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• Synchronize RTSP with computer time

  4 novembre 2014, par Dídac Pérez

  I am successfully using libav to receive the video stream from an RTSP network source. The point is that I need to syncronize my computer’s time with the video capturing, meaning that I need to know which datetime of my computer corresponds to the first frame (pts = 0). My API calls are the following ones :

  av_register_all()
  
  avcodec_register_all()
  
  avformat_network_init()
  
  avformat_open_input()
  
  avformat_find_stream_info()
  
  av_read_play()
  
  loop
  
    av_init_packet()
  
    av_read_frame()
  
    [...]
  
    av_free_packet
  
  end loop

  With the calls above, I successfully read frames, but I do need to know how can I know the exact absolute datetime that corresponds to the first frame, since it has a pts of 0. Maybe I can use a time() function or GetSystemTime (I am using Windows) between two calls of the above, but do not really know how libav works.

• What do the special characters in an ffmpeg file output format mean ?

  3 février 2016, par Dan

  I need to process some videos with ffmpeg, and I found an example command that does almost everything I need it to :

  ffmpeg -i example.avi -vf fps=1/30 example_%03d.jpg

  I’ve figured out what all of this command does, but I’ve been unable to figure out the meaning of %03d in the output file format. What does %03d mean in a ffmpeg file output format mean ? What other special sequences are allowed in an ffmpeg output ?

• Issue regarding concatenate videos ffmpeg

  8 février 2021, par Mayank Thapliyal

  I want to concatenate 3 videos using ffmpeg. So I did a research on the net and got the required code. But later on I realized that it will not work as the attributes of the video are different and hence I will have to re-encode the videos

  


  So I got this on the internet :-

  


  ffmpeg -i 1.mp4-i 2.mp4 -i 3.mp4 -filter_complex "[0:v] [0:a] [1:v] [1:a] [2:v] [2:a] concat=n=3:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" output.mp4

  


  But when I ran it,it was SUPER slow. And ffmpeg recommended to add vsync 2 in the code. I added it in the following manner :-

  


  ffmpeg -i 1.mp4-i 2.mp4 -i 3.mp4 -vsync 2 -filter_complex "[0:v] [0:a] [1:v] [1:a] [2:v] [2:a] concat=n=3:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" output.mp4

  


  Now the video was processed on time and the result was also fine. But I don't know the meaning of the code. Will someone be kind enough to explain what exactly is happening ? (in this way I would be sure that the code will always work for me for all videos)