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CMFormatDescription.audioStreamBasicDescription has wrong or unexpected sample rate for audio channels with different sample rates
In my app I use AVAssetReaderTrackOutput to extract PCM audio from a user-provided video or audio file and display it as a waveform. Recently a user reported that the waveform is not in sync with his video, and after receiving the video I noticed that the waveform is in fact double as long as the video duration, i.e. it shows the audio in slow-motion, so to speak. Until now I was using CMFormatDescription.audioStreamBasicDescription.mSampleRate which for this particular user video returns 22'050. But in this case it seems that this value is wrong... because the audio file has two audio channels with different sample rates, as returned by CMFormatDescription.audioFormatList.map({ $0.mASBD.mSampleRate }) The first channel has a sample rate of 44'100, the second one 22'050. If I use the first sample rate, the waveform is perfectly in sync with the video. The problem is given by the fact that the ratio between the audio data length and the sample rate multiplied by the audio duration is 8, double the ratio for the first audio file (4). In the code below this ratio is given by Double(length) / (sampleRate * asset.duration.seconds) When commenting out the line with the sampleRate variable definition in the code below and uncommenting the following line, the ratios for both audio files are 4, which is the expected result. I would expect audioStreamBasicDescription to return the correct sample rate, i.e. the one used by AVAssetReaderTrackOutput, which (I think) somehow merges the stereo tracks. The documentation is sparse, and in particular it’s not documented whether the lower or higher sample rate is used; in this case, it seems like the higher one is used, but audioStreamBasicDescription for some reason returns the lower one. Does anybody know why this is the case or how I should extract the sample rate of the produced PCM audio data? Should I always take the higher one? I created FB19620455. let openPanel = NSOpenPanel() openPanel.allowedContentTypes = [.audiovisualContent] openPanel.runModal() let url = openPanel.urls[0] let asset = AVURLAsset(url: url) let assetTrack = asset.tracks(withMediaType: .audio)[0] let assetReader = try! AVAssetReader(asset: asset) let readerOutput = AVAssetReaderTrackOutput(track: assetTrack, outputSettings: [AVFormatIDKey: Int(kAudioFormatLinearPCM), AVLinearPCMBitDepthKey: 16, AVLinearPCMIsBigEndianKey: false, AVLinearPCMIsFloatKey: false, AVLinearPCMIsNonInterleaved: false]) readerOutput.alwaysCopiesSampleData = false assetReader.add(readerOutput) let formatDescriptions = assetTrack.formatDescriptions as! [CMFormatDescription] let sampleRate = formatDescriptions[0].audioStreamBasicDescription!.mSampleRate //let sampleRate = formatDescriptions[0].audioFormatList.map({ $0.mASBD.mSampleRate }).max()! print(formatDescriptions[0].audioStreamBasicDescription!.mSampleRate) print(formatDescriptions[0].audioFormatList.map({ $0.mASBD.mSampleRate })) if !assetReader.startReading() { preconditionFailure() } var length = 0 while assetReader.status == .reading { guard let sampleBuffer = readerOutput.copyNextSampleBuffer(), let blockBuffer = sampleBuffer.dataBuffer else { break } length += blockBuffer.dataLength } print(Double(length) / (sampleRate * asset.duration.seconds))
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118
Aug ’25
How to install macOS Tahoe 26 on an external drive
In the past I was always able to install every major macOS version on an external drive so that I can test my apps. But now I'm unable to install macOS Tahoe 26 on an external drive. Actually, as far as I'm aware, there are not even official links to macOS 26 installers, but only instructions on how to update to macOS 26 from an existing macOS installation. So I thought I'd install macOS 15 on a separate drive and then update to macOS 26, but whenever I run the macOS 15 installer, tell it to install on the external drive, and reboot after the setup process completes, my MacBook just boots into my main macOS partition as if nothing happened. 3 months ago I somehow managed to install macOS Tahoe beta 1 on an external drive, I don't remember how (but I don't think it was anything crazy); booting into that beta 1 partition and trying to update doesn't work either, as my MacBook again boots into my main macOS partition. I already asked help about the update problem one month ago here, but nobody replied. Could someone at Apple please provide instructions on how one is supposed to install macOS 26 on an external drive (if possible before it becomes available to the public)? Are we supposed to buy a separate Mac for every macOS version that we want to test our apps on?
