c++ - 编码 H.264 时 avcodec_encode_video2() 出现段错误

Question

我正在尝试将 cv::Mat 转换为 AVFrame 以在 H.264 中对其进行编码，我想从一个简单的示例开始，因为我两者都是新手。所以我首先读入一个 JPEG 文件，然后使用 sws_scale() 将像素格式从 AV_PIX_FMT_BGR24 转换为 AV_PIX_FMT_YUV420P，保持尺寸不变，在我调用 avcodec_encode_video2() 之前一切正常。

我阅读了很多关于 AVFrame 分配和问题 Segmentation fault while avcodec_encode_video2 的讨论。看起来很匹配，但我看不出我遗漏了什么或错了什么。

这是您可以重现崩溃的最少代码，应该使用它进行编译，

g++ -o OpenCV2FFmpeg OpenCV2FFmpeg.cpp -lopencv_imgproc -lopencv_highgui -lopencv_core -lswscale -lavutil -lavcodec -lavformat

这是我系统的输出，

cv::Mat [width=420, height=315, depth=0, channels=3, step=1260]
I'll soon crash..
Segmentation fault

sample.jpg 文件的详细信息由 identify 工具，

~temporary/sample.jpg JPEG 420x315 420x315+0+0 8-bit sRGB 38.3KB 0.000u 0:00.000

请注意，为了简单起见，我正在尝试用单张图片制作视频。

#include <iostream>
#include <cassert>
using namespace std;

extern "C" {
    #include <libavcodec/avcodec.h>
    #include <libswscale/swscale.h>
    #include <libavformat/avformat.h>
}

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>

const string TEST_IMAGE = "/home/baris/temporary/sample.jpg";

int main(int /*argc*/, char** argv)
{
    av_register_all();
    avcodec_register_all();

    /**
     * Initialise the encoder
     */
    AVCodec *h264encoder = avcodec_find_encoder(AV_CODEC_ID_H264);
    AVFormatContext *cv2avFormatContext = avformat_alloc_context();

    /**
     * Create a stream and allocate frames
     */
    AVStream *h264outputstream = avformat_new_stream(cv2avFormatContext, h264encoder);
    avcodec_get_context_defaults3(h264outputstream->codec, h264encoder);
    AVFrame *sourceAvFrame = av_frame_alloc(), *destAvFrame = av_frame_alloc();
    int got_frame;

    /**
     * Pixel formats for the input and the output
     */
    AVPixelFormat sourcePixelFormat = AV_PIX_FMT_BGR24;
    AVPixelFormat destPixelFormat = AV_PIX_FMT_YUV420P;

    /**
     * Create cv::Mat
     */
    cv::Mat cvFrame = cv::imread(TEST_IMAGE, CV_LOAD_IMAGE_COLOR);
    int width = cvFrame.size().width, height = cvFrame.size().height;
    cerr << "cv::Mat [width=" << width << ", height=" << height << ", depth=" << cvFrame.depth() << ", channels=" << cvFrame.channels() << ", step=" << cvFrame.step << "]" << endl;

    h264outputstream->codec->pix_fmt = destPixelFormat;
    h264outputstream->codec->width = cvFrame.cols;
    h264outputstream->codec->height = cvFrame.rows;

    /**
     * Prepare the conversion context
     */
    SwsContext *bgr2yuvcontext = sws_getContext(width, height,
                                                sourcePixelFormat,
                                                h264outputstream->codec->width, h264outputstream->codec->height,
                                                h264outputstream->codec->pix_fmt,
                                                SWS_BICUBIC, NULL, NULL, NULL);

    /**
     * Convert and encode frames
     */
    for (uint i=0; i < 250; i++)
    {
        /**
         * Allocate source frame, i.e. input to sws_scale()
         */
        avpicture_alloc((AVPicture*)sourceAvFrame, sourcePixelFormat, width, height);

        for (int h = 0; h < height; h++)
            memcpy(&(sourceAvFrame->data[0][h*sourceAvFrame->linesize[0]]), &(cvFrame.data[h*cvFrame.step]), width*3);

        /**
         * Allocate destination frame, i.e. output from sws_scale()
         */
        avpicture_alloc((AVPicture *)destAvFrame, destPixelFormat, width, height);

        sws_scale(bgr2yuvcontext, sourceAvFrame->data, sourceAvFrame->linesize,
                  0, height, destAvFrame->data, destAvFrame->linesize);

        /**
         * Prepare an AVPacket for encoded output
         */
        AVPacket avEncodedPacket;
        av_init_packet(&avEncodedPacket);
        avEncodedPacket.data = NULL;
        avEncodedPacket.size = 0;
        // av_free_packet(&avEncodedPacket); w/ or w/o result doesn't change

        cerr << "I'll soon crash.." << endl;
        if (avcodec_encode_video2(h264outputstream->codec, &avEncodedPacket, destAvFrame, &got_frame) < 0)
            exit(1);

        cerr << "Checking if we have a frame" << endl;
        if (got_frame)
            av_write_frame(cv2avFormatContext, &avEncodedPacket);

        av_free_packet(&avEncodedPacket);
        av_frame_free(&sourceAvFrame);
        av_frame_free(&destAvFrame);
    }
}

提前致谢!

编辑: 崩溃后的堆栈跟踪，

Thread 2 (Thread 0x7fffe5506700 (LWP 10005)):
#0  0x00007ffff4bf6c5d in poll () at /lib64/libc.so.6
#1  0x00007fffe9073268 in  () at /usr/lib64/libusb-1.0.so.0
#2  0x00007ffff47010a4 in start_thread () at /lib64/libpthread.so.0
#3  0x00007ffff4bff08d in clone () at /lib64/libc.so.6

Thread 1 (Thread 0x7ffff7f869c0 (LWP 10001)):
#0  0x00007ffff5ecc7dc in avcodec_encode_video2 () at /usr/lib64/libavcodec.so.56
#1  0x00000000004019b6 in main(int, char**) (argv=0x7fffffffd3d8) at ../src/OpenCV2FFmpeg.cpp:99

EDIT2:问题是我没有avcodec_open2() Ronald 发现的编解码器。代码的最终版本位于 https://github.com/barisdemiray/opencv2ffmpeg/ ，有泄漏，可能还有其他问题，希望我能在学习这两个库的同时改进它。

Answer 1

请提供崩溃后的 gdb 回溯。我很确定它会崩溃，因为您的图片指针未对齐(avpicture_alloc() 将分配未对齐的图像，而 avcodec_encode_video2() 需要对齐的数据指针)，但可能还有其他原因会导致它崩溃。

要对齐 AVFrame 中的数据指针，请使用 av_image_alloc()和相关函数，align=32。

另一个问题是你没有调用 avcodec_open2 (h264outputstream->codec, h264encoder).