ubuntu编译FFmpeg并使用编译好的so使用c++进行编码和解码

得到一个安卓系统中，编码和解码要跑在native层的需求。目前我的计划是分两步走：
1.那么需要使用NDK交叉编译FFmpeg获得对应平台的so
2.打算在ubuntu下先写好对应的sample code，测试完成后，将头文件和cpp文件直接编译成so给安卓侧使用。

根据第2点，需要编译X86平台下的FFmpeg的so。
以下记录一下在X86平台下编译遇到的问题
1.下载ffmpeg源码，可以从github上下载，也可以从官网下载，我这边直接从github中下载最新的源码。
https://github.com/FFmpeg/FFmpeg

2.因为我要编译一个可以encode和decode的so,所以还需要下载一个libx264，
下载地址 https://www.videolan.org/developers/x264.html
下载完后cd进到x264的文件夹中执行以下命令。

./configure --prefix=/home/wei/ffmpeg --enable-shared --disable-asm
sudo make -j8
sudo make install

其中 --prefix是这个x264编译好后存放的地址，我是放到了/home/wei/ffmpeg中，编译完后会在/home/wei/ffmpeg生成include和lib文件夹，会将对应的头文件和so放到对应的文件夹中。
如果需要安装其他功能模块的，可以参考这篇博客，
https://blog.csdn.net/yellowyz/article/details/134547483。

3.编译好libx264和，cd到FFmpeg文件夹中，因为我是要生成动态链接库，已经有编码和解码的功能，可以执行以下脚本。

./configure --prefix="/home/wei/WorkShape/ffmpeg" \
--enable-gpl \
--enable-nonfree \
--enable-shared \
--enable-libmp3lame \
--enable-libx264 \
--enable-decoder=h264 \
--enable-filter=delogo \
--enable-debug \
--disable-optimizations \
--enable-libspeex \


make -j8
sudo make install

其实脚本中间也有没有用的模块，不过我偷懒就没有删除，区别就是可能编译的时间久一点，但是最基本的编码和解码时有了，其他要打开的功能可以自己参考以上写法即可。–enable-libx264 打开编码，–enable-decoder=h264打开解码，–enable-shared生成动态链接库。

最后根据我的编译选项，在/home/wei/ffmpeg/inlucde中会生成以下文件夹

在，在/home/wei/ffmpeg/lib中会生成以下动态库，可以后续给自己的程序链接上。

编译好链接库后，可以正式的写测试代码了，以下代码是我从ffmpeg/doc/example下拿到的，进行了适当的修改，打开一张nv12的图片，然后拷贝到frame中，进行编码。需要修改的就是 const char *inputFile = “1280_1024.nv12”; 文件的名称，和你图片的宽高即可。运行后会生成一个test.mp4。
#define image_width 1280
#define image_height 1024

编码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

extern "C"
{
#include <libavcodec/avcodec.h>
#include <libavutil/opt.h>
#include <libavutil/imgutils.h>
    // #include <libavutil/error.h>
}

#define image_width 1280
#define image_height 1024
static void encode(AVCodecContext *enc_ctx, AVFrame *frame, AVPacket *pkt,
                   FILE *outfile)
{
    int ret;

    /* send the frame to the encoder */
    if (frame)
        printf("Send frame %3" PRId64 "\n", frame->pts);

    ret = avcodec_send_frame(enc_ctx, frame);
    if (ret < 0)
    {
        fprintf(stderr, "Error sending a frame for encoding\n");
        exit(1);
    }

    while (ret >= 0)
    {
        ret = avcodec_receive_packet(enc_ctx, pkt);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
            return;
        else if (ret < 0)
        {
            fprintf(stderr, "Error during encoding\n");
            exit(1);
        }

        printf("Write packet %3" PRId64 " (size=%5d)\n", pkt->pts, pkt->size);
        fwrite(pkt->data, 1, pkt->size, outfile);
        av_packet_unref(pkt);
    }
}

int main(int argc, char **argv)
{
    const char *filename = "test.mp4", *codec_name = "libx264";
    const AVCodec *codec;
    AVCodecContext *c = NULL;
    int i, ret, x, y;
    FILE *f;

    AVFrame *frame;
    AVPacket *pkt;
    uint8_t endcode[] = {0, 0, 1, 0xb7};



    /* find the mpeg1video encoder */
    codec = avcodec_find_encoder_by_name(codec_name);
    if (!codec)
    {
        fprintf(stderr, "Codec '%s' not found\n", codec_name);
        exit(1);
    }

    c = avcodec_alloc_context3(codec);
    if (!c)
    {
        fprintf(stderr, "Could not allocate video codec context\n");
        exit(1);
    }

    pkt = av_packet_alloc();
    if (!pkt)
        exit(1);

