libswscale

libswscale is the software scaling library in FFmpeg responsible for image resizing and pixel format conversion of video frames. It provides high-level functionality to resize frames and convert between common pixel formats (for example YUV, RGB, and grayscale), enabling pipelines where input data and output encoders use different formats. libswscale is designed to work alongside other FFmpeg components such as libavcodec and libavutil and is typically used in transcoding and video processing workflows.

At the core is the SwsContext, created with sws_getContext, which encodes the source and destination dimensions and pixel formats, along with optional filtering and quality flags. Once a context is created, sws_scale performs the actual conversion on image planes, taking pointers to source and destination data and their strides. The context is deallocated with sws_freeContext when no longer needed.

libswscale supports a wide range of pixel formats and offers several scaling filters, including bilinear, bicubic, lanczos, gaussian, and sinc-based options. It can perform color space conversion as part of format conversion, which is essential when the input is in a different color space than the encoder expects.

In practical use, libswscale is frequently invoked during video transcoding or format-conversion pipelines to adapt frame size or pixel representation to target devices or codecs. It is one component of FFmpeg's libswscale library and is accessible from various FFmpeg front-ends and APIs.