小贝子编程

ffmpeg Bmp to yuv : Crash at sws_scale



上下文：我有一个连续的位图，我想把它们编码成一个光视频格式。我使用ffmpeg版本2.8.3（此处构建），在qt5、QTIDE和msvc2013下用于win32。

问题：我的代码在sws_scale（）处崩溃（有时在avcodec_encode_video2（）处崩溃）。当我浏览堆栈时，崩溃事件发生在sws_getCachedContext（）。（我只能看到这些ffmpeg构建的堆栈）。我只使用这些ffmpeg库（来自Qt.pro文件）：

LIBS += -lavcodec -lavformat -lswscale -lavutil

这是swscale哪个bug。这是代码：

void newVideo ()
{
    ULONG_PTR gdiplusToken;
    GdiplusStartupInput gdiplusStartupInput;
    GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
    initBitmap (); //init bmp
    int screenWidth =  bmp.bmiHeader.biWidth;
    int screenHeight = bmp.bmiHeader.biHeight;
    AVCodec * codec;
    AVCodecContext * c = NULL;
    uint8_t * outbuf;
    int i, out_size, outbuf_size;

    avcodec_register_all();
    qDebug () << "Video encodingn";
    // Find the mpeg1 video encoder
    codec = avcodec_find_encoder(AV_CODEC_ID_H264);
    if (!codec)
    {
        qDebug () << "Codec not foundn";
        avcodec_close(c);
        av_free(c);
        return;
    }
    else
        qDebug () << "H264 codec foundn";
    c = avcodec_alloc_context3(codec);
    c->bit_rate = 1000000;
    c->width = 800; // resolution must be a multiple of two (1280x720),(1900x1080),(720x480)
    c->height = 600;
    c->time_base.num = 1; // framerate numerator
    c->time_base.den = 25; // framerate denominator
    c->gop_size = 30; // emit one intra frame every ten frames
    c->max_b_frames = 1; // maximum number of b-frames between non b-frames
    c->pix_fmt = AV_PIX_FMT_YUV420P; //Converstion RGB to YUV ?
    c->codec_id = AV_CODEC_ID_H264;
    struct SwsContext* fooContext = sws_getContext(screenWidth, screenHeight,
                                                   AV_PIX_FMT_RGB32,
                                                   c->width, c->height,
                                                   AV_PIX_FMT_YUV420P,
                                                   SWS_FAST_BILINEAR,
                                                   NULL, NULL, NULL);
    // Open the encoder
    if (avcodec_open2(c, codec, NULL) < 0)
    {
        qDebug () << "Could not open codecn";
        avcodec_close(c);
        av_free(c);
        return;
    }
    else qDebug () << "H264 codec openedn";
    outbuf_size = 100000 + c->width*c->height*(32>>3);//*(32>>3); // alloc image and output buffer
    outbuf = static_cast<uint8_t *>(malloc(outbuf_size));
    qDebug() << "Setting buffer size to: " << outbuf_size << "n";
    FILE* f = fopen("TEST.mpg","wb");
    if(!f) qDebug() << "x - Cannot open video file for writingn";
    else qDebug() << "Opened video file for writingn";
    // encode 5 seconds of video
    for (i = 0; i < STREAM_FRAME_RATE*STREAM_DURATION; i++) //the stop condition i < 5.0*5
    {
        qDebug () << "i = " << i;
        fflush(stdout);
        HBITMAP hBmp;
