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SkeyePlayer RTSP Windows 端 (下文简称：SkeyePlayer) 播放器之前抓图代码次要通过 OpenCV 来实现，且数据格式转换的效率过于低下；故而在过后的代码中采纳线程机制来解决抓图导致视频播放时卡顿的问题；而最新版的 SkeyePlayer 为了精简代码也为了进步抓图效率，咱们采纳 ffmpeg 进行抓图，为了保障视频播放的流畅性，线程机制咱们依然保留。
采纳 ffmpeg 进行抓图代码如下
// 抓图函数实现
int take_snapshot(char *file, int w, int h, uint8_t *buffer, AVPixelFormat Format)
{
char *fileext = NULL;
enum AVCodecID codecid = AV_CODEC_ID_NONE;
struct SwsContext *sws_ctx = NULL;
AVPixelFormat swsofmt = AV_PIX_FMT_NONE;
AVFrame picture = {};
int ret = -1;
AVFormatContext *fmt_ctxt = NULL;
AVOutputFormat *out_fmt = NULL;
AVStream *stream = NULL;
AVCodecContext *codec_ctxt = NULL;
AVCodec *codec = NULL;
AVPacket packet = {};
int retry = 8;
int got = 0;
// init ffmpeg
av_register_all();
fileext = file + strlen(file) - 3;
if (_stricmp(fileext, "png") == 0) {
codecid = AV_CODEC_ID_APNG;
swsofmt = AV_PIX_FMT_RGB24;
}
else {
codecid = AV_CODEC_ID_MJPEG;
swsofmt = AV_PIX_FMT_YUVJ420P;
}
AVFrame video;
int numBytesIn;
numBytesIn = av_image_get_buffer_size(Format, w, h, 1);
av_image_fill_arrays(video.data, video.linesize, buffer, Format, w, h, 1);
video.width = w;
video.height = h;
video.format = Format;
// alloc picture
picture.format = swsofmt;
picture.width = w > 0 ? w : video.width;
picture.height = h > 0 ? h : video.height;
int numBytes = av_image_get_buffer_size(swsofmt, picture.width, picture.height , 1);
buffer = (uint8_t *)av_malloc(numBytes * sizeof(uint8_t));
av_image_fill_arrays(picture.data, picture.linesize, buffer, swsofmt, picture.width, picture.height, 1);
// scale picture
sws_ctx = sws_getContext(video.width, video.height, (AVPixelFormat)Format/*video->format*/,
picture.width, picture.height, swsofmt, SWS_FAST_BILINEAR, NULL, NULL, NULL);
if (!sws_ctx) {//av_log(NULL, AV_LOG_ERROR, "could not initialize the conversion context jpg\n");
goto done;
}
sws_scale(sws_ctx, video.data, video.linesize, 0, video.height, picture.data, picture.linesize);
// do encoding
fmt_ctxt = avformat_alloc_context();
out_fmt = av_guess_format(codecid == AV_CODEC_ID_APNG ? "apng" : "mjpeg", NULL, NULL);
fmt_ctxt->oformat = out_fmt;
if (!out_fmt) {//av_log(NULL, AV_LOG_ERROR, "failed to guess format !\n");
goto done;
}
if (avio_open(&fmt_ctxt->pb, file, AVIO_FLAG_READ_WRITE) < 0) {//av_log(NULL, AV_LOG_ERROR, "failed to open output file: %s !\n", file);
goto done;
}
stream = avformat_new_stream(fmt_ctxt, 0);
if (!stream) {//av_log(NULL, AV_LOG_ERROR, "failed to create a new stream !\n");
goto done;
}
codec_ctxt = stream->codec;
codec_ctxt->codec_id = out_fmt->video_codec;
codec_ctxt->codec_type = AVMEDIA_TYPE_VIDEO;
codec_ctxt->pix_fmt = swsofmt;
codec_ctxt->width = picture.width;
