Avaudioconverter with Avaudioconverterinputblock Stutters Audio After Processing

AVAudioConverter with AVAudioConverterInputBlock stutters audio after processing

For anybody finding this, the actual underlying cause is the incorrect use of AVAudioConverterInputBlock. The destination buffer capacity doesn't matter as long as it is large enough, however the block will be called repeatedly until the destination buffer is filled.

If your source buffer contains ABC, it will fill up the destination with ABCABCABC.... Then, if you pipe it to realtime playback, the chunks are getting cut off randomly to fit the playback timing, resulting in this weird crackle.

The actual solution is to properly set AVAudioConverterInputStatus to .noDataNow once the buffer is submitted to the converter. Note that returning .endOfStream will lock up the converter object forever.

var gotData = false
self.converter.convert(to: convertedBuffer, error: nil, withInputFrom: { (_, outStatus) -> AVAudioBuffer? in
    if gotData {
        outStatus.pointee = .noDataNow
        return nil
    }
    gotData = true
    outStatus.pointee = .haveData
    return inputBuffer
})            

AVAudioConverter is broken in iOS 10

So, it turned out that the outBuffer frameLength has to be set to the frameCapacity. As default the length is 0 and is apparently treated differently on iOS 10

Related Topics