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180
Sep ’25
Tapping tab item in Xcode UI test doesn't always work
While preparing automated screenshots with Xcode UI tests for the iOS 26 release, I noticed that this simple line of code app.buttons["myTabItem"].tap() doesn't always work, both on iPhone and iPad Simulator. In fact, it rarely works. Even when repeating the same test, mostly it fails on that line, but a few times it works and I can see the tab item change in the simulator. My main view looks like this: TabView { MyTab1() .tag(tag1) .tabItem { Label("label1", systemImage: "image1") } MyTab2() .tag(tag2) .tabItem { Label("label2", systemImage: "image2") .accessibilityIdentifier("myTabItem") } The error I get is Failed to tap "myTabItem" Button: No matches found for Elements matching predicate '"myTabItem" IN identifiers' from input In the given list of buttons, I see the tab items with their labels, but none of them seem to have an identifier, while other buttons have the correct identifier. I wonder how this can only sometimes work. I tried isolating the issue by iteratively commenting out parts of the SwiftUI code, but unfortunately the behaviour seems erratic. When a change results in the issue not happening anymore, undoing the last X changes often causes the issue to stay away, even with configurations that previously had the issue. I've already spent almost a whole day trying to find the root cause, but with such apparently random behaviour it has proven impossible. Of course, I cannot reproduce the issue with a fresh test project, so the only way to reproduce it with 95% probability is running my original project. Has anyone had the same issue, or does anyone know how I could debug this to find out what causes my UI test to not be able to tap another tab item?
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174
Sep ’25
NSWindow.titlebarAppearsTransparent only works after collapsing and expanding sidebar
I'm using the simplified code below to create a window with 4 split view items, some of them collapsed. I would expect the title bar to be transparent since I'm using window.titlebarAppearsTransparent = true, but it seems that this particular view configuration causes the title bar to be visible until I collapse and expand the sidebar again. Removing any of the split view items, uncollapsing any of them, or changing the view of any of the view controllers, causes the title bar to be consistently visible or hidden, although I don't understand the logic, since I'm telling the window that it should be transparent. When launching the app in light mode, it's more difficult to notice the issue since the title bar background is equal to the content background and only the separator is visible (even though the code sets window.titlebarSeparatorStyle = .none): After collapsing and expanding the sidebar, the separator is gone: In dark mode the title bar is more visible: After collapsing and expanding the sidebar, the title bar background and separator are gone: I created FB20306872. @main class AppDelegate: NSObject, NSApplicationDelegate, NSToolbarDelegate { var splitViewController: NSSplitViewController! func applicationDidFinishLaunching(_ aNotification: Notification) { let splitViewItem1 = NSSplitViewItem(sidebarWithViewController: ViewController1()) let splitViewItem2 = NSSplitViewItem(viewController: ViewController2()) let splitViewItem3 = NSSplitViewItem(viewController: NSViewController()) splitViewItem3.isCollapsed = true let splitViewItem4 = NSSplitViewItem(viewController: NSViewController()) splitViewItem4.isCollapsed = true splitViewController = NSSplitViewController() splitViewController.splitViewItems = [splitViewItem1, splitViewItem2, splitViewItem3, splitViewItem4] let window = NSWindow(contentViewController: splitViewController) window.styleMask = [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView] window.titlebarAppearsTransparent = true let toolbar = NSToolbar(identifier: "") toolbar.delegate = self toolbar.displayMode = .iconOnly window.toolbar = toolbar window.titlebarSeparatorStyle = .none window.makeKeyAndOrderFront(nil) } func toolbarAllowedItemIdentifiers(_ toolbar: NSToolbar) -> [NSToolbarItem.Identifier] { return [.space, .flexibleSpace, .sidebarTrackingSeparator, .init("item")] } func toolbarDefaultItemIdentifiers(_ toolbar: NSToolbar) -> [NSToolbarItem.Identifier] { return [.init("item"), .sidebarTrackingSeparator] } func toolbar(_ toolbar: NSToolbar, itemForItemIdentifier itemIdentifier: NSToolbarItem.Identifier, willBeInsertedIntoToolbar flag: Bool) -> NSToolbarItem? { switch itemIdentifier.rawValue { case "item": let item = NSToolbarItem(itemIdentifier: itemIdentifier) item.image = NSImage(systemSymbolName: "sidebar.leading", accessibilityDescription: nil) item.action = #selector(toggleSidebar(_:)) item.target = self return item default: return nil } } @objc func toggleSidebar(_ sender: Any?) { splitViewController.splitViewItems[0].animator().isCollapsed = !splitViewController.splitViewItems[0].isCollapsed } } class ViewController1: NSViewController { override func loadView() { view = NSView(frame: CGRect(x: 0, y: 0, width: 300, height: 200)) } } class ViewController2: NSViewController { override func loadView() { let textView = NSTextView() let scrollView = NSScrollView(frame: CGRect(x: 0, y: 0, width: 400, height: 200)) scrollView.hasVerticalScroller = true scrollView.documentView = textView view = scrollView } }
Topic: UI Frameworks SubTopic: AppKit Tags:
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81
Sep ’25
App icon produced by Xcode 26 is 1 MB bigger than Xcode 16
When comparing the Assets.car file of the previous and current versions of my app, compiled with Xcode 16 and 26, respectively, with the Terminal command assetutil --info MyApp.app/Contents/Resources/Assets.car I see that the new version contains many more app icons at different sizes, increasing my app's size by 1 MB (not much, but considering that the app is only 6 MB in total...): { "AssetType" : "MultiSized Image", "Name" : "AppIcon", "NameIdentifier" : 6849, "Scale" : 1, "SHA1Digest" : "9D75F76992E9E9E5531A214A4AE282EBD381F7EB903024E00FB25EB42381CC45", "SizeOnDisk" : 308, "Sizes" : [ "16x16 index:1 idiom:universal", "32x32 index:2 idiom:universal", "64x64 index:3 idiom:universal", "128x128 index:4 idiom:universal", "256x256 index:5 idiom:universal", "512x512 index:6 idiom:universal", "1024x1024 index:7 idiom:universal" ] } The previous one allowed me to add only two sizes: { "AssetType" : "MultiSized Image", "Name" : "AppIcon", "NameIdentifier" : 6849, "Scale" : 1, "SHA1Digest" : "AC782A2FFF9A4B2D563EF64DF41A179583440560F8732A176A8376B31000368E", "SizeOnDisk" : 248, "Sizes" : [ "256x256 index:1 idiom:universal", "512x512 index:2 idiom:universal" ] } Is there a way to only ship the strictly necessary app icons sizes while using Xcode 26 Icon Composer, or will all the sizes be required going forward?
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142
Oct ’25
Feedbacks get closed if they cannot be reliably reproduced
It’s very frustrating when in a feedback I specify that I cannot reliably reproduce it and the feedback gets closed with the message “Since this issue cannot be reproduced, this report has been closed”, e.g. FB18985938. Is Apple not interested in hearing about issues that cannot be reliably reproduced? Many issues unfortunately depend on a variety of factors and it’s often impossible for third-party developers or users to figure out how to reliably reproduce them. Usually these kind of issues get addressed by e.g. adding more logging so that the next time it happens it's easier to find out what's causing it. Then the last part of the message “Please file a new report with a sysdiagnose if you encounter this issue again” sounds like I’m being teased, because what use is a new sysdiagnose if I still cannot reproduce it reliably? It will just be closed like the last one. I created FB20595673 for this issue.
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89
Oct ’25
API to copy files like the Finder does with progress information
I regularly receive emails from my customers asking why my app, which copies files from a source folder to a destination folder, gives an error during the copy operation, usually when some kind of NAS is involved. I then ask if copying the same file works in the Finder and they usually say yes. Then it’s up to me to contact the NAS vendor and ask why their NAS doesn’t work correctly with the copyfile function which my app uses to copy files, and provide them with a sample Xcode project that reproduces the issue. It would be so much easier for me, and probably other developers as well, if my customers could test their NAS with the Finder, then if it doesn’t work, contact their NAS vendor and solve the issue, or if it works, rest assured that file copies will work for any other app that uses the same API as the Finder. I could spend my time doing much more productive and interesting work rather than checking why every other NAS doesn’t work with my app which, after all, uses the most basic file copy mechanism available on macOS. Is there any chance that in the future (hopefully sooner than later) there will be an API to copy files like the Finder with progress information, or is there a reason why this won't ever be possible? I created FB20929181.
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39
Nov ’25