        if (GetScreen(hBmp) == -1) return;
        BYTE * pPixels;// = new BYTE [bmp.bmiHeader.biSizeImage];
        pPixels = getPixels (hBmp);
        DeleteObject (hBmp);
        int nbytes = avpicture_get_size(AV_PIX_FMT_YUV420P, c->width, c->height);
        uint8_t* outbuffer = (uint8_t*)av_malloc(nbytes*sizeof(uint8_t));
        if(!outbuffer) // check if(outbuf) instead
        {
            qDebug () << "Bytes cannot be allocated";
            return;
        }
        AVFrame* inpic = avcodec_alloc_frame(); //av_frame_alloc () ?
        AVFrame* outpic = avcodec_alloc_frame();
        outpic->pts = (int64_t)((float)i * (1000.0/((float)(c->time_base.den))) * 90);
        if (avpicture_fill((AVPicture*) inpic, (uint8_t*) pPixels, AV_PIX_FMT_RGB32,
                       screenWidth, screenHeight) < 0)
            qDebug () <<  "avpicture_fill Fill picture with image failed"; //Fill picture with image
        if(avpicture_fill((AVPicture*) outpic, outbuffer, AV_PIX_FMT_YUV420P,
                       c->width, c->height) < 0)
            qDebug () <<  "avpicture_fill failed";
        if (av_image_alloc(outpic->data, outpic->linesize, c->width, c->height,
                       c->pix_fmt, 1) < 0)
            qDebug () <<  "av_image_alloc failed";
        inpic->data[0] += inpic->linesize[0]*(screenHeight - 1); // Flipping frame
        inpic->linesize[0] = -inpic->linesize[0]; // Flipping frame
////////////////////////////HERE THE BUG////////////////////////////////
        sws_scale(fooContext,
                  inpic->data, inpic->linesize,
                  0, c->height,
                  outpic->data, outpic->linesize); //HERE THE BUG
        av_free_packet((AVPacket *)outbuf);
        // encode the image
        out_size = avcodec_encode_video2 (c, (AVPacket *) outbuf,
                                          (AVFrame *) outbuf_size, (int *) outpic);
///////////////////////THE CODE DONT GO BEYOND/////////////////////////////////
        qDebug () << "Encoding frame" << i <<" (size=" << out_size <<"n";
        fwrite(outbuf, 1, out_size, f);
        delete [] pPixels;
        av_free(outbuffer);
        av_free(inpic);
        av_freep(outpic);
    }
    // get the delayed frames
    for(; out_size; i++)
    {
        fflush(stdout);
        out_size = avcodec_encode_video2 (c, (AVPacket *) outbuf,
                                          (AVFrame *) outbuf_size, NULL);
        qDebug () << "Writing frame" << i <<" (size=" << out_size <<"n";
        fwrite(outbuf, 1, out_size, f);
    }
    // add sequence end code to have a real mpeg file
    outbuf[0] = 0x00;
    outbuf[1] = 0x00;
    outbuf[2] = 0x01;
    outbuf[3] = 0xb7;
    fwrite(outbuf, 1, 4, f);
    fclose(f);
    avcodec_close(c);
    free(outbuf);
    av_free(c);
    qDebug () << "Closed codec and Freedn";
}

