创建静音音频CMSampleBufferRef

问题描述

如何在Swift中创建无声音频 CMSampleBufferRef ？我希望将无声 CMSampleBufferRef 附加到 AVAssetWriterInput 的实例。

How do you create a silent audio CMSampleBufferRef in Swift? I am looking to append silent CMSampleBufferRefs to an instance of AVAssetWriterInput.

推荐答案

你没有说你想要什么格式的零（整数/浮点，单声道/立体声，采样率），但也许没关系。无论如何，这是在swift中创建静音CD音频样式 CMSampleBuffer 的一种方法。

You don't say what format you want your zeros (integer/floating point, mono/stereo, sample rate), but maybe it doesn't matter. Anyway, here's one way to create a silent CD audio style CMSampleBuffer in swift.

func createSilentAudio(startFrm: Int64, nFrames: Int, sampleRate: Float64, numChannels: UInt32) -> CMSampleBuffer? {
    let bytesPerFrame = UInt32(2 * numChannels)
    let blockSize = nFrames*Int(bytesPerFrame)

    var block: CMBlockBuffer?
    var status = CMBlockBufferCreateWithMemoryBlock(
        kCFAllocatorDefault,
        nil,
        blockSize,  // blockLength
        nil,        // blockAllocator
        nil,        // customBlockSource
        0,          // offsetToData
        blockSize,  // dataLength
        0,          // flags
        &block
    )
    assert(status == kCMBlockBufferNoErr)

    // we seem to get zeros from the above, but I can't find it documented. so... memset:
    status = CMBlockBufferFillDataBytes(0, block!, 0, blockSize)
    assert(status == kCMBlockBufferNoErr)

    var asbd = AudioStreamBasicDescription(
        mSampleRate: sampleRate,
        mFormatID: kAudioFormatLinearPCM,
        mFormatFlags: kLinearPCMFormatFlagIsSignedInteger,
        mBytesPerPacket: bytesPerFrame,
        mFramesPerPacket: 1,
        mBytesPerFrame: bytesPerFrame,
        mChannelsPerFrame: numChannels,
        mBitsPerChannel: 16,
        mReserved: 0
    )

    var formatDesc: CMAudioFormatDescription?
    status = CMAudioFormatDescriptionCreate(kCFAllocatorDefault, &asbd, 0, nil, 0, nil, nil, &formatDesc)
    assert(status == noErr)

    var sampleBuffer: CMSampleBuffer?

    // born ready
    status = CMAudioSampleBufferCreateReadyWithPacketDescriptions(
        kCFAllocatorDefault,
        block,      // dataBuffer
        formatDesc!,
        nFrames,    // numSamples
        CMTimeMake(startFrm, Int32(sampleRate)),    // sbufPTS
        nil,        // packetDescriptions
        &sampleBuffer
    )
    assert(status == noErr)

    return sampleBuffer
}

它不会让你对不起，你问过？你真的需要静音 CMSampleBuffer s？你不能通过向前移动演示时间戳将静音插入 AVAssetWriterInput 吗？

Doesn't it make you sorry you asked? Do you really need silent CMSampleBuffers? Can't you insert silence into an AVAssetWriterInput by moving the presentation time stamp forward?

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