RTSP ffmpeg set flags

serkan · August 29, 2023, 11:27am

There is a lot of latency when capture RTSP stream. When using ffplay with -fflags nobuffer -flags low_delay almost no latency. How can i pass this flags to ffmpeg via opencv. If it is not possible can i change source code of opencv to set flags?

cudawarped · August 29, 2023, 4:07pm

If you are not on Windows I would think setting this with av_dict_set should work, see

github.com

opencv/opencv/blob/8a1b998b2ba3993919deafd137a33f55fce2c962/modules/videoio/src/cap_ffmpeg_impl.hpp#L1122


      
              ic = avformat_alloc_context();
              ic->interrupt_callback.callback = _opencv_ffmpeg_interrupt_callback;
              ic->interrupt_callback.opaque = &interrupt_metadata;
          #endif
          
          #ifndef NO_GETENV
              char* options = getenv("OPENCV_FFMPEG_CAPTURE_OPTIONS");
              if(options == NULL)
              {
          #if LIBAVFORMAT_VERSION_MICRO >= 100  && LIBAVFORMAT_BUILD >= CALC_FFMPEG_VERSION(55, 48, 100)
                  av_dict_set(&dict, "rtsp_flags", "prefer_tcp", 0);
          #else
                  av_dict_set(&dict, "rtsp_transport", "tcp", 0);
          #endif
              }
              else
              {
                  CV_LOG_DEBUG(NULL, "VIDEOIO/FFMPEG: using capture options from environment: " << options);
          #if LIBAVUTIL_BUILD >= (LIBAVUTIL_VERSION_MICRO >= 100 ? CALC_FFMPEG_VERSION(52, 17, 100) : CALC_FFMPEG_VERSION(52, 7, 0))
                  av_dict_parse_string(&dict, options, ";", "|", 0);
          #else

It is however possible the delay is due to the fact you are not requesting the frames quickly enough in which case this might not make any difference.

serkan · August 31, 2023, 11:48am

Thank you. I use Windows. A seperate thread captures the stream. After your answer, I set environment variable OPENCV_FFMPEG_CAPTURE_OPTIONS =fflags;nobuffer|flags;low_delay but i did not work. Then i changed source code cap_ffmpeg_impl.hpp. I compiled in Visual Studio but nothing changed. I think it compiled from binary opencv_videoio_ffmpeg_64.dll. i changed cmakelist.txt of videoio add src cap_ffmpeg.cpp caused a lot of lib error.

cudawarped · August 31, 2023, 11:50am

That’s correct which is why my comment above specified not on windows.

In windows you can try building against FFMpeg, see

serkan · September 1, 2023, 12:27pm

I decided tobuild opencv with gstreamer. Then i used latency=0 parameter in rtsp uri this solved my problem. thank you for your help.

Topic		Replies	Views
Videocapture open lag with rtsp C++ rtsp , videoio	12	2125	November 7, 2022
Cannot read RTSP Stream with less than 1 FPS Python videoio	14	3499	July 12, 2022
VideoCapture() does not work with udp protocol Python rtsp , programming , imutils	21	3687	January 18, 2023
Delay problem when capturing RTSP video C++ gstreamer , videoio	0	1356	January 1, 2022
Capture from local device vs tcpstream Python videoio	0	1109	June 29, 2022

RTSP ffmpeg set flags

Related Topics