AVFrame 拷贝到CVPixelBufferRef 的过程

//Not used on OSX - frame is never copied.
static int copy_avframe_to_pixel_buffer(AVCodecContext   *avctx,
                                        const AVFrame    *frame,
                                        CVPixelBufferRef cv_img,
                                        const size_t     *plane_strides,
                                        const size_t     *plane_rows)
{
    int i, j;
    size_t plane_count;
    int status;
    int rows;
    int src_stride;
    int dst_stride;
    uint8_t *src_addr;
    uint8_t *dst_addr;
    size_t copy_bytes;

    status = CVPixelBufferLockBaseAddress(cv_img, 0);
    if (status) {
        av_log(
            avctx,
            AV_LOG_ERROR,
            "Error: Could not lock base address of CVPixelBuffer: %d.\n",
            status
        );
    }

    if (CVPixelBufferIsPlanar(cv_img)) {
        plane_count = CVPixelBufferGetPlaneCount(cv_img);
        for (i = 0; frame->data[i]; i++) {
            if (i == plane_count) {
                CVPixelBufferUnlockBaseAddress(cv_img, 0);
                av_log(avctx,
                    AV_LOG_ERROR,
                    "Error: different number of planes in AVFrame and CVPixelBuffer.\n"
                );

                return AVERROR_EXTERNAL;
            }

            dst_addr = (uint8_t*)CVPixelBufferGetBaseAddressOfPlane(cv_img, i);
            src_addr = (uint8_t*)frame->data[i];
            dst_stride = CVPixelBufferGetBytesPerRowOfPlane(cv_img, i);
            src_stride = plane_strides[i];
            rows = plane_rows[i];

            if (dst_stride == src_stride) {
                memcpy(dst_addr, src_addr, src_stride * rows);
            } else {
                copy_bytes = dst_stride < src_stride ? dst_stride : src_stride;

                for (j = 0; j < rows; j++) {
                    memcpy(dst_addr + j * dst_stride, src_addr + j * src_stride, copy_bytes);
                }
            }
        }
    } else {
        if (frame->data[1]) {
            CVPixelBufferUnlockBaseAddress(cv_img, 0);
            av_log(avctx,
                AV_LOG_ERROR,
                "Error: different number of planes in AVFrame and non-planar CVPixelBuffer.\n"
            );

            return AVERROR_EXTERNAL;
        }

        dst_addr = (uint8_t*)CVPixelBufferGetBaseAddress(cv_img);
        src_addr = (uint8_t*)frame->data[0];
        dst_stride = CVPixelBufferGetBytesPerRow(cv_img);
        src_stride = plane_strides[0];
        rows = plane_rows[0];

        if (dst_stride == src_stride) {
            memcpy(dst_addr, src_addr, src_stride * rows);
        } else {
            copy_bytes = dst_stride < src_stride ? dst_stride : src_stride;

            for (j = 0; j < rows; j++) {
                memcpy(dst_addr + j * dst_stride, src_addr + j * src_stride, copy_bytes);
            }
        }
    }

    status = CVPixelBufferUnlockBaseAddress(cv_img, 0);
    if (status) {
        av_log(avctx, AV_LOG_ERROR, "Error: Could not unlock CVPixelBuffer base address: %d.\n", status);
        return AVERROR_EXTERNAL;
    }

    return 0;
}