Question

此代码会导致内存泄漏和应用崩溃：

    var outputSamples = [Float]()

    assetReader.startReading()
    while assetReader.status == .reading {
        let trackOutput = assetReader.outputs.first!

        if let sampleBuffer = trackOutput.copyNextSampleBuffer(),
            let blockBuffer = CMSampleBufferGetDataBuffer(sampleBuffer) {
            let blockBufferLength = CMBlockBufferGetDataLength(blockBuffer)
            let sampleLength = CMSampleBufferGetNumSamples(sampleBuffer) * channelCount(from: assetReader)
            var data = Data(capacity: blockBufferLength)
            data.withUnsafeMutableBytes { (blockSamples: UnsafeMutablePointer<Int16>) in
                CMBlockBufferCopyDataBytes(blockBuffer, atOffset: 0, dataLength: blockBufferLength, destination: blockSamples)
                CMSampleBufferInvalidate(sampleBuffer)

                let processedSamples = process(blockSamples,
                                               ofLength: sampleLength,
                                               from: assetReader,
                                               downsampledTo: targetSampleCount)
                outputSamples += processedSamples
            }
        }
    }
    var paddedSamples = [Float](repeating: silenceDbThreshold, count: targetSampleCount)
    paddedSamples.replaceSubrange(0..<min(targetSampleCount, outputSamples.count), with: outputSamples)

这是由于copyNextSampleBuffer()和The Create Rule造成的。

反过来，我们不能在Swift中使用CFRelease（）。我之所以无法理解为何仅与Objective-C规则相关联。

是否可以在Swift中手动释放CMSampleBuffer？

Answer 1

我最近通过使用自动释放池解决了类似的问题

尝试包装自动释放池中使用sampleBuffer的区域。像这样：

var outputSamples = [Float]()

assetReader.startReading()
while assetReader.status == .reading {
    let trackOutput = assetReader.outputs.first!

    autoreleasepool {
        if let sampleBuffer = trackOutput.copyNextSampleBuffer(),
            let blockBuffer = CMSampleBufferGetDataBuffer(sampleBuffer) {
            let blockBufferLength = CMBlockBufferGetDataLength(blockBuffer)
            let sampleLength = CMSampleBufferGetNumSamples(sampleBuffer) * channelCount(from: assetReader)
            var data = Data(capacity: blockBufferLength)
            data.withUnsafeMutableBytes { (blockSamples: UnsafeMutablePointer<Int16>) in
                CMBlockBufferCopyDataBytes(blockBuffer, atOffset: 0, dataLength: blockBufferLength, destination: blockSamples)
                CMSampleBufferInvalidate(sampleBuffer)

                let processedSamples = process(blockSamples,
                                               ofLength: sampleLength,
                                               from: assetReader,
                                               downsampledTo: targetSampleCount)
                outputSamples += processedSamples
            }
        }
    }
}
var paddedSamples = [Float](repeating: silenceDbThreshold, count: targetSampleCount)
paddedSamples.replaceSubrange(0..<min(targetSampleCount, outputSamples.count), with: outputSamples)

如果我理解正确，一旦它移出autoreleasepool的范围，sampleBuffer将被释放

Answer 2

这并不是真正的解决方案，因为似乎无法手动释放内存，并且将while循环与assetReader结合使用会导致在读取不安全的可变字节时不会释放内存。

此问题已通过一种解决方法解决：将音频文件转换为CAF格式，然后再将其暴露给while循环。

缺点：需要花费很长时间，音频文件越长-花费的时间越多。

上行：它只使用了很小的内存，这首先就是问题。

灵感来自：https://stackoverflow.com/users/2907715/carpsen90的Extract meter levels from audio file答案

如何手动释放CMSampleBuffer

2 个答案: