FFmpeg：视频帧格式转化（sws_scale）（参考scaling_video.c）

如果不是特别熟悉C/C++，又要使用FFmpeg.API处理一些简单的音视频业务，那么可以使用org.bytedeco:ffmpeg-platform，下面记录一下使用ffmpeg-platform视频帧格式转化的方法。

1. 代码实现

视频帧转化在处理视频转码时比较常见，比如要将RGB24转成YUV420P，下面一个将YUV420P的视频帧转成RGB24的例子：

public class ScalingVideo {

    public static void scaling_video(String output, int width, int height) throws IOException {
        SwsContext sws_ctx = null;
        PointerPointer<BytePointer> src_data = new PointerPointer<>(4);
        PointerPointer<BytePointer> dst_data = new PointerPointer<>(4);
        IntPointer src_linesize = new IntPointer(4);
        IntPointer dst_linesize = new IntPointer(4);
        try (OutputStream os = new FileOutputStream(output)) {
            int src_w = 352, src_h = 288;
            int src_pix_fmt = AV_PIX_FMT_YUV420P, dst_pix_fmt = AV_PIX_FMT_RGB24;

            sws_ctx = sws_getContext(src_w, src_h, src_pix_fmt, width, height, dst_pix_fmt, SWS_BICUBIC, null, null,
                    (DoublePointer) null);
            if (Objects.isNull(sws_ctx)) {
                throw new IOException("sws_getContext error");
            }

            // allocate source and destination image buffers
            int ret = av_image_alloc(src_data, src_linesize, src_w, src_h, src_pix_fmt, 16);
            if (ret < 0) {
                throw new IOException(ret + ":av_image_alloc error");
            }

            // buffer is going to be written to rawvideo file, no alignment
            ret = av_image_alloc(dst_data, dst_linesize, width, height, dst_pix_fmt, 1);
            if (ret < 0) {
                throw new IOException(ret + ":av_image_alloc error");
            }

            byte[] buffer = new byte[ret];

            for (int i = 0; i < 100; i++) {
                fill_yuv_image(src_data, src_linesize, src_w, src_h, i);

                sws_scale(sws_ctx, src_data, src_linesize, 0, src_h, dst_data, dst_linesize);

                dst_data.get(BytePointer.class, 0).get(buffer);
                os.write(buffer);
            }

            System.out.printf(
                    "Scaling succeeded. Play the output file with the command:\n"
                            + "ffplay -f rawvideo -pix_fmt %s -video_size %dx%d %s\n",
                    av_get_pix_fmt_name(dst_pix_fmt).getString(), width, height, output);
        } finally {
            if (Objects.nonNull(sws_ctx)) {
                sws_freeContext(sws_ctx);
            }
            src_data.close();
            src_linesize.close();
            dst_data.close();
            dst_linesize.close();
        }
    }
}

2. 结果展示

转化的RGB24视频数据，有使用ffplay播放，效果如下：

播放命令：

ffplay -f rawvideo -pix_fmt rgb24 -video_size 352x288 t.rgb24