输出：

Video encoding
H264 codec found
H264 codec opened
Setting buffer size to:  2020000 
Opened video file for writing
i =  0
**CRASH**

我觉得我的位图不好，所以我制作了一个位图来测试，代码是：

    uint8_t* pPixels = new uint8_t[Width * 3 * Height];
    int x = 50;
    for(unsigned int i = 0; i < Width * 3 * Height; i = i + 3) // loop for generating color changing images
    {
        pPixels [i] = x % 255; //R
        pPixels [i + 1] = (x) % 255; //G
        pPixels [i + 2] = (255 - x) % 255; //B
    }

然而，崩溃仍在继续。也许，这可能会证明不是位图（pPixels）有问题。

如果有人知道的话，我为什么会出现这个错误：也许我没有很好地设置一个参数？还是一个ffmpeg弃用的函数？等

编辑1 2015年12月27日

由于Ronald S.Bultje函数sws_scale（）不会与此代码一起崩溃，但是我从中得到了一个错误糟糕的dst图像指针。我的代码：

//DESTINATION FRAME            
if (avpicture_alloc ((AVPicture*) dst_frame, AV_PIX_FMT_YUV420P, c->width, c->height) < 0)
            {
                qDebug () <<  "# avpicture_alloc failed";
                return;
            }
            if(avpicture_fill((AVPicture*) dst_frame, NULL, AV_PIX_FMT_YUV420P,
                           c->width, c->height) < 0)
                qDebug () <<  "avpicture_fill failed";
            avcodec_align_dimensions2 (c, &c->width, &c->height, dst_frame->linesize);
//SOURCE FRAME
            if (avpicture_fill((AVPicture*) src_frame, (uint8_t *) pPixels, AV_PIX_FMT_RGB32,
                               tmp_screenWidth, tmp_screenHeight) < 0)
                qDebug () <<  "# avpicture_fill Fill picture with image failed"; //Fill picture with image
            avcodec_align_dimensions2 (c, &tmp_screenWidth, &tmp_screenHeight, src_frame->linesize);
            struct SwsContext* conversionContext = sws_getContext(tmp_screenWidth,tmp_screenHeight,AV_PIX_FMT_RGB32,c->width, c->height, AV_PIX_FMT_YUV420P,SWS_FAST_BILINEAR, NULL, NULL, NULL);
            int output_Height = sws_scale(conversionContext,
                                          src_frame->data, src_frame->linesize,
                                          0, tmp_screenHeight,
                                          dst_frame->data, dst_frame->linesize); //return 0 -> bad dst image pointers error

编辑2 2015年12月28日

我试图遵循Ronald S.Bultje的建议，现在我得到了一个坏的src图像指针错误，我已经调查并工作了很多小时，但我没有找到解决方案。这里有一个新的片段：

AVFrame* src_frame = av_frame_alloc ();
AVFrame* dst_frame = av_frame_alloc ();
AVFrame* tmp_src_frame = av_frame_alloc ();
/*........I do not use them until this snippet..........*/
//DESTINATION
//avpicture_free ((AVPicture*)dst_frame);
avcodec_align_dimensions2 (c, &c->width, &c->height, dst_frame->linesize);
if (avpicture_alloc ((AVPicture*) dst_frame, AV_PIX_FMT_YUV420P, c->width, c->height) < 0)
{
    qDebug () <<  "# avpicture_alloc failed";
    return;
}
//SOURCE
//stride = src_frame->linesize [0] = ((((screenWidth * bitPerPixel) + 31) & ~31) >> 3); do I need to do that ?
//== stride - I have gotten this formula from : https://msdn.microsoft.com/en-us/library/windows/desktop/dd318229(v=vs.85).aspx
if (avpicture_fill((AVPicture*) src_frame, (uint8_t *) pPixels, AV_PIX_FMT_RGB32,
                   screenWidth, screenHeight) < 0)
    qDebug () <<  "# avpicture_fill Fill picture with image failed"; //Fill picture with image
//linesize [0] == 21760 like commented stride
//Source TO TMP Source
avcodec_align_dimensions2 (c, &tmp_screenWidth, &tmp_screenHeight, tmp_src_frame->linesize);
if (avpicture_fill((AVPicture*) tmp_src_frame, NULL, AV_PIX_FMT_RGB32,
                   tmp_screenWidth, tmp_screenHeight) < 0)
    qDebug () <<  "# avpicture_fill Fill picture with image failed"; //Fill picture with image
av_picture_copy ((AVPicture*) tmp_src_frame, (const AVPicture*) src_frame, AV_PIX_FMT_RGB32,
                 screenWidth, screenHeight);
struct SwsContext* conversionContext = sws_getContext(tmp_screenWidth, tmp_screenHeight,
                                                      AV_PIX_FMT_RGB32,
                                                      c->width, c->height,
                                                      AV_PIX_FMT_YUV420P,
                                                      SWS_FAST_BILINEAR,
                                                      NULL, NULL, NULL);
int output_Height = sws_scale(conversionContext,
                              tmp_src_frame->data, tmp_src_frame->linesize,
                              0, tmp_screenHeight,
                              dst_frame->data, dst_frame->linesize);
//ffmpeg error = bad src image pointers
// output_Height == 0

编辑3

对于临时图片，我已经完成了avcode_align_dimension2()，然后是用于分配内存的avpicture_alloc()和用于填充图片指针的avpicture_fill()。更新代码下方：