codec_ctxt->height = picture.height;
codec_ctxt->time_base.num = 1;
codec_ctxt->time_base.den = 25;
codec = avcodec_find_encoder(codec_ctxt->codec_id);
if (!codec) {//av_log(NULL, AV_LOG_ERROR, "failed to find encoder !\n");
goto done;
}
if (avcodec_open2(codec_ctxt, codec, NULL) < 0) {//av_log(NULL, AV_LOG_ERROR, "failed to open encoder !\n");
goto done;
}
while (retry-- && !got) {if (avcodec_encode_video2(codec_ctxt, &packet, &picture, &got) < 0) {//av_log(NULL, AV_LOG_ERROR, "failed to do picture encoding !\n");
goto done;
}
if (got) {ret = avformat_write_header(fmt_ctxt, NULL);
if (ret < 0) {//av_log(NULL, AV_LOG_ERROR, "error occurred when opening output file !\n");
goto done;
}
av_write_frame(fmt_ctxt, &packet);
av_write_trailer(fmt_ctxt);
}
}
// ok
ret = 0;
done:
avcodec_close(codec_ctxt);
if (fmt_ctxt)
{avio_close(fmt_ctxt->pb);
}
avformat_free_context(fmt_ctxt);
av_packet_unref(&packet);
sws_freeContext(sws_ctx);
av_free(buffer);
return ret;
}借助 ffmpeg 弱小的视频解决和转换性能，咱们能够将一帧图像转换成任意格局的图片，当然如代码所示咱们只选择性地反对了“jpeg”和“png”两种格局的图片格式；
采纳 ffmpeg 抓图的步骤分两步：
- 须要将图像转换成指定的格局，当然弱小的格局转换函数也反对图像的缩放，且效率很高；
- 图像编码，仔细的同学不难发现，ffmpeg 的编码和存文件 / 推送流的代码是通用的，这套代码能够用来抓图也能够用来编码 H264、265 等而后存文件（如 MP4 等）或者推送 RTMP/RTSP 等；
曾经实现了抓图代码调用起来就很简略了，只需替换掉旧的抓图函数即可，须要留神的是之前的抓图固定了格局为 YUY2，所以缓冲区大小只有 WidthHeight 2 的大小，而显然 RGB24 格局的数据会导致缓冲区溢出，所以，咱们须要从新定义缓冲区的大小，如下代码所示：
// 抓图
if (pThread->manuScreenshot == 0x01)//Just support jpeg，png
{unsigned int timestamp = (unsigned int)time(NULL);
time_t tt = timestamp;
struct tm *_time = localtime(&tt);
char szTime[64] = {0,};
strftime(szTime, 32, "%Y%m%d-%H%M%S", _time);
// char strPath[512] = {0,};
// sprintf(strPath , "%sch%d_%s.jpg", pThread->strScreenCapturePath, pThread->channelId, szTime) ;
PhotoShotThreadInfo* pShotThreadInfo = new PhotoShotThreadInfo;
sprintf(pShotThreadInfo->strPath , "%sch%d_%s.jpg", pThread->strScreenCapturePath, pThread->channelId, szTime) ;
int nYuvBufLen = frameinfo.width*frameinfo.height*3;// most size = RGB24, we donot support RGBA Render type
pShotThreadInfo->pYuvBuf = new unsigned char[nYuvBufLen];
pShotThreadInfo->width = frameinfo.width;
pShotThreadInfo->height = frameinfo.height;
pShotThreadInfo->renderFormat = pThread->renderFormat ;
memcpy(pShotThreadInfo->pYuvBuf, pThread->yuvFrame[pThread->decodeYuvIdx].pYuvBuf, pThread->yuvFrame[pThread->decodeYuvIdx].Yuvsize-1);
CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)_lpPhotoShotThread, pShotThreadInfo, 0, NULL);
pThread->manuScreenshot = 0;
}目前咱们所反对的最大数据格式是 RGB24，所以咱们定义了 WidthHeight3+ 1 的最大缓冲区大小，其实这里能够优化一下，就是依据具体的 renderFormat 来定义缓冲区的大小，从而防止不必要的内存资源节约，这会在后续版本进行优化。
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