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

我正在尝试将cv::Mat转换为AVFrame，然后在H.264中对其进行编码，并希望从一个简单的示例开始，因为我都是这方面的新手。因此，我首先读取一个JPEG文件，然后使用sws_scale()从AV_PIX_FMT_BGR24到AV_PIX_FMT_YUV420P进行像素格式转换，并保持尺寸不变，并且一切正常，直到我调用avcodec_encode_video2()为止。

我阅读了许多有关AVFrame分配的讨论，而Segmentation fault while avcodec_encode_video2问题似乎很匹配，但我只是看不到我所缺少或出错的地方。

这是您可以重现崩溃的最小代码，应使用该代码进行编译，

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

它是在我的系统上输出的

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

并通过sample.jpg工具查看identify文件的详细信息，

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

请注意，我试图从单个图像创建视频，只是为了使事情简单。

#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

编辑2:问题是我没有像Ronald所发现的那样对编解码器进行avcodec_open2()编码。该代码的最终版本位于https://github.com/barisdemiray/opencv2ffmpeg/，存在泄漏和可能还有其他问题，希望我在学习这两个库的同时加以改进。

最佳答案

请在崩溃后提供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()期望对齐的数据指针)，但是可能还会有其他原因使其崩溃。

要在AVFrame中对齐数据指针，请使用av_image_alloc()和相关函数(align = 32)。

另一个问题是您没有调用avcodec_open2(h264outputstream-> codec，h264encoder)。