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• How to control key-frame generation of ffmpeg ?

  2 janvier 2013, par jAckOdE

  I'm making a segmenter that intervene ffmpeg's write_frame function and write output data to separate files. Each segmented file contains segment of about 3 seconds video.

  The code does following :

  1 - Get transcoded packet  
  
  2 - Check if it contains key frame data, if yes goto 3. 
  
  3 - Check the duration of current segment, if it exceed 3 seconds, goto 4 
  
  4 - Close file, and create new segment, write packet to segment file, goto-1

  General speaking, every segment contains at least 3 seconds video data, and it starts with a key frame.

  The problem is that the output video's duration are very different, some contain 3 seconds, some contain 5 or 6.

  I suspect that the problem due to how ffmpeg generate key frames during transcoding. If the "distance" between two adjacent keyframes are 6s, i got 6 seconds segment.

  Here is my questions :

  1. is that true that ffmpeg generate keyframes at irregular intervals (and interval time can be up to few second (eg. 6) ?

  2. How can we control the ffmpeg key frame generation ? (i guess there should be a ffmpeg command's argument for this, -force_key_frames maybe, but I'm not sure)

• JavaCV : How to use FrameGrabber for loading video, which is being written ?

  8 octobre 2014, par Sunshinetpu

  I try to merge 2 files :

  • Video file : this is result of screen recording (using command "/system/bin/screenrecord —size —bit-rate —time outputFile").
  • Audio file : this is result of audio recording (using MediaRecorder).

  When writing these files finishes, I try to merge them.
  But it takes a long time to merge these files. So I want to start merging files while they are being written. That means I use 3 threads :

  -1st thread : screen record - create file input.mp4.

  -2nd thread : audio record - create file input.mp3.

  -3rd thread : merge these file

  Here is my code to create FrameGrabbers from files input.mp4 and input.mp3, which are being written by another threads.

  String videoFile = Environment.getExternalStorageDirectory().getAbsolutePath()+"/input.mp4";
  
              String audioFile = Environment.getExternalStorageDirectory().getAbsolutePath()+"/input.mp3"; 
  
              FrameGrabber videoFrames = FFmpegFrameGrabber.createDefault(videoFile);
  
              FrameGrabber audioFrames = FFmpegFrameGrabber.createDefault(audioFile);
  
           videoFrames.start();

  Line "videoFrames.start()" gives error. Can any body help me to fix it ?

• avcodec/put_bits : Add functions for amount of bytes written/left

  25 mars 2021, par Andreas Rheinhardt

  avcodec/put_bits : Add functions for amount of bytes written/left
  Often a caller doesn't want the amount of bits written via a
  
  PutBitContext, but the amount of bytes. This in particular happens
  
  after one has flushed the PutBitContext (e.g. at the end of encoding,
  
  when one wants to know the actual packet size). The current way of doing
  
  this is with put_bits_count(pb)/8 (or (put_bits_count(pb) + 7)/8).
  Yet this has some issues : It contains implicit multiplications and
  
  divisions by 8 with a cast in between ; it obscurs the intent ; and
  
  it restricts the size of the buffer to (currently) INT_MAX/8 (or
  
  to 1/8 of the maximum of whatever put_bits_count() returns), although
  
  said restriction is not really necessary for users that don't need
  
  a bitcount.
  Corresponding functions for the amount of bytes left have also been
  
  addded.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/put_bits.h