed another batch command-line application that allowed for exporting models from blend files located in a folder into FBX format, while also specifying the Copy Attributes and Embedded options for PBR Material Textures. If you’re interested in this or other Blender tutorials, leave a Like or a comment on the video and, most importantly, subscribe to the channel so you won’t miss the next ones!
To render multiple Blender files in succession, simply create a text file and add the commands for rendering the blend files, one command per line.
This text file can be created using applications like Notepad or other text editors, but it’s essential to give it the correct extension. On Windows, as in this example, the extension should be bat, short for batch. On Linux or Mac, the files will be shell scripts, typically with the extension sh.
On screen, I’m showing how multiple blend files are rendered in succession, each with its own settings, starting from a single click on the batch file.
More generally, to explore the arguments available for launching Blender from the command line, type blender -h or blender --h and press Enter.
Before wrapping up the tutorial, let’s look at how to run multiple batch files in succession from a single batch file!
I often do this when creating my assets and need to produce renderings for each asset from scene, wireframe, and turntable files. For each asset, I create a batch file that manages the individual renderings of that project. When working on multiple assets, I end up with multiple folders, each containing its own batch file.
In these cases, I focus on creating the assets while I’m at my computer, and then I launch all their batch files in sequence when I’m not at my computer, such as overnight or during the weekends. It’s an excellent way to optimize workflow.
Here too, you’ll need to create a batch file from a new text file. However, unlike running individual renderings by calling Blender within the batch file, here you’ll need to use a specific command called Call.
This command is essential for running multiple batch files in sequence, because without it, the script execution would stop immediately after completing the first batch file listed in the script.
In summary, if you want to execute multiple renderings from a single batch file, there’s no issue. But if you want to run multiple batch files from another batch file, you must use the Call command.
I can’t say this with absolute certainty since I don’t use those environments, but I believe that in shell scripts for Linux and Mac OS, no special commands are required to run multiple external shell scripts in sequence.
For the sake of completeness, I’ll add that by replacing the Call command with the Start command in the batch file on Windows, you can run processes in parallel instead of sequentially. However, in the specific case of renderings, I do not recommend this option.
Well, that’s all for this brief tutorial! I hope you found it helpful! See you soon!