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avfoundationmp3avaudiopcmbuffer

Failure to initialize a AVAudioCompressedBuffer

I'm trying to initialize an AVAudioCompressedBuffer using this format:

<AVAudioFormat 0x2818944b0:  2 ch,  48000 Hz, '.mp3' (0x00000000) 0 bits/channel, 0 bytes/packet, 1152 frames/packet, 0 bytes/frame>

like such:

AVAudioCompressedBuffer* compressedBuffer = [[AVAudioCompressedBuffer alloc] initWithFormat:format 
                                                                             packetCapacity:NUM_AQ_BUFS];

But I'm getting this exception:

Thread 1: "required condition is false: maximumPacketSize != 0"

What am I missing?

Thanks

Solution

  • You're using the wrong initializer. The header file for [AVAudioCompressedBuffer initWithFormat:packetCapacity:] says

    This fails if the format is PCM or if the format has variable bytes per packet (format.streamDescription->mBytesPerPacket == 0).

    and as you can see from the format, you have 0 bytes/packet.

    Use -[AVAudioCompressedBuffer packetCapacity:maximumPacketSize:] instead

    AVAudioCompressedBuffer* compressedBuffer = [[AVAudioCompressedBuffer alloc] initWithFormat:format packetCapacity:NUM_AQ_BUFS maximumPacketSize: 1024];

    tbh I don't know what the maximum packet size for mp3 should be. Apparently it's 144 bytes. You can query this with AudioCodecGetPropertyInfo() + kAudioCodecPropertyMaximumPacketByteSize or derive it from your own packet stream.