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• Extract frames from video at multiple time offsets (ffmpeg)

  17 mai 2021, par tech0123

  I am trying to extract frames from video using ffmpeg. My requirement is to extract frames at multiple time offsets. For 60 seconds video, frames may be requested at random time offsets - 5000ms, 7500ms, 15000ms, 17000ms. I understand there is an ss argument.

  


  ffmpeg -ss 00:00:05 -i <input /> -vframes 1 -q:v 2 output.jpg

  


  

  1. Rather running parallel ffmpeg processes, is there any way I can use -ss for multiple timestamps in just one ffmpeg command ?

  


  2. If time offsets are uniformly distributed (5s, 10s, 15s..), I can use either -r or fps to generate every N seconds. What is the difference between these 2 parameters ? Anything related to time it takes to get frames ?
Eg. frame every 4 seconds
ffmpeg -i <input />  -r 0.25 out_%04d.jpg
     
ffmpeg -i <input />  -vf fps=1/4 out_%04d.jpg

  


  


• Speed up FFmpeg processing time

  14 février 2020, par ahmed galal

  I’m using FFmpeg on android to :

  1- merge 3 videos

  2- add audio

  3- add logo

  4- trim one of the 3 videos

  5- change fps for the output

  I have implemented the right code but it took 30 min. for (120 fps, 1:17 min) video.
  I added the flag ( -preset ultrafast ) and time decreased to 6 min.
  I need the time to be shorter than 6min. (2-3 min). Is this possible ? Is there any better alternatives to ffmpeg ?

  This is my code for ffmpeg :

  String command2 = "-y -i " + logo + " -i " + intro + " -ss " + start + " -t " + (end-start) +
  
              " -async 1 -i " + inputFile + " -i " + outro + " -i " + audio
  
              + " -filter_complex [0]scale=1280*0.15:-1,colorchannelmixer=aa=0.5[o];" +
  
              "[1]fifo[v1];[2]fifo[v2];[3]fifo[v3];" +
  
              "[v1][v2][v3]concat=3[v];" +
  
              "[v][o]overlay=5:5[o3]" +
  
              " -map [o3] -map 4:a" +
  
              " -r " + fps + " -shortest -preset ultrafast -threads 8 -cpu-used 3 -c:a copy " + outFile;

• 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.