    /* put sample parameters */
    c->bit_rate = 400000;
    /* resolution must be a multiple of two */
    c->width = 1280;
    c->height = 1024;
    /* frames per second */
    c->time_base = (AVRational){1, 25};
    c->framerate = (AVRational){25, 1};

    /* emit one intra frame every ten frames
     * check frame pict_type before passing frame
     * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
     * then gop_size is ignored and the output of encoder
     * will always be I frame irrespective to gop_size
     */
    c->gop_size = 10;
    c->max_b_frames = 1;
    c->pix_fmt = AV_PIX_FMT_NV12;

    if (codec->id == AV_CODEC_ID_H264)
        av_opt_set(c->priv_data, "preset", "slow", 0);

    /* open it */
    ret = avcodec_open2(c, codec, NULL);
    if (ret < 0)
    {
        fprintf(stderr, "Could not open codec: \n");
        exit(1);
    }
    f = fopen(filename, "wb");
    if (!f)
    {
        fprintf(stderr, "Could not open %s\n", filename);
        exit(1);
    }

    const char *inputFile = "1280_1024.nv12";
    uint8_t *buffer = (uint8_t *)malloc(image_width * image_height * 3 / 2);
    FILE *file = fopen(inputFile, "rb");
    if (file == nullptr)
    {
        printf("无法打开文件 %s\n", inputFile);
        return 0;
    }
    fread(buffer, 1, image_width * image_height * 3 / 2, file);
    fclose(file);

    frame = av_frame_alloc();
    if (!frame)
    {
        fprintf(stderr, "Could not allocate video frame\n");
        exit(1);
    }
    frame->format = c->pix_fmt;
    frame->width = c->width;
    frame->height = c->height;

    ret = av_frame_get_buffer(frame, 0);
    if (ret < 0)
    {
        fprintf(stderr, "Could not allocate the video frame data\n");
        exit(1);
    }
    memcpy(frame->data[0], buffer, image_width * image_height);
    memcpy(frame->data[1], buffer + image_width * image_height, image_width * image_height / 2);

    
    for (i = 0; i < 25; i++)
    {
        fflush(stdout);

        /* Make sure the frame data is writable.
           On the first round, the frame is fresh from av_frame_get_buffer()
           and therefore we know it is writable.
           But on the next rounds, encode() will have called
           avcodec_send_frame(), and the codec may have kept a reference to
           the frame in its internal structures, that makes the frame
           unwritable.
           av_frame_make_writable() checks that and allocates a new buffer
           for the frame only if necessary.
         */
        ret = av_frame_make_writable(frame);
        if (ret < 0)
            exit(1);

        /* Prepare a dummy image.
           In real code, this is where you would have your own logic for
           filling the frame. FFmpeg does not care what you put in the
           frame.
         */
        /* Y */

        // for (y = 0; y < c->height; y++)
        // {
        //     for (x = 0; x < c->width; x++)
        //     {
        //         frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
        //     }
        // }

        // /* Cb and Cr */
        // for (y = 0; y < c->height / 2; y++)
        // {
        //     for (x = 0; x < c->width / 2; x++)
        //     {
        //         frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
        //         frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
        //     }
        // }
        frame->pts = i;

        /* encode the image */
        encode(c, frame, pkt, f);
    }

    /* flush the encoder */
    encode(c, NULL, pkt, f);

    /* Add sequence end code to have a real MPEG file.
       It makes only sense because this tiny examples writes packets
       directly. This is called "elementary stream" and only works for some
       codecs. To create a valid file, you usually need to write packets
       into a proper file format or protocol; see mux.c.
     */
    if (codec->id == AV_CODEC_ID_MPEG1VIDEO || codec->id == AV_CODEC_ID_MPEG2VIDEO)
        fwrite(endcode, 1, sizeof(endcode), f);
    fclose(f);

    avcodec_free_context(&c);
    av_frame_free(&frame);
    av_packet_free(&pkt);

    return 0;
}

解码

接着开始写解码的过程，将刚才编码生成的mp4 解码成yuv 的数据

#include <stdexcept>
#include <iostream>
#include <memory>
#include <mutex>
extern "C"
{
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
}

class VideoDecoder
{
private:
    AVFormatContext *formatContext;
    AVCodecContext *codecContext;
    const AVCodec *codec;
    int videoStreamIndex;
    AVFrame *frame;
    // ASVLOFFSCREEN DstImg;
    std::mutex data_mutex_;
    const char *inputFilePath;
    bool exit_;
    bool video_decoded_;
    int H264_frame;
    bool isFirstFrameReady;

public:
    VideoDecoder();
    ~VideoDecoder();
    void init(const char *input);
    int decode(char *display_buffer);
    void set_thread_exit();
    bool get_video_decoded_();
    bool getIsFirstFrameReady();

};

#include "VideoDecoder.h"

VideoDecoder::VideoDecoder() : formatContext(nullptr),
                               codecContext(nullptr),
                               codec(nullptr),
                               videoStreamIndex(-1),
                               exit_(false),
                               video_decoded_(false),
                               H264_frame(0),
                               isFirstFrameReady(false)
{
    frame = av_frame_alloc();
}

VideoDecoder::~VideoDecoder()
{

    if (&frame)
    {
        av_frame_free(&frame);
    }
    avcodec_free_context(&codecContext);
    avformat_close_input(&formatContext);
}


void VideoDecoder::init(const char *input)
{
    inputFilePath = input;
    if (avformat_open_input(&formatContext, inputFilePath, nullptr, nullptr) != 0)
    {
        throw std::runtime_error("无法打开视频文件");
    }

    if (avformat_find_stream_info(formatContext, nullptr) < 0)
    {
        throw std::runtime_error("无法获取视频流信息");
    }

    for (unsigned int i = 0; i < formatContext->nb_streams; i++)
    {
        if (formatContext->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            videoStreamIndex = i;
            break;
        }
    }

    if (videoStreamIndex == -1)
    {
        throw std::runtime_error("无法找到视频流");
    }

    AVCodecParameters *codecParams = formatContext->streams[videoStreamIndex]->codecpar;

    codec = avcodec_find_decoder(codecParams->codec_id);
    if (!codec)
    {
        throw std::runtime_error("无法找到视频解码器");
    }

    codecContext = avcodec_alloc_context3(codec);
    if (!codecContext)
    {
        throw std::runtime_error("无法创建解码器上下文");
    }

    if (avcodec_parameters_to_context(codecContext, codecParams) < 0)
    {
        throw std::runtime_error("无法初始化解码器上下文");
    }

    if (avcodec_open2(codecContext, codec, nullptr) < 0)
    {
        throw std::runtime_error("无法打开解码器");
    }
}

bool VideoDecoder::get_video_decoded_()
{
    std::unique_lock<std::mutex> lock(data_mutex_);
    return video_decoded_;
}

bool VideoDecoder::getIsFirstFrameReady()
{
    std::unique_lock<std::mutex> lock(data_mutex_);
    return isFirstFrameReady;
}

void VideoDecoder::set_thread_exit()
{
    exit_ = true;
}
int VideoDecoder::decode(char *display_buffer)
{
    try
    {
        AVPacket packet;
        video_decoded_ = false;
        while (av_read_frame(formatContext, &packet) >= 0)
        {
            if (exit_)
            {
                printf("exit_:%d\n", exit_);
                break;
            }
            if (packet.stream_index == videoStreamIndex)
            {
                avcodec_send_packet(codecContext, &packet);
                int ret = avcodec_receive_frame(codecContext, frame);
                if (ret == 0)
                {
                    std::unique_lock<std::mutex> lock(data_mutex_);
                    {
                      
                        // 假设帧的格式是AV_PIX_FMT_YUV420P
                        FILE *file = fopen(("frame" + std::to_string(H264_frame) + ".yuv").c_str(), "wb");

                        if (file != nullptr)
                        {
                            // 写入Y分量
                            fwrite(frame->data[0], 1, frame->linesize[0] * frame->height, file);
                            // 写入U分量
                            fwrite(frame->data[1], 1, frame->linesize[1] * frame->height / 2, file);
                            // 写入V分量
                            fwrite(frame->data[2], 1, frame->linesize[2] * frame->height / 2, file);

                            fclose(file);
                        }
                    }
                }
            }
            av_packet_unref(&packet);
            printf("filename :%s  H264_frame%d\n", inputFilePath, H264_frame);
            H264_frame++;
        }
        printf("filename :%s decode finished\n", inputFilePath);
        std::unique_lock<std::mutex> lock(data_mutex_);
        video_decoded_ = true;
    }
    catch (const std::exception &ex)
    {
        std::cerr << "Error: " << ex.what() << std::endl;
    }
    return 0;
}

#include "VideoDecoder.h"
#include <iostream>
extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/imgutils.h"
#include "libavutil/avassert.h"
#include "libswscale/swscale.h"
}

int main()
{
    char *display_buffer = (char *)malloc(1280 * 1024 * 3 / 2);
    const char *filename = "test.mp4";
    VideoDecoder videoDecoder;
    videoDecoder.init(filename);
    videoDecoder.decode(display_buffer);
    return 0;
}

以上是解码的头文件和cpp 文件，以及main 函数，自己通过cmakelists.txt进行链接编译即可。