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• Can ffmpeg record more than two audio tracks ? (Linux)

  27 novembre 2017, par Toby Eggitt

  I want to record four microphones, independently but concurrently and on the same clock (so they stay synchronized over long recording periods). I’m accustomed to grabbing two microphones (as left and right channels) using ffmpeg on Linux, and would like to use the same basic approach for the four.

  I believe I’ve found several USB-based devices that will allow sending four multiplexed audio signals, digitized, through a single USB port, but it’s not clear to me how I would capture this data into a single file. I’ve never worked with an audio file containing more than a left and right stereo track. (well, that and a video track, I suppose :)

  Part of the problem is that I can’t "just try it", since I don’t want to buy the non-trivially-priced device if it’s not going to be usable.

  Does anyone know if this is possible ? If so, does it "just work" when ffmpeg sees such a data stream, or is there some config I need to do (and if so, any hints on what, or where to find the information, would be most welcome).

  TIA !

• how to call a tcl file from another tcl file

  28 novembre 2017, par M. D. P

  i need to call a tcl file which hold the code for capturing image from another tcl file.

  for example i my image.tcl file code is as follow :

  proc image {}  { 
  
  
  
  set time [clock format [clock seconds] -format %Y%m%d_%H%M%S]
  
     
  
  exec ffmpeg -f dshow -s 1280x720 -i "video=Integrated Webcam" -benchmark c:/test/sample_$time.jpg
  
          
  
  }
  
  image

  so, i want to call this image.tcl file from another tcl file called main.tcl,so the code for main.tcl can be as follow :

  proc a {}  { 
  
  
  
  "c:/test/image.tcl"
  
  
  
  "c:/test/video.tcl" 
  
  
  
  "c:/test/live.tcl"
  
          
  
  }
  
  a

  the above tcl script should run one after another when i call main.tcl

  any solution for this. add the code as answer. thanks.

• FFMPEG : embed current time in milliseconds into video

  22 décembre 2023, par stevendesu

  I would like to embed the computer's local time in milliseconds into a stream using FFMPEG.

  



  I can embed the local time in seconds using drawtext like so :

  



  ffmpeg -i <input /> -vf "drawtext=text=&#x27;%{localtime\:%T}&#x27;" -f flv <output>&#xA;</output>

  



  Looking through the documentation for drawtext, doing some tests, and Googling around, it seems like localtime and gmtime don't provide milliseconds — just seconds. However the pts options does have milliseconds :

  



  ffmpeg -i <input /> -vf "drawtext=text=&#x27;%{pts\:hms}&#x27;" -f flv <output>&#xA;</output>

  



  I also found out that pts supports an offset, so I was able to use something like this to display local time (kind of) :

  



  ffmpeg -i <input /> -vf "drawtext=text=&#x27;%{pts\:hms\:$(date &#x2B;%s.%N)}&#x27;" -f flv <output>&#xA;</output>

  



  This had two problems :

  



  

  1. It displayed something like 17499:17:29 for the time... I found a (rather complex) way to work around this

  


  2. It uses the server's current time when you first run the ffmpeg command as the offset — not the server's current time when ffmpeg actually starts decoding video. I noticed ffmpeg had about a 2-second startup time, causing the clock to be off by roughly 2 seconds

  


  



  Is there a way to modify my solution, or an entirely separate solution, that can embed server local time in milliseconds into the stream ?