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• Accurate FFmpeg capture start time

  28 juillet 2016, par Adam

  I’m using ffmpeg from the command line to capture from a webcam to a file using the following :

  ffmpeg -y -rtbufsize 702000k -f dshow -s 320x240 -r 25 -i video="<device>" -t 10 -vcodec mjpeg -q:v 2 out.mp4
  
  </device>

  There is a slight delay between executing the command and the start of the capture ( 0.5 sec).
  I’m trying to find a way to accurately determine the start time (UTC/GMT) of the capture.

  My initial thought was to use the file-creation time as this might accurately reflect when the first frame was encoded (as opposed to when the command was executed). Unfortunately the file creation time is only accurate to the second which is not precise enough (and I’m not sure this would have given an accurate result anyway).

  My next thought was to use ffmpegs timestamp option. According to the documentation (http://www.ffmpeg.org/ffmpeg.html) :

  ‘-timestamp time (output)’

  Set the recording timestamp in the container. The syntax for time is:
  
  
  
  now|([(YYYY-MM-DD|YYYYMMDD)[T|t| ]]((HH:MM:SS[.m...])|(HHMMSS[.m...]))[Z|z])

  If the value is "now" it takes the current time. Time is local time unless ’Z’ or
  ’z’ is appended, in which case it is interpreted as UTC. If the year-month-day part
  is not specified it takes the current year-month-day.

  So I added the option :

  ffmpeg -y -rtbufsize 702000k -f dshow -s 320x240 -r 25 -i video="<device>" -t 10 -vcodec mjpeg -q:v 2 -timestamp now out.mp4
  
  </device>

  Unfortunately ffmpeg doesn’t seem to like this :

  Option timestamp (set the recording timestamp (’now’ to set the
  current time)) cannot be applied to output file out.mp4 — you are
  trying to apply an input option to an output file or vice versa. Move
  this option before the file it belongs to.

  Error parsing options for output file out.mp4.

  Error opening output files : Error number -22 occurred

  The documentation says -timestamp is an output option and it appears to be applied to the output file so I’m confused by this error.

  Can anyone suggest a way to accurately determine the capture start time ?

  Does anyone know why the -timestamp option gives an error ?

• 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;