//DESTINATION
//avpicture_free ((AVPicture*)dst_frame);
avcodec_align_dimensions2 (c, &c->width, &c->height, dst_frame->linesize);
if (avpicture_alloc ((AVPicture*) dst_frame, AV_PIX_FMT_YUV420P, c->width, c->height) < 0)
{
    qDebug () <<  "# avpicture_alloc failed";
    return;
}
//SOURCE
//src_frame->linesize [0] = ((((screenWidth * bpp) + 31) & ~31) >> 3);
//src_frame->linesize [0] = stride;
if (avpicture_fill((AVPicture*) src_frame, (uint8_t *) pPixels, AV_PIX_FMT_RGB32,
                   screenWidth, screenHeight) < 0)
    qDebug () <<  "# avpicture_fill Fill picture with image failed"; //Fill picture with image
//Source TO TMP Source
avcodec_align_dimensions2 (c, &tmp_screenWidth, &tmp_screenHeight, tmp_src_frame->linesize);
if (avpicture_alloc ((AVPicture*) tmp_src_frame, AV_PIX_FMT_RGB32, tmp_screenWidth, tmp_screenHeight) < 0)
{
    qDebug () <<  "# avpicture_alloc failed";
    return;
}
int outbuf_size = tmp_screenWidth*tmp_screenHeight*4;// alloc image and output buffer
outbuf = static_cast<uint8_t *>(malloc(outbuf_size));
if (avpicture_fill((AVPicture*) tmp_src_frame, outbuf, AV_PIX_FMT_RGB32,
                   tmp_screenWidth, tmp_screenHeight) < 0)
    qDebug () <<  "# avpicture_fill Fill picture with image failed"; //Fill picture with image
av_picture_copy ((AVPicture*) tmp_src_frame, (const AVPicture*) src_frame, AV_PIX_FMT_RGB32,
                 tmp_screenWidth, tmp_screenHeight);
struct SwsContext* conversionContext = sws_getContext(tmp_screenWidth, tmp_screenHeight,
                                                      AV_PIX_FMT_RGB32,
                                                      c->width, c->height,
                                                      AV_PIX_FMT_YUV420P,
                                                      SWS_FAST_BILINEAR,
                                                      NULL, NULL, NULL);
int output_Height = sws_scale(conversionContext,
                              tmp_src_frame->data, tmp_src_frame->linesize,
                              0, tmp_screenHeight,
                              dst_frame->data, dst_frame->linesize);

调用堆栈如下：先调用av_picture_copy()，然后调用av_image_copy()，再调用_VEC_memcpy()，然后调用fastcopy_I()，然后崩溃。。。问题不在于尺寸（tmp_screenWidth/Height）？（使用av_picture_copy ()，我们可以将尺寸为W1xH1的图片P1复制到尺寸为W2xH2的图片P2吗？）

编辑4

在av_picture_copy()处崩溃，其中call _aligned_malloc()然后是av_image_copy _VEC_memcpy()和fastcopy_I()

//SOURCE
if (avpicture_fill((AVPicture*) src_frame, (uint8_t *) pPixels, AV_PIX_FMT_RGB32,
                   screenWidth, screenHeight) < 0)
    qDebug () <<  "# avpicture_fill Fill picture with image failed"; //Fill picture with image
//Source TO TMP Source
avcodec_align_dimensions2 (c, &tmp_screenWidth, &tmp_screenHeight, tmp_src_frame->linesize);
if (avpicture_alloc ((AVPicture*) tmp_src_frame, AV_PIX_FMT_RGB32, tmp_screenWidth, tmp_screenHeight) < 0)
{
    qDebug () <<  "# avpicture_alloc failed";
    return;
}
av_picture_copy ((AVPicture*) tmp_src_frame, (const AVPicture*) src_frame, AV_PIX_FMT_RGB32,
                 tmp_screenWidth, tmp_screenHeight);

您使用的是avpicture_fill（），其实现方式如下：

int avpicture_fill(AVPicture *picture, const uint8_t *ptr,
                   enum AVPixelFormat pix_fmt, int width, int height)
{
    return av_image_fill_arrays(picture->data, picture->linesize,
                                ptr, pix_fmt, width, height, 1);
}

注意av_image_fill_arrays（）的最后一个参数，align=1。这意味着缓冲区行将不对齐。不幸的是，这一点在文档中根本不清楚，大多数FFmpeg函数都需要将缓冲线对齐为2的幂，以允许SSE2或AVX2优化，例如align=32。请参阅此响应中关于如何以编程方式执行此操作的第二个要点。

此外，在测试代码中，您使用new（而不是av_malloc）来分配内存，并且new返回的指针也不能保证按32字节对齐。

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