ffmpeg保存为jpg文件

int img_savePicture(AVFrame *pFrame, char *out_filename) {//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_filename, 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);

if (!pCodec) {
printf("Could not find encoder ");
return -1;
}

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

if ((avcodec_parameters_to_context(pCodeCtx, pAVStream->codecpar)) < 0) {
fprintf(stderr, "Failed to copy %s codec parameters to decoder context ",
av_get_media_type_string(AVMEDIA_TYPE_VIDEO));
return -1;
}
AVRational Rat;
Rat.num =1;
Rat.den =25;
pCodeCtx->time_base = Rat;

if (avcodec_open2(pCodeCtx, pCodec, NULL) < 0) {
printf("Could not open codec.");
return -1;
}

int ret = avformat_write_header(pFormatCtx, NULL);
if (ret < 0) {
printf("write_header fail ");
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;

}