FFMPEG 4.4 如何在 Windows 上将 NV12 格式转换为 YUV420？

Question

我想使用FFmpeg将输入的NV12格式转换为YUV420P。
我尝试使用 sws_scale 转换，但颜色都是绿色。
我已使用 sws 成功将 Y​​UYV422 转换为 420P，但无法将 NV12 转换为 YUV420。
我应该改变什么？

这是我的代码：

QStringList inList = int_put_res.split("x");

m_in_width = inList[0].toInt();

m_in_hieght = inList[1].toInt();

QStringList outList = out_put_res.split("x");

m_out_width = outList[0].toInt();

m_out_hieght = outList[1].toInt();

int VSize = m_in_width * m_in_hieght;

AVPacket *packet;

AVCodecContext *enc_ctx = NULL;

AVFrame *image_inFrame= nullptr;

packet = av_packet_alloc();

int ret = 0;

int base = 0; 

image_inFrame = av_frame_alloc();

open_encoder(m_out_width,m_out_hieght, &enc_ctx);

switch (AVPixelFormat(m_fmt_ctx->streams[m_videoindex]->codecpar->format))
{
case AV_PIX_FMT_YUV420P:
     m_yuv420p_convert_ctx = initSWS(image_inFrame,NULL,m_in_width,m_in_hieght,AV_PIX_FMT_YUV420P,AV_PIX_FMT_YUV420P);
    break;
case AV_PIX_FMT_YUYV422:
      m_yuv420p_convert_ctx = initSWS(image_inFrame,NULL,m_in_width,m_in_hieght,AV_PIX_FMT_YUYV422,AV_PIX_FMT_YUV420P);
    break;
case AV_PIX_FMT_NV12:
      m_yuv420p_convert_ctx = initSWS(image_inFrame,NULL,m_in_width,m_in_hieght,AV_PIX_FMT_NV12,AV_PIX_FMT_YUV420P);
    break;

}


m_frame = create_frame(m_out_width, m_out_hieght);

AVPacket *newpkt = av_packet_alloc();
if (!newpkt)
{
    spdlog::error("failed to alloc avpacket!");
    goto __ERROR;
}
if (!m_fmt_ctx)
{

    goto __ERROR;
}
while (m_isStop != true)
{
    if(av_read_frame(m_fmt_ctx, packet) != 0) {
        goto __ERROR;
    }

    getSWS(m_yuv420p_convert_ctx,packet,image_inFrame,m_frame);
    av_packet_unref(packet);


    m_frame->pts = base++;
    
}

---

SwsContext *FFSDK::initSWS(AVFrame *scrFrame, AVFrame *dstFrame, int 
image_width, int image_height,enum AVPixelFormat scrFmt, enum 
AVPixelFormat dstFmt)

if(scrFrame != NULL){
    av_image_alloc(scrFrame->data, scrFrame->linesize,image_width, image_height, scrFmt, 1);
}

if(dstFrame != NULL){
    av_image_alloc(dstFrame->data, dstFrame->linesize, m_out_width, m_out_hieght, dstFmt, 1);
}

return  sws_getContext(image_width,image_height,
                       scrFmt,
                       m_out_width, m_out_hieght, dstFmt,
                       SWS_BICUBIC,
                       nullptr,
                       nullptr,
                       nullptr);

}

void FFSDK::getSWS(SwsContext *context,AVPacket *packet,AVFrame *scrFrame, AVFrame *dstFrame)
{

    scrFrame->data[0] = packet->data;
    sws_scale(context,
              scrFrame->data,
              scrFrame->linesize, 0, m_in_hieght, dstFrame->data,
              dstFrame->linesize);
}

Answer 1

从您发布的代码片段中我看不出问题。

绿色通常是零数据的结果（Y、U 和 V 的所有元素都是零）。
零内容的原因可能是没有任何内容写入视频帧的目标（或源）缓冲区。

---

我创建了一个“自包含”代码示例，演示了使用 sws_scale 从 NV12 到 YUV420 的转换。

• 首先使用 FFmpeg（命令行工具）构建合成输入帧。
  该命令以原始 NV12 格式创建 320x240 视频帧：

    ffmpeg -y -f lavfi -i testsrc=size=320x240:rate=1 -vcodec rawvideo -pix_fmt nv12 -frames 1 -f rawvideo nv12_image.bin
  

---

下一个代码示例应用以下阶段：

• 为源帧分配内存（NV12 格式）。
• 从二进制文件中读取 NV12 数据（用于测试）。
• 为目标帧分配内存（YUV420 格式）。
• 应用色彩空间转换（使用sws_scale）。
• 将转换后的 YUV420 数据写入二进制文件（用于测试）。

完整代码如下：

//Use extern "C", because the code is built as C++ (cpp file) and not C.
extern "C"
{
    #include <libswscale/swscale.h>
    #include <libavformat/avformat.h>
    #include <libswresample/swresample.h>
    #include <libavutil/pixdesc.h>
    #include <libavutil/imgutils.h>
}


int main()
{
    int width = 320;
    int height = 240;   //The code sample assumes height is even.
    int align = 0;
    AVPixelFormat srcPxlFormat = AV_PIX_FMT_NV12;
    AVPixelFormat dstPxlFormat = AV_PIX_FMT_YUV420P;
    int sts;

    //Source frame allocation
    ////////////////////////////////////////////////////////////////////////////
    AVFrame* pNV12Frame = av_frame_alloc();   

    pNV12Frame->format = srcPxlFormat;
    pNV12Frame->width = width;
    pNV12Frame->height = height;

    sts = av_frame_get_buffer(pNV12Frame, align);

    if (sts < 0)
    {
        return -1;  //Error!
    }
    ////////////////////////////////////////////////////////////////////////////


    //Read NV12 data from binary file (for testing)
    ////////////////////////////////////////////////////////////////////////////
    //Use FFmpeg for building raw NV12 image (used as input).
    //ffmpeg -y -f lavfi -i testsrc=size=320x240:rate=1 -vcodec rawvideo -pix_fmt nv12 -frames 1 -f rawvideo nv12_image.bin

    FILE *f = fopen("nv12_image.bin", "rb");

    if (f == NULL)
    {
        return -1;  //Error!
    }

    //Read Y channel from nv12_image.bin (Y channel size is width x height).
    //Reading row by row is required in rare cases when pNV12Frame->linesize[0] != width
    uint8_t *Y = pNV12Frame->data[0];   //Pointer to Y color channel of the NV12 frame.
    for (int row = 0; row < height; row++)
    {
        fread(Y + (uintptr_t)row * pNV12Frame->linesize[0], 1, width, f); //Read row (width pixels) to Y0.
    }

    //Read UV channel from nv12_image.bin (UV channel size is width x height/2).
    uint8_t* UV = pNV12Frame->data[1];   //Pointer to UV color channels of the NV12 frame (ordered as UVUVUVUV...).
    for (int row = 0; row < height/2; row++)
    {
        fread(UV + (uintptr_t)row * pNV12Frame->linesize[1], 1, width, f); //Read row (width pixels) to UV0.
    }

    fclose(f);
    ////////////////////////////////////////////////////////////////////////////



    //Destination frame allocation
    ////////////////////////////////////////////////////////////////////////////
    AVFrame *pYUV420Frame = av_frame_alloc();

    pYUV420Frame->format = dstPxlFormat;
    pYUV420Frame->width = width;
    pYUV420Frame->height = height;

    sts = av_frame_get_buffer(pYUV420Frame, align);

    if (sts < 0)
    {
        return -1;  //Error!
    }
    ////////////////////////////////////////////////////////////////////////////


    //Color space conversion
    ////////////////////////////////////////////////////////////////////////////
    SwsContext *sws_context = sws_getContext(width,
                                             height,
                                             srcPxlFormat,
                                             width,
                                             height,
                                             dstPxlFormat,
                                             SWS_FAST_BILINEAR,
                                             NULL,
                                             NULL,
                                             NULL);

    if (sws_context == NULL)
    {
        return -1;  //Error!
    }

    sts = sws_scale(sws_context,             //struct SwsContext* c,
                    pNV12Frame->data,        //const uint8_t* const srcSlice[],
                    pNV12Frame->linesize,    //const int srcStride[],
                    0,                       //int srcSliceY, 
                    pNV12Frame->height,      //int srcSliceH,
                    pYUV420Frame->data,      //uint8_t* const dst[], 
                    pYUV420Frame->linesize); //const int dstStride[]);    

    if (sts != pYUV420Frame->height)
    {
        return -1;  //Error!
    }
    ////////////////////////////////////////////////////////////////////////////


    //Write YUV420 data to binary file (for testing)
    ////////////////////////////////////////////////////////////////////////////
    //Use FFmpeg for converting the binary image to PNG after saving the data.
    //ffmpeg -y -f rawvideo -video_size 320x240 -pixel_format yuv420p -i yuv420_image.bin -pix_fmt rgb24 rgb_image.png

    f = fopen("yuv420_image.bin", "wb");

    if (f == NULL)
    {
        return -1;  //Error!
    }

    //Write Y channel to yuv420_image.bin (Y channel size is width x height).
    //Writing row by row is required in rare cases when pYUV420Frame->linesize[0] != width
    Y = pYUV420Frame->data[0];   //Pointer to Y color channel of the YUV420 frame.
    for (int row = 0; row < height; row++)
    {
        fwrite(Y + (uintptr_t)row * pYUV420Frame->linesize[0], 1, width, f); //Write row (width pixels) to file.
    }

    //Write U channel to yuv420_image.bin (U channel size is width/2 x height/2).
    uint8_t* U = pYUV420Frame->data[1];   //Pointer to U color channels of the YUV420 frame.
    for (int row = 0; row < height/2; row++)
    {
        fwrite(U + (uintptr_t)row * pYUV420Frame->linesize[1], 1, width/2, f); //Write row (width/2 pixels) to file.
    }

    //Write V channel to yuv420_image.bin (V channel size is width/2 x height/2).
    uint8_t* V = pYUV420Frame->data[2];   //Pointer to V color channels of the YUV420 frame.
    for (int row = 0; row < height/2; row++)
    {
        fwrite(V + (uintptr_t)row * pYUV420Frame->linesize[2], 1, width/2, f); //Write row (width/2 pixels) to file.
    }

    fclose(f);
    ////////////////////////////////////////////////////////////////////////////


    //Cleanup
    ////////////////////////////////////////////////////////////////////////////
    sws_freeContext(sws_context);
    av_frame_free(&pYUV420Frame);
    av_frame_free(&pNV12Frame);
    ////////////////////////////////////////////////////////////////////////////

    return 0;
}

---

用于验证输出：

• 执行完代码后，执行FFmpeg（命令行工具）。
  以下命令将原始二进制帧（YUV420 格式）转换为 PNG（RGB 格式）。

    ffmpeg -y -f rawvideo -video_size 320x240 -pixel_format yuv420p -i yuv420_image.bin -pix_fmt rgb24 rgb_image.png
  

---

输出样例（YUV420转PNG图片文件格式后）：

---

希望能帮助你找到问题...