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• Meaning of Timestamp Retrieved by AudioQueueGetCurrentTime() in AudioQueue Callback

  30 juillet 2024, par White0930

  I'm working on an audio project and have a question regarding the meaning of the timestamp retrieved by AudioQueueGetCurrentTime().

  


  According to the Apple Developer Documentation, the following calculation gives the audio time being played (since AudioQueueStart) :

  


  - (Float64) GetCurrentTime {
    AudioTimeStamp c;       
    AudioQueueGetCurrentTime(playState.queue, NULL, &c, NULL);  
    return c.mSampleTime / _av->audio.sample_rate;
}


  


  However, in a project I'm working on, I noticed the following code inside the fillAudioBuffer callback function of AudioQueue :

  


  
static void fillAudioBuffer(AudioQueueRef queue, AudioQueueBufferRef buffer){
    
    int lengthCopied = INT32_MAX;
    int dts= 0;
    int isDone = 0;

    buffer->mAudioDataByteSize = 0;
    buffer->mPacketDescriptionCount = 0;
    
    OSStatus err = 0;
    AudioTimeStamp bufferStartTime;

    AudioQueueGetCurrentTime(queue, NULL, &bufferStartTime, NULL);
    

    
    while(buffer->mPacketDescriptionCount < numPacketsToRead && lengthCopied > 0){
        if (buffer->mAudioDataByteSize) {
            break;
        }
        
        lengthCopied = getNextAudio(_av,buffer->mAudioDataBytesCapacity-buffer->mAudioDataByteSize, (uint8_t*)buffer->mAudioData+buffer->mAudioDataByteSize,&dts,&isDone);
        if(!lengthCopied || isDone) break;
      
        if(aqStartDts < 0) aqStartDts = dts;
        if (dts>0) currentDts = dts;
        if(buffer->mPacketDescriptionCount ==0){
            bufferStartTime.mFlags = kAudioTimeStampSampleTimeValid;
            bufferStartTime.mSampleTime = (Float64)(dts-aqStartDts) * _av->audio.frame_size;
            
            if (bufferStartTime.mSampleTime <0 ) bufferStartTime.mSampleTime = 0;
            PMSG2("AQHandler.m fillAudioBuffer: DTS for %x: %lf time base: %lf StartDTS: %d\n", (unsigned int)buffer, bufferStartTime.mSampleTime, _av->audio.time_base, aqStartDts);
            
        }
        buffer->mPacketDescriptions[buffer->mPacketDescriptionCount].mStartOffset = buffer->mAudioDataByteSize;
        buffer->mPacketDescriptions[buffer->mPacketDescriptionCount].mDataByteSize = lengthCopied;
        buffer->mPacketDescriptions[buffer->mPacketDescriptionCount].mVariableFramesInPacket = _av->audio.frame_size;
        
        buffer->mPacketDescriptionCount++;
        buffer->mAudioDataByteSize += lengthCopied;
        
    }
    
#ifdef DEBUG
    int audioBufferCount, audioBufferTotal,  videoBufferCount, videoBufferTotal;
    bufferCheck(_av,&videoBufferCount, &videoBufferTotal, &audioBufferCount, &audioBufferTotal);
    
    PMSG2("AQHandler.m fillAudioBuffer: Video Buffer: %d/%d Audio Buffer: %d/%d\n", videoBufferCount, videoBufferTotal, audioBufferCount, audioBufferTotal);
    
    PMSG2("AQHandler.m fillAudioBuffer: Bytes copied for buffer 0x%x: %d\n",(unsigned int)buffer, (int)buffer->mAudioDataByteSize );
#endif  
    if(buffer->mAudioDataByteSize){
        
        if(err=AudioQueueEnqueueBufferWithParameters(queue, buffer, 0, NULL, 0, 0, 0, NULL, &bufferStartTime, NULL))
        {
#ifdef DEBUG
            char sErr[10];

            PMSG2(@"AQHandler.m fillAudioBuffer: Could not enqueue buffer 0x%x: %d %s.", buffer, err, FormatError(sErr, err));
#endif
        }
    }

}


  


  Based on the documentation for AudioQueueEnqueueBufferWithParameters and the variable naming used by the author, bufferStartTime seems to represent the time when the newly filled audio buffer will start playing, i.e., the time when all current audio in the queue has finished playing and the new audio starts. This interpretation suggests bufferStartTime is not the same as the time of the audio currently being played.

