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• Getting accurate time from FFMPeg with Objective C (Audio Queue Services)

  2 avril 2012, par Winston

  My iPhone app plays an audio file using FFMPeg.

  I'm getting the elapsed time (to show to user) from the playing audio (in minutes and seconds after converting from microseconds, given by FFMPeg) like so :

  AudioTimeStamp currentTimeStamp;
  
  AudioQueueGetCurrentTime (audioQueue, NULL, &currentTimeStamp, NULL);
  
  
  
  getFFMPEGtime = currentTimeStamp.mSampleTime/self.basicAudioDescription.mSampleRate;
  
  
  
  self.currentAudioTime = [NSString stringWithFormat: @"%02d:%02d",
  
                              (int) getFFMPEGtime / (int)60000000,
  
                              (int) ((getFFMPEGtime % 60000000)/1000000)];

  Everything works fine, but when I scrub back or forward to play another portion of the song, the elapsed time will go back to zero, no matter the current position. The timer will always zero out.

  I know I'm suposed to do some math to keep track of the old time and the new time, maybe constructing another clock or so, perhaps implementing another callback function, etc... I'm not sure what way I should go.

  My questions are :

  1) What's the best approach to keep track of the elapsed time when going back/forward in a song, avoiding the clock to always going back to zero ?

  2) Should I look deeply into FFMPeg functions or should I stick with Objective-C and Cocoa Touch for solving this problem ?

  Please, I need some advices/ideas from experienced programmers. I'm stuck. Thanks beforehand !

• Displaying YUV420 data using Opengles shader is too slow

  28 novembre 2012, par user1278982

  I have a child thread called A to decode video using ffmpeg on iPhone 3GS, another thread called B to display yuv data, in thread B, I used glSubTexImage2D to upload Y U V textures, and then convert yuv data to RGB in shader, but the frame rate in the decode thread is only 15fps.Why ?

  Update :
  The frame size is 720 * 576.
  I also found something interesting that if I didn't start the thread displaying the YUV data, the frame rate calculated in the decode thread is 22 fps,otherwise 15 fps.So I think that my displaying method must be inefficient.the code as below.

  I have a callback in the decode thread :

  typedef struct _DVDVideoPicture
  
  {
  
     char *plane[4];
  
     int iLineSize[4];
  
  }DVDVideoPicture;
  
  
  
  void YUVCallBack(void *pYUVData, void *pContext)
  
  {
  
     VideoView *view = (VideoView *)pContext;
  
     [view.glView copyYUVData:(DVDVideoPicture *)pData];
  
     [view calculateFrameRate];
  
  }

  The copyYUVData method extract the y u v planes separately. The following is displaying thread method.

• What can be the substitute for SDL to direct ffmpeg decoded videos to screen in IOS ?

  18 octobre 2012, par jAckOdE

  I making a iOS video player using ffmpeg, the flow likes this :

  Video File---> [FFMPEG Decoder] —> decoded frames —> [a media director] —> /iphone screen (full and partial)/

  A media director will handle the tasks of rendering decoded video frames to iOS ui (UIView, UIWindow etc), outputting audio samples to iOS speaker, and threads management.

  SDL is one of those libs, but SDL is mainly made for game making purpose and seem to be not really mature for iOS.

  What can be the substitute for SDL ?