Trying to create a peak file from an audio file

General JUCE discussion
1

hello!

I’m trying to build a “peak array” to display an audio file waveform.

I wrote that piece of code :


        peaksArraySize = (int)(audioFormatReader->lengthInSamples/blockSize);
	peaksArray = BlockMinMax[peaksArraySize];

	int64 posInAudioFile = 0;
	int posInArray = 0;
	float minLeft = 1;
	float maxLeft = -1;
	float minRight = 1;
	float maxRight = -1;
	int buildingWaveformPercentCompleted;

	while (posInAudioFile < audioFormatReader->lengthInSamples) {
		buildingWaveformPercentCompleted = posInAudioFile*100/audioFormatReader->lengthInSamples;

		audioFormatReader->readMaxLevels(posInAudioFile,posInAudioFile+blockSize,minLeft,maxLeft,minRight,maxRight);
		peaksArray[posInArray].min = std::min(minLeft,minRight);
		peaksArray[posInArray].max = std::max(maxLeft,maxRight);

		posInAudioFile+=blockSize;
		posInArray++;

		peakBuildingInProgress(buildingWaveformPercentCompleted);
	}

	peaksAreBuilt();

but it’s very very slow, it seems to take exponentially more time as the file is read.

Should I use something else than the AudioFormatReader ?

Many thanks for helping a newbie!

Geoffroy

2

You should make sure you use a BufferedInputStream to buffer your FileInputStream - that’ll make a big difference.

3

Mmmm.

I used the following code to create my reader :

		//load file 
		File audioFile(fileName);

		AudioFormatManager audioFormatManager;
		audioFormatManager.registerBasicFormats();

		audioFormatReader = audioFormatManager.createReaderFor(audioFile);

		peaksArraySize = (int)(audioFormatReader->lengthInSamples/blockSize)+1;
		peaksArray = new BlockMinMax[peaksArraySize];

		buildPeakFile();

I tried to replace the createReaderFor call with a BufferedInputStream

		BufferedInputStream * bufferedInputStream = new BufferedInputStream(new FileInputStream(audioFile),blockSize*10,true);
		audioFormatReader = audioFormatManager.createReaderFor(bufferedInputStream);

(blockSize is 512 here)

but it’s even worse.

4

Check your parameters to readMaxLevel - looks to me like you’re reading the whole file instead of just the bit you want.

5

Thanks Jules!

You were right, the 2nd argument must be blockSize, not posInAudioFile+blockSize.

I will try not to ask for help when not needed anymore!