最简单的音视频解封装器,基于FFmpeg4.1实现(一)

最简单的音视频解封装器,基于FFmpeg4.1实现

最近在学习FFmpeg，打算照着FFmpeg官方文档和官方的examples实现一些程序，加深理解，首先先实现一个解封装的程序。代码运行效果如下图：
代码的注释写的很详细，环境是在vs2019中运行的，下面直接上代码：

#include
#include
extern "C"
{
#include
}
int main(int argc,char *argv[])
{const char* videoname = NULL;/*if (argc!=1) {std::cout <<"when you run ,the video name should be entered!" <videoname = "test1.mp4";/* 通过avformat_open_input()打开文件并且为acformatcontext分配空间*/AVFormatContext* fmt_ctx = NULL;/**第三个参数，是媒体格式，置空则会自动探测。第四个参数， it is not possible to set demuxer private options on a preallocatedcontext. Instead, the options should be passed to avformat_open_input()wrapped in an AVDictionary:*/if (avformat_open_input(&fmt_ctx, videoname, NULL, NULL) < 0) {std::cout << "could not open soure file :" << videoname << std::endl;return -1;};/**Read packets of a media file to get stream information.This is useful for file formats with no headers such as MPEG. This function also computes the real framerate in case of MPEG-2 repeat frame mode. The logical file position is not changed by this function; examined packets may be buffered for later processing.*/if (avformat_find_stream_info(fmt_ctx, NULL) < 0) {std::cout << "could not find stream information."<< std::endl;return -1;}//查找码流int videostream = -1;int audiostream = -1;int subtitlestream = -1;videostream=av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);if (videostream<0) {std::cout << "could not find video stream information." << std::endl;}audiostream = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);if (audiostream<0) {std::cout << "could not find audio stream information." << std::endl;}//字幕流subtitlestream = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_SUBTITLE, -1, -1, NULL, 0);if (subtitlestream<0) {std::cout << "could not find subtitle stream information." << std::endl;}//打印信息std::cout << "--------------------------视频流-------------------------" << std::endl;std::cout << "索引号:" << videostream << " " << " 解码器ID：" << fmt_ctx->streams[videostream]->codecpar->codec_id<< "视频宽*高" << fmt_ctx->streams[videostream]->codecpar->width << "*" << fmt_ctx->streams[videostream]->codecpar->height << std::endl;std::cout << "--------------------------音频流-------------------------" << std::endl;std::cout << "索引号:" << audiostream << " " << " 解码器ID：" << fmt_ctx->streams[audiostream]->codecpar->codec_id<< "音频声道数：" << fmt_ctx->streams[audiostream]->codecpar->channels << std::endl;std::cout << "--------------------------字幕流-------------------------" << std::endl;AVPacket *pkt=NULL;//av_init_packet(pkt);pkt = av_packet_alloc();for (;;){if (av_read_frame(fmt_ctx, pkt) < 0){std::cout << "读到文件结尾了！" << std::endl;break;};if (pkt->stream_index == videostream){//打印信息std::cout << "--------------------------视频流-------------------------" << std::endl;std::cout <<"duration: " << pkt->duration * (double)((double)fmt_ctx->streams[1]->time_base.num / (double)fmt_ctx->streams[1]->time_base.den)*1000 <<"ms"<< std::endl;;std::cout << "size: " << pkt->size << std::endl;std::cout << "pts : " << pkt->pts * (double)((double)fmt_ctx->streams[1]->time_base.num / (double)fmt_ctx->streams[1]->time_base.den) * 1000 << "ms" <<" dts :"<< pkt->dts * (double)((double)fmt_ctx->streams[1]->time_base.num / (double)fmt_ctx->streams[1]->time_base.den) * 1000 << "ms" <<std::endl;}if (pkt->stream_index == audiostream){//打印信息std::cout << "--------------------------音频流-------------------------" << std::endl;std::cout <<"duration: " << pkt->duration * (double)((double)fmt_ctx->streams[1]->time_base.num / (double)fmt_ctx->streams[1]->time_base.den) * 1000 << "ms" << std::endl;;std::cout << "size: " << pkt->size << std::endl;std::cout << "pts : " << pkt->pts * (double)((double)fmt_ctx->streams[1]->time_base.num / (double)fmt_ctx->streams[1]->time_base.den) * 1000 << "ms"<< " dts :" << pkt->dts * (double)((double)fmt_ctx->streams[1]->time_base.num / (double)fmt_ctx->streams[1]->time_base.den) * 1000 << "ms" << std::endl;}//每次调用av_read_frame会导致pkt的引用计数加1，要即时清理。//否则会导致内存泄漏av_packet_unref(pkt);}av_packet_free(&pkt);avformat_close_input(&fmt_ctx);return 0;
}


这部分程序可能存在内存泄漏的地方只有一个，就是AVPacket对象在申请完内存后，记得在av_read_frame()循环中对引用技术减1，即av_packet_unref(pkt);

参考：
[1]: 100行代码实现最简单的基于FFMPEG+SDL的视频播放器（SDL1.x）