整个我的项目在 https://github.com/ximikang/ffmpegThumbnail 公布
生成缩略图的步骤
- 应用 ffmpeg 解码视频
- 帧格局转换
- 依据缩略图的数量从视频流中取帧
- 应用 opencv 建设画布并生成缩略图
ffmpeg 解码视频
依据缩略图的数量从视频流中取帧
- 获取图片之间的工夫距离
// Read media file and read the header information from container format
AVFormatContext* pFormatContext = avformat_alloc_context();
if (!pFormatContext) {logging("ERROR could not allocate memory for format context");
return -1;
}
if (avformat_open_input(&pFormatContext, inputFilePath.string().c_str(), NULL, NULL) != 0) {logging("ERROR could not open media file");
}
logging("format %s, duration %lld us, bit_rate %lld", pFormatContext->iformat->name, pFormatContext->duration, pFormatContext->bit_rate);
cout << "视频时常:" << pFormatContext->duration / 1000.0 / 1000.0 << "s" << endl;
int64_t video_duration = pFormatContext->duration;
int sum_count = rowNums * colNums;
// 跳转的距离 ms
int64_t time_step = video_duration / sum_count / 1000;
- 设置跳转工夫获取不同的视频 Packet
for (int i = 0; i < sum_count ; ++i) {
cv::Mat tempImage;
// 每次读取雷同工夫距离的图像并存入 vImage 中
while (av_read_frame(pFormatContext, pPacket) >= 0) {if (pPacket->stream_index == video_stream_index) {response = decode_packet_2mat(pPacket, pCodecContext, pFrame, tempImage);// 返回
}
if (response == 0)// 胜利读取一帧
break;
if (response < 0)
continue;
}
vImage.push_back(tempImage);
// 跳转视频
av_seek_frame(pFormatContext, -1, ((double)time_step / (double)1000)* AV_TIME_BASE*(double)(i+1) + (double)pFormatContext->start_time, AVSEEK_FLAG_BACKWARD);
}
3. 获取 Frame
在固定的工夫点可能无奈获取从以后工夫点的 Packet 获取对应的 Frame,所以须要对获取的 Packet 进行判断,如果没有获取到对应的 Frame 应该持续获取下一 Packet 直到获取到对应的 Frame 为止。
static int decode_packet_2mat(AVPacket* pPacket, AVCodecContext* pCodecContext, AVFrame* pFrame, cv::Mat& image) {int response = avcodec_send_packet(pCodecContext, pPacket);
if (response < 0) {logging("Error while sending a packet to the decoder");
return response;
}
while (response >= 0) {
// return decoded out data from a decoder
response = avcodec_receive_frame(pCodecContext, pFrame);
if (response == AVERROR(EAGAIN) || response == AVERROR_EOF) {logging("averror averror_eof");
break;
}
else if (response < 0) {logging("Error while receiving frame");
return response;
}
if (response >= 0) {
// 获取到 Frame
image = frame2Mat(pFrame, pCodecContext->pix_fmt);
}
return 0;
}
}
帧格局转换
因为从视频流获取的帧是 YUV 格局的 Frame 格局,前面应用 opencv 进行操作所以进行格局转换。
先应用 ffmpeg 中的 SwsContext 将从视频中抽取到的帧从 YUV 转换到 BGR 格局,再从 BGRFrame 中的内存中获取原始数据,并转换到 opencv 的 Mat 类型。
cv::Mat frame2Mat(AVFrame* pFrame, AVPixelFormat pPixFormat)
{
// image init
AVFrame* pRGBFrame = av_frame_alloc();
uint8_t* out_buffer = new uint8_t[avpicture_get_size(AV_PIX_FMT_BGR24, pFrame->width, pFrame->height)];
avpicture_fill((AVPicture*)pRGBFrame, out_buffer, AV_PIX_FMT_BGR24, pFrame->width, pFrame->height);
SwsContext* rgbSwsContext = sws_getContext(pFrame->width, pFrame->height, pPixFormat, pFrame->width, pFrame->height, AV_PIX_FMT_BGR24,SWS_BICUBIC, NULL, NULL, NULL);
if (!rgbSwsContext) {logging("Error could not create frame to rgbframe sws context");
exit(-1);
}
if (sws_scale(rgbSwsContext, pFrame->data, pFrame->linesize, 0, pFrame->height, pRGBFrame->data, pRGBFrame->linesize) < 0) {logging("Error could not sws to rgb frame");
exit(-1);
}
cv::Mat mRGB(cv::Size(pFrame->width, pFrame->height), CV_8UC3);
mRGB.data = (uchar*)pRGBFrame->data[0];// 留神不能写为:(uchar*)pFrameBGR->data
av_free(pRGBFrame);
sws_freeContext(rgbSwsContext);
return mRGB;
}
应用 opencv 建设画布并生成缩略图
通过画布须要的大小参数,画出红色画布,再对画布进行填充。
cv::Mat makeThumbnail(vector<cv::Mat> vImage, const unsigned int rowNums, const unsigned int colNums)
{
// 判断图片时候满足条件
if (vImage.size() != rowNums * colNums) {logging("Error image size not equal input size");
logging("vImage length: %d, rowNums: %d, col number: %d", vImage.size(), rowNums, colNums);
exit(-1);
}
int interval = 100;
int height = vImage[0].size().height * rowNums + interval * (rowNums + 1);
int width = vImage[0].size().width * colNums + interval * (colNums + 1);
logging("thumbnail size: %d * %d", height, width);
cv::Mat thumbnail(cv::Size(width, height), CV_8UC3);
thumbnail.setTo(255);
// 进行填充
for (int i = 0; i < rowNums; ++i) {for (int j = 0; j < colNums; ++j) {
int no = i * rowNums + j;
int widthOffset = (vImage[0].size().width + interval) * j + interval;
int heightOffset = (vImage[0].size().height + interval) * i + interval;
vImage[no].copyTo(thumbnail(cv::Rect(widthOffset, heightOffset, vImage[0].size().width, vImage[0].size().height)));
}
}
return thumbnail;
}
最初的成果