How to resize a picture using ffmpeg's sws_scale()?

ffmpeg is a powerful multimedia framework used for processing video and audio files. sws_scale is a feature within ffmpeg for resizing images and converting pixel formats.

Using ffmpeg's sws_scale functionality to adjust image size typically involves the following steps:

1. Initialize SWS context (software scaling and conversion context): You must create a SwsContext structure, which contains all necessary information for the conversion. Initialize this context by calling the sws_getContext function and passing the width, height, and pixel format of both the source and destination images.

2. Perform scaling operation: Execute the actual scaling using the sws_scale function. Pass the previously initialized SwsContext, the source image data and line stride, and the destination image data and line stride.

3. Release SWS context: After processing, release the context using sws_freeContext to free the allocated resources.

Below is a simplified code example using ffmpeg's libswscale library to adjust image size:

c
#include <libavutil/imgutils.h>
#include <libswscale/swscale.h>

void resize_image(uint8_t **src_data, int src_width, int src_height, enum AVPixelFormat src_pix_fmt,
                  uint8_t **dst_data, int dst_width, int dst_height, enum AVPixelFormat dst_pix_fmt) {
    // Initialize SWS context
    struct SwsContext *sws_ctx = sws_getContext(
        src_width, src_height, src_pix_fmt,
        dst_width, dst_height, dst_pix_fmt,
        SWS_BILINEAR, NULL, NULL, NULL);

    if (!sws_ctx) {
        fprintf(stderr, "Could not initialize the SWS context\n");
        return;
    }

    // Perform scaling operation
    sws_scale(sws_ctx,
              (const uint8_t * const *)src_data, src_linesize,
              0, src_height,
              dst_data, dst_linesize);

    // Release SWS context
    sws_freeContext(sws_ctx);
}

int main() {
    // Assuming src_data, dst_data, src_linesize, and dst_linesize have been properly initialized
    // Allocate memory and set the format and size of the source and destination images according to your requirements

    // Call the resize_image function
    resize_image(src_data, src_width, src_height, AV_PIX_FMT_YUV420P,
                 dst_data, dst_width, dst_height, AV_PIX_FMT_RGB24);

    // Additional processing...

    return 0;
}

In the above example, it is assumed that the source and destination image data (src_data and dst_data) have been properly initialized based on their formats and sizes. src_linesize and dst_linesize represent the line strides for the source and destination images, respectively, which can typically be obtained by calling the av_image_alloc function.

This is a simplified example and may not fully align with specific application scenarios or requirements. You may need to implement error handling, memory management, and other pixel processing operations to meet your particular needs.