树莓派4基于FFmpeg libavcodec实现毫秒级RGBA图像压缩优化求助

我们需要在树莓派4上通过C/C++程序，将生成的1024×2048的32位RGBA原始图像（大小8MB）压缩至JPEG级别（200-500KB），且压缩耗时需控制在数毫秒内，否则对我们毫无意义。

我们尝试使用FFmpeg开发库及C/C++代码进行编码，但修改官方编码示例后，得到的耗时结果无法接受。

修改后的帧创建代码 #

for (i = 0; i < 25; i++)
{
#ifdef MEASURE_TIME
        auto start_time = std::chrono::high_resolution_clock::now();
        std::cout << "START Encoding frame...\n";
#endif
    fflush(stdout);

    ret = av_frame_make_writable(frame);
    if (ret < 0)
        exit(1);

    // 将32位RGBA图像转换为YUV像素格式
    for (y = 0; y < c->height; y++)
    {
        for (x = 0; x < c->width; x++)
        {
            int imageIndexY = y * frame->linesize[0] + x;

            uint32_t rgbPixel = ((uint32_t*)OutputDataImage)[imageIndexY];

            double Y, U, V;
            uint8_t R = rgbPixel << 24;
            uint8_t G = rgbPixel << 16;
            uint8_t B = rgbPixel << 8;

            YUVfromRGB(Y, U, V, (double)R, (double)G, (double)B);
            frame->data[0][imageIndexY] = (uint8_t)Y;

            if (y % 2 == 0 && x % 2 == 0)
            {
                int imageIndexU = (y / 2) * frame->linesize[1] + (x / 2);
                int imageIndexV = (y / 2) * frame->linesize[2] + (x / 2);

                frame->data[1][imageIndexU] = (uint8_t)U;
                frame->data[2][imageIndexV] = (uint8_t)Y;
            }
        }
    }

    frame->pts = i;

    /* 编码图像 */
    encode(c, frame, pkt, f);

#ifdef MEASURE_TIME
        auto end_time = std::chrono::high_resolution_clock::now();
        auto time = end_time - start_time;
        std::cout << "FINISHED Encoding frame in: " << time / std::chrono::milliseconds(1) << "ms.\n";

#endif
    }

函数前序关键代码 #

codec_name = "mpeg4";

codec = avcodec_find_encoder_by_name(codec_name);

c = avcodec_alloc_context3(codec);
    
c->bit_rate = 1000000;  
c->width = IMAGE_WIDTH;
c->height = IMAGE_HEIGHT;
c->gop_size = 1;
c->max_b_frames = 1;
c->pix_fmt = AV_PIX_FMT_YUV420P;   

其中IMAGE_WIDTH和IMAGE_HEIGHT分别为1024和2048。

树莓派4上的运行结果 #

START Encoding frame...
Send frame   0
FINISHED Encoding frame in: 40ms.
START Encoding frame...
Send frame   1
Write packet   0 (size=11329)
FINISHED Encoding frame in: 60ms.
START Encoding frame...
Send frame   2
Write packet   1 (size=11329)
FINISHED Encoding frame in: 58ms.

其余相关代码 #

void RGBfromYUV(double& R, double& G, double& B, double Y, double U, double V)
{
    Y -= 16;
    U -= 128;
    V -= 128;
    R = 1.164 * Y + 1.596 * V;
    G = 1.164 * Y - 0.392 * U - 0.813 * V;
    B = 1.164 * Y + 2.017 * U;
}

求助需求 #

我在编码及Codec使用方面完全是新手，现寻求最优实现方案，希望将压缩耗时降至数毫秒，同时不确定当前选择的Codec或像素格式是否合适，盼得到专业指导。

内容的提问来源于stack exchange，提问作者Jerry Switalski