  


  I have browsed through many related questions, but I still have some doubts.. I'm currently fixing an audio-video synchronization issue in my project, and there isn't much detailed information in the Apple Developer Documentation (or maybe my search skills are lacking).

  


  Can someone clarify the exact meaning of the timestamp returned by AudioQueueGetCurrentTime() in this context ? Is it the time when the current audio will finish playing, or is it the time when the new audio will start playing ? Any additional resources or documentation that explain this in detail would also be appreciated.

  


• What does the summary output of the coding with ffmpeg means

  12 novembre 2015, par Jai

  I am working with video comparison using ffmpeg. By Using ffmpeg command I can find the difference between 2 videos. But i want to find the percentage different in 2 videos.
  From the below ffmpeg output how can i found the percentage difference in two videos. Which attribute denote the difference.?

  TaskList: video:530kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.266679%
  
  TaskList: [libx264 @ 0000000002750b00] frame I:2     Avg QP:23.92  size: 29796
  
  TaskList: [libx264 @ 0000000002750b00] frame P:97    Avg QP:22.97  size:  4477
  
  TaskList: [libx264 @ 0000000002750b00] frame B:9     Avg QP:28.16  size:  5338
  
  TaskList: [libx264 @ 0000000002750b00] consecutive B-frames: 83.3% 16.7%  0.0%  0.0%
  
  TaskList: [libx264 @ 0000000002750b00] mb I  I16..4: 25.7% 37.8% 36.5%
  
  TaskList: [libx264 @ 0000000002750b00] mb P  I16..4:  1.9%  4.5%  1.0%  P16..4: 26.7%  8.8%  3.8%  0.0%  0.0%    skip:53.3%
  
  TaskList: [libx264 @ 0000000002750b00] mb B  I16..4:  0.7%  2.4%  2.7%  B16..8: 19.9%  8.8%  2.6%  direct: 4.7%  skip:58.2%  L0:32.3% L1:53.2% BI:14.4%
  
  TaskList: [libx264 @ 0000000002750b00] 8x8 transform intra:55.1% inter:69.5%
  
  TaskList: [libx264 @ 0000000002750b00] coded y,uvDC,uvAC intra: 55.6% 70.0% 24.2% inter: 19.8% 26.7% 2.5%
  
  TaskList: [libx264 @ 0000000002750b00] i16 v,h,dc,p: 25% 44%  5% 27%
  
  TaskList: [libx264 @ 0000000002750b00] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 24% 26% 17%  5%  5%  6%  5%  6%  6%
  
  TaskList: [libx264 @ 0000000002750b00] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 26% 29% 13%  5%  5%  6%  5%  6%  5%
  
  TaskList: [libx264 @ 0000000002750b00] i8c dc,h,v,p: 44% 30% 20%  5%
  
  TaskList: [libx264 @ 0000000002750b00] Weighted P-Frames: Y:6.2% UV:4.1%
  
  TaskList: [libx264 @ 0000000002750b00] ref P L0: 64.2% 28.5%  5.8%  1.3%  0.1%
  
  TaskList: [libx264 @ 0000000002750b00] ref B L0: 88.4% 11.6%
  
  TaskList: [libx264 @ 0000000002750b00] kb/s:1204.25

• nomenclature #3465 : Nouvelle balise : #LOGO

  6 juin 2015, par Fil Up

  qu’affiche-t-on si l’article n’a pas de logo ? un autre logo (la rubrique parente, ou à défaut le site) ? ou rien ?