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• JavaCV FFmpegFrameRecorder properties explanation needed

  29 décembre 2014, par Leron

  I’m using FFmpegFrameRecorder to get the video input from my webcam and record it into a video file. The problem is that I’m building my application using a few different demo source codes that I found and I use properties some of which are not completely clear to me.

  First, here is my code snippet :

  FFmpegFrameRecorder recorder = new FFmpegFrameRecorder(FILENAME,  grabber.getImageWidth(),grabber.getImageHeight());
  
  
  
          recorder.setVideoCodec(13);
  
          recorder.setFormat("mp4");
  
          recorder.setPixelFormat(avutil.PIX_FMT_YUV420P);
  
          recorder.setFrameRate(30);
  
          recorder.setVideoBitrate(10 * 1024 * 1024);
  
  
  
          recorder.start();

  • setVideoCodec(13) - What is the meaning of this (13) how can I understand what actual codec stands behind any number ?
  • setPixelFormat - Just get this, don’t know what it’s doing in general
  • setFrameRate(30) - I think this should be pretty clear but still what is the logic behind what frame rate we choose (isn’t the high the better ?)
  • setVideoBitrate(10*1024*1024) - again almost no idea what this does and what’s the logic behind the numbers ?

  At the end I just want to mention one last problem that I get recording video like this. If the actual length of the video is let’s say 20secs. When I play the video file created from the program it runs significantly faster. Can’t tell if it’s exactly 2 times faster than it should be but in general if I record a 20sec video then it’s played for about 10secs. What may cause this and how can I fix it ?

• Fix min/max validation. Closes gh-666. Fixes #648

  20 mars 2013, par ekonijn

  Fix min/max validation. Closes gh-666. Fixes #648
  In 1.10.0, min/max validation was supported for input type="text",
  
  where min/max were interpreted as numbers.  This means min/max
  
  for date would not work : min="2012-02-13" was interpreted as min="Not a Number".
  In 1.11.0, min/max were no longer converted to numbers.  This means
  
  min/max for dates worked, but min/max for numbers failed :
  
  "50" < "150" < "1000" does not hold.
  For an example, see http://jsbin.com/awokex/3
  This commit makes the behaviour of min/max dependent on input type :
   * input type=text (or not type attribute) has numeric min/max, as in 1.10.0
  
   * input type=date has working min/max for type date ;
  
     on mobile browsers you also get a date picker,
  
     plus the browser may reject invalid dates before
  
     javascript gets a chance to complain.
  
   * input type=number or range get numeric min/max,
  
     plus numeric keypad or slider on mobile browsers,
  
     plus browser may reject invalid input before javascript
  
     gets a chance to complain
  Allowing use of min/max with type=number/range/date is important
  
  for mobile browsers, where the numeric keypad or date picker
  
  make the input much easier to use than a generic text input field.
  
  In this situation jquery-validate remains necessary to support
  
  older browsers that do not do input validation based on type
  
  and min/max.
  For situations where numeric input should be validated by jquery
  
  without giving the browser a chance to validate the input format,
  
  input type=text in combination with min/max can be used, as in 1.10.0.
  

• Problem with ffmpeg function avformat_seek_file()

  19 avril 2013, par Kael

  I am trying to seek the given frame in the video using ffmpeg library. I knew that there is av_seek_frame() function but it was recommended to use avformat_seek_file()instead. Something similar mentioned here. I know that avformat_seek_file() can't always take you to exact frame you want, but this is ok for me. I just want to jump to the nearest keyframe. So i open the video, find videostream and calling it like this :
  avformat_seek_file( formatContext, streamId, 0, frameNumber, frameNumber, AVSEEK_FLAG_FRAME ). It always returns 0, so i understand it as correct finish. However, it doesn't work as it should to. I check byte position like here before and after calling avformat_seek_file(). Actually it changes, but it changes always in the same way whenever i'm trying to put different target frame numbers ! I mean that byteposition after this call is always same even with different frameNumber values. Obviously, i'm doing something wrong but i don't know what exactly. I don't know if it does matter but i'm using .h264 files for that. I tried different flags, different files, using timestamps instead of frames, flushing buffers before and after and so on but it doesn't work for me. I will be very grateful if someone could show me what is wrong with it.