swift 。获取 CMAudioFormatDescription 时的 EXC_BREAKPOINT

Question

我正在尝试从音频文件中检索采样率和 channel 数。 我在此行遇到运行时“EXC_BREAKPOINT (code=EXC_ARM_BREAKPOINT)”错误:

let audioFormstDesc = descriptions[0] as CMAudioFormatDescription

这是我使用的最简单的代码版本:

import AVFoundation
import CoreMedia
import MediaPlayer

class ViewController: UIViewController
{
    override func viewDidLoad()
    {
        super.viewDidLoad()

        let query = MPMediaQuery.songsQuery()
        let song = query.items[0] as MPMediaItem
        let url = song.valueForProperty(MPMediaItemPropertyAssetURL) as NSURL
        let songAsset = AVURLAsset.URLAssetWithURL(url, options: nil)
        let trackAsset = songAsset.tracks[0] as AVAssetTrack
        if let descriptions = trackAsset.formatDescriptions
        {
            let audioFormstDesc = descriptions[0] as CMAudioFormatDescription
            let streamBasicDescription = CMAudioFormatDescriptionGetStreamBasicDescription(audioFormstDesc)
        }
    }
}

在 Objective-C 中，这段代码工作得很好:

MPMediaQuery *query = [MPMediaQuery songsQuery];
MPMediaItem *song = [[query items] objectAtIndex:0];
NSURL *url = [song valueForProperty: MPMediaItemPropertyAssetURL];
AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:url options:nil];
AVAssetTrack *trackAsset = songAsset.tracks[0];

UInt32 sampleRate = 0, channelCount = 0;
NSArray* descriptions = trackAsset.formatDescriptions;
CMAudioFormatDescriptionRef audioFormstDesc = (__bridge CMAudioFormatDescriptionRef)descriptions[0];
const AudioStreamBasicDescription* audioStreamDesc = CMAudioFormatDescriptionGetStreamBasicDescription(audioFormstDesc);
if(audioStreamDesc)
{
    sampleRate = audioStreamDesc->mSampleRate;
    channelCount = audioStreamDesc->mChannelsPerFrame;
}

println(descriptions[0]) 打印到控制台:

<CMAudioFormatDescription 0x15d3b690 [0x387e5ad0]>

如何处理该错误？

Answer 1

在 Swift 和 xcode 6 beta 中，如果您使用“swift 优化级别”-O(最快)进行编译，有时会出现这种错误。尝试在“build设置”中将优化级别设置为 -Onone。