How can I write to an AVAssetWriter my custom float / shorts array?

Question

So i used AVAssetReader got the CMSampleBufferRefand then i got the samples values from CMBlockBufferRef data.

I then changed this samples with a custom filter.

Now i have an array of Shorts which i want to write back to a file, using AVAssetWriter.

My question here is how do I create back a CMSampleBufferRef and a CMBlockBufferRef to send to the AVAssetWriter?

Answer 1

Have a look at this apple developer page.

EDIT: Based on your comments, to create a samplebuffer directly from a shorts array, you should use Core Media Framework components, i.e. CMSampleBufferCreate

1. Convert sample data in shorts array to AudioBufferList
2. Convert the AudioBufferList to a CMSampleBuffer.

For example:

OSStatus status = noErr;
CMItemCount framesToProcess = 8192;
unsigned long sizeInBytes = framesToProcess * sizeof(SInt16);

// Init ABL from sample array
AudioBufferList *myAudioBufferList; // contains converted
myAudioBufferList = static_cast<AudioBufferList *>(calloc(1, offsetof(AudioBufferList, mBuffers) + (sizeof(AudioBuffer))));
myAudioBufferList->mNumberBuffers = 1;
myAudioBufferList->mBuffers[0].mNumberChannels = 1;
myAudioBufferList->mBuffers[0].mData = JoãoSamplesArrayPointer;
myAudioBufferList->mBuffers[0].mDataByteSize = (UInt32)sizeInBytes;

// sampleBuffer in (from the assetreader) you already have this
CMSampleBufferRef sampleBufferIn = [self.assetReaderAudioOutput copyNextSampleBuffer];

CMAudioFormatDescriptionRef format = CMSampleBufferGetFormatDescription(sampleBufferIn);
const AudioStreamBasicDescription *assetReaderOutputASBD = CMAudioFormatDescriptionGetStreamBasicDescription(format);

// setup output samplebuffer
CMSampleBufferRef sampleBufferOut = NULL;
CMSampleTimingInfo timing = { CMTimeMake(1, sampleRate), kCMTimeZero, kCMTimeInvalid };

// create description
status = CMAudioFormatDescriptionCreate(kCFAllocatorDefault, assetReaderOutputASBD, 0, NULL, 0, NULL, NULL, &format);

// create buffer
CMSampleBufferCreate( kCFAllocatorDefault, NULL, false, NULL, NULL, format, framesToProcess, 1, &timing, 0, NULL, &sampleBufferOut);

// put data into buffer from ABL (audio buffer list)
status = CMSampleBufferSetDataBufferFromAudioBufferList( sampleBufferOut, kCFAllocatorDefault,  kCFAllocatorDefault, 0, myAudioBufferList );

// write to assetwriter audioinput
BOOL success = [self.assetWriterAudioInput appendSampleBuffer:sampleBufferOut];
CFRelease(sampleBufferOut);