Adding External Libraries in Blender

Intro

In my proposal, I mentioned that the Rubber Band Library, a 3rd-party library compatible with Blender’s open source license, could be used to implement pitch correction into Blender’s video sequence editor (VSE). This would mean that we wouldn’t have to implement the algorithm manually! However, before proceeding with this approach, there several things that had to be considered:

• Build Complexity - Evaluating how difficult/complex the build process is
• Build Size - Is it binary size small enough to be integrated into Blender?

As a preliminary task, I wanted to attempt to build the Rubber Band Library and looked at extern/audaspace to better understand Blender’s build process. Surprisingly enough, I’ve never used CMAKE (though I have used makefile before) nor never downloaded a library for any of my C++ programs during university. So, I thought it would be a good to try to utilize the Rubber Band Library on a bare bones command-line program, where you can specify the input audio file and then the output audio file at 2x speed which will be pitch-corrected by the library.

Compiling the Rubber Band Library (TODO)

After downloading the source code, I looked at COMPILING.md which had some references to Meson but more importantly… something about RubberBandSingle.cpp and adding it as a static library, which is the approach I went with…

File Structure:

RubberBandTest
├─ CMakeLists.txt
├─ beatles.wav
├─ main.cpp
└─ rubberband

Library Usage (TODO)

Notes to add and explain…

• Initialize the RubberBandStretcher class with options
• Mention the setTimeRatio() method, where setTimeRatio(0.5) makes the audio 2x quicker and setTimeRatio(2.0) makes the audio 0.5x quicker. Both preserve pitch.
• Mention the study and process method. The process method does the actual transformation on the float vector audio data.
• Get the processed audio with the retrieve method…
• Mention option to shift pitch too though setPitchScale method.

Some Results

Original Audio:

from IPython.display import Audio
Audio("beatles_orig.wav", rate=48000)

2x Speed:

0.5x Speed:

The code for this example can be found here… [TODO]

Checking the static library librubberband_static.a, the library size is 2.6 MB.

Here’s RubberBandSingle.cpp