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• recording certain time range with ffmpeg

  22 août 2012, par Display Name

  I am having a RTSP enabled device.

  Could I use ffmpeg to capture recorded video from this device, including specifying the time range (date/time, such as clock=20120822T012345.440Z-20120822T045678.440Z) ? With RTSP, you would add a Range property for the PLAY command.

  The device does send H.264.

• How to insert bullet screen comments into a video by using ffmpeg ?

  7 septembre 2019, par Saeron Meng

  I would like to add some real-time comments in my video but I do not know how to use ffmpeg to realize this. The comments are like screen bullets through the screen, scrolling from right to left.

  My thought is to count the length of the comments and define speeds for them to move. Don’t worry about the source of the comments, I have already gotten them saved as an xml file. Also, I can transfer it into srt. For instance :

  <chat timestamp="671.195">
  
      <ems utctime="1562584080" sender="Bill">
  
          <richtext></richtext>
  
      </ems>
  
  </chat>
  
  <chat timestamp="677.798">
  
      <ems utctime="1562584086" sender="Jack">
  
          <richtext></richtext>
  
      </ems>
  
  </chat>

  The final result is like this (I did not find an example displayed in English), these fancy characters can move horizontally :

  

  I have searched some solutions on the Internet, most of which talk about how to write ass/srt files and add motionless subtitles. Like this :

  3
  
  00:00:39,770 --> 00:00:41,880
  
  When I was lying there in the VA hospital ...
  
  
  
  4
  
  00:00:42,550 --> 00:00:44,690
  
  ... with a big hole blown through the middle of my life,
  
  
  
  5
  
  00:00:45,590 --> 00:00:48,120
  
  ... I started having these dreams of flying.

  ffmpeg -i infile.mp4 -i infile.srt -c copy -c:s mov_text outfile.mp4

  But I need another kind of "subtitles" which can move.

  So my question is, how to modify the ffmpeg command and the template of srt file so as to arrange the subtitles from the top to the bottom and let them move from right to left ?

• Frequency response of ffmpeg filters

  13 novembre 2020, par Dr_Click

  I'm using ffmpeg to decode and encode signal. It works perfectly and I added filters. For example, I'm using such a command :

  


  ffmpeg -re -i /home/dr_click/live.wav -af "anequalizer=c0 f=200 w=100 g=-5 t=0|c1 f=200 w=100 g=-5 t=0, anequalizer=c0 f=1000 w=100 g=3 t=0|c1 f=1000 w=100 g=3 t=0" -acodec pcm_s16be -ar 44100 -ac 2 -f rtp rtp://127.0.0.1:1234


  


  I'm streaming my file, adding 2 filters with 200 Hz and 1000 Hz as central frequency and 100 Hz width and it works.

  


  With such a filter, I know my gain will be -5db at 200Hz. But what is the gain for frequencies at 250 Hz ? Still -5db ? -4.5db ? -3db ? And same question at 350Hz or any other frequency.

  


  What I'm looking for and didn't found is the way to get the frequency response of such a filter for a bandwith from 20Hz to 20kHz. In other words, what I'd like to know for any frequency is : gain = f (frequency) with a given ffmpeg filter

  


  Thank you for your help,

  


  Dr_Click