swsscale

Swsscale, commonly referred to as libswscale, is a software library in the FFmpeg project that performs image scaling and pixel format conversion for video frames. It provides a set of utilities to resize images and convert between various color spaces and pixel formats, independently of the surrounding decoding or encoding pipeline.

The library supports a broad range of resizing algorithms, from nearest neighbor to high-quality filters such as bilinear, bicubic, Lanczos, and spline-based options. It handles color space conversion and pixel format conversion between popular formats such as YUV and RGB, including different chroma subsampling schemes like 4:2:0 and 4:4:4. libswscale is designed to be portable and optimized to use platform-specific SIMD instructions where available (for example, MMX, SSE, or NEON).

Usage is through a SwsContext, created with sws_getContext, configured with input and output formats, sizes, and optionally flags that select the scaling filter. The primary API call is sws_scale, which processes image planes from input to output buffers described by data pointers and linesizes. After processing, resources are released with sws_freeContext. The API supports multi-threaded operation and can be integrated into decoders, encoders, or custom processing pipelines.

Libswscale is a core component in FFmpeg’s workflow, enabling efficient conversion and scaling when bridging different formats between decoders, encoders, and display devices. It is widely used by FFmpeg command-line tools and by other multimedia software that relies on FFmpeg libraries, and is part of FFmpeg’s open-source licensing ecosystem.