#include <iostream> using namespace std; extern "C" { #include "libavcodec/avcodec.h" #include "libavformat/avformat.h" #include "libswscale/swscale.h" #include "libavutil/imgutils.h" } int savePicture(AVFrame *pFrame, char *out_name) ; int main(int argc, char *argv[]) {//解码视频 int ret; const char *in_filename, *out_filename; AVFormatContext *fmt_ctx = NULL; const AVCodec *codec; AVCodecContext *codeCtx = NULL; AVStream *stream = NULL; int stream_index; AVPacket avpkt; int frame_count; AVFrame *frame; if (argc <= 2) { printf("Usage: %s <input file> <output file>\n", argv[0]); exit(0); } in_filename = argv[1]; out_filename = argv[2]; // 1 if (avformat_open_input(&fmt_ctx, in_filename, NULL, NULL) < 0) { printf("Could not open source file %s\n", in_filename); exit(1); } if (avformat_find_stream_info(fmt_ctx, NULL) < 0) { printf("Could not find stream information\n"); exit(1); } av_dump_format(fmt_ctx, 0, in_filename, 0); av_init_packet(&avpkt); //初始化AVPacket,只是单纯初始化avpkt字段 avpkt.data = NULL; avpkt.size = 0; // 2 stream_index = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0); if (ret < 0) { fprintf(stderr, "Could not find %s stream in input file '%s'\n", av_get_media_type_string(AVMEDIA_TYPE_VIDEO), in_filename); return ret; } stream = fmt_ctx->streams[stream_index]; // 3 codec = avcodec_find_decoder(stream->codecpar->codec_id); //查找指定的解码器 if (codec == NULL) { return -1; } // 4 codeCtx = avcodec_alloc_context3(NULL); //分配解码器上下文 if (!codeCtx) { fprintf(stderr, "Could not allocate video codec context\n"); exit(1); } // 5 if ((ret = avcodec_parameters_to_context(codeCtx, stream->codecpar)) < 0) { //将AVCodecParameters对象转为AVCodecContext对象 fprintf(stderr, "Failed to copy %s codec parameters to decoder context\n", av_get_media_type_string(AVMEDIA_TYPE_VIDEO)); return ret; } // 6 avcodec_open2(codeCtx, codec, NULL); //打开解码器和关联解码器上下文 //初始化frame，解码后数据 frame = av_frame_alloc(); if (!frame) { fprintf(stderr, "Could not allocate video frame\n"); exit(1); } frame_count = 0; char buf[1024]; // 7 while (av_read_frame(fmt_ctx, &avpkt) >= 0) { if (avpkt.stream_index == stream_index) { // 8 int re = avcodec_send_packet(codeCtx, &avpkt); //发送给解码器 if (re < 0) { continue; } // 9 这里必须用while()，因为一次avcodec_receive_frame可能无法接收到所有数据 while (avcodec_receive_frame(codeCtx, frame) == 0) { //接收解码后的帧 // 拼接图片路径、名称 snprintf(buf, sizeof(buf), "%s/picture-%d.jpg", out_filename, frame_count); //将 out_filename/picture-frame_count.jpg 复制到buf savePicture(frame, buf); //保存为jpg图片 } frame_count++; } av_packet_unref(&avpkt); } } int savePicture(AVFrame *pFrame, char *out_name) {//编码保存图片 int width = pFrame->width; int height = pFrame->height; AVCodecContext *pCodeCtx = NULL; AVFormatContext *pFormatCtx = avformat_alloc_context(); // 设置输出文件格式 pFormatCtx->oformat = av_guess_format("mjpeg", NULL, NULL); // 创建并初始化输出AVIOContext if (avio_open(&pFormatCtx->pb, out_name, AVIO_FLAG_READ_WRITE) < 0) { printf("Couldn't open output file."); return -1; } // 构建一个新stream AVStream *pAVStream = avformat_new_stream(pFormatCtx, 0); if (pAVStream == NULL) { return -1; } AVCodecParameters *parameters = pAVStream->codecpar; parameters->codec_id = pFormatCtx->oformat->video_codec; parameters->codec_type = AVMEDIA_TYPE_VIDEO; parameters->format = AV_PIX_FMT_YUVJ420P; parameters->width = pFrame->width; parameters->height = pFrame->height; AVCodec *pCodec = avcodec_find_encoder(pAVStream->codecpar->codec_id); //查找编码器 if (!pCodec) { printf("Could not find encoder\n"); return -1; } pCodeCtx = avcodec_alloc_context3(pCodec); //为AVCodecContext分配内存 if (!pCodeCtx) { fprintf(stderr, "Could not allocate video codec context\n"); exit(1); } if ((avcodec_parameters_to_context(pCodeCtx, pAVStream->codecpar)) < 0) { fprintf(stderr, "Failed to copy %s codec parameters to decoder context\n", av_get_media_type_string(AVMEDIA_TYPE_VIDEO)); return -1; } pCodeCtx->time_base = (AVRational) {1, 25}; if (avcodec_open2(pCodeCtx, pCodec, NULL) < 0) { //打开编码器 printf("Could not open codec."); return -1; } int ret = avformat_write_header(pFormatCtx, NULL); if (ret < 0) { printf("write_header fail\n"); return -1; } int y_size = width * height; //Encode // 给AVPacket分配足够大的空间 AVPacket pkt; av_new_packet(&pkt, y_size * 3); // 编码数据 ret = avcodec_send_frame(pCodeCtx, pFrame); if (ret < 0) { printf("Could not avcodec_send_frame."); return -1; } // 得到编码后数据 ret = avcodec_receive_packet(pCodeCtx, &pkt); if (ret < 0) { printf("Could not avcodec_receive_packet"); return -1; } ret = av_write_frame(pFormatCtx, &pkt); if (ret < 0) { printf("Could not av_write_frame"); return -1; } av_packet_unref(&pkt); //Write Trailer av_write_trailer(pFormatCtx); avcodec_close(pCodeCtx); avio_close(pFormatCtx->pb); avformat_free_context(pFormatCtx); return 0; }
标签：一帧,stream,frame,jpeg,codec,av,NULL,avcodec,FFmpeg From： https://www.cnblogs.com/lidabo/p/17648868.html