Tag Archives: debugging

Thinking outside the box to debug: Charles Proxy, push and a forced crash

An issue on just one device

A couple of weeks ago, one of my colleagues reported that she found an issue with the iOS app for AAFES EXTRA, an app that I had developed for BlueSoHo for their client The Army & Air Force Exchange Service.

The iOS app was not displaying the expected updated content.  The Android app was working fine.  To make things more difficult, the problem was only occurring on one specific device and could not be replicated on any other devices, even of the same model.

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Crashlytics download issue and provisioning profile debug

Unable to Download App

I was asked to fix an issue with an existing  app called SmartPak wherein users on iOS 10.1+ would see a warning message about the app slowing down their phone if they were using a 64 bit device.   The fix itself was pretty straightforward – the architecture settings did not support 64 bit builds and a Digimarc library needed to be updated.

As I prepared to distribute the app for internal QA, I ran into a more difficult problem.  I was unable to download the Adhoc Crashlytics build to any of my test devices.


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Logging and bookmarks with Objective-C and Swift


This article discusses the techniques I use for bookmarking code and adding log statements for both Objective-C and Swift.


Temporary Bookmarks

When I develop code I often find a need to temporarily reference different sections that I’m working on, either within the same file or in many different files.   Prior to Xcode 4 there was apparently a means to set and jump to bookmarks with keyboard shortcuts as mentioned in the article Killer Xcode Tips and Tricks – Tips 1 to 10 (see tips 7 and 8).

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Using a video composition to process certain videos causes an Xcode simulator hang

Video Export Project

I am working on a project that will process videos taken with the camera or pulled from the Photo Library and export them to MP4 format, reducing the dimensions and bit rate.

As part of this process I am using the code for SDAVAssetExportSession that is a AVAssetExportSession drop-in replacement with customizable audio and video settings.

Video Composition

I make use of an instance of AVAssetReaderVideoCompositionOutput that is added to AVAssetReader in SDAVAssetExportSession.m.  I set the videoComposition property of the former instance to a composition that allows me to set the render size and some appropriate transforms for scaling, etc. (CGAffineTransform).

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Xcode simulator bug with Swift to Objective-C call passing CMTime structure

CMTime Bug

I was in the process of creating an illustrative Swift project that performed some video conversions when I ran across an interesting bug.

The bug first manifested itself when I was attempting to set the opacity of a AVMutableVideoCompositionLayerInstruction object as part of a method that was creating a AVVideoComposition object.

videolayerInstruction.setOpacity(0.0, atTime: mytime)

Here mytime is a CMTime structure that is the AVAsset duration.

When I ran this on the simulator, I got an exception with the message “The time of an opacity setting must be numeric.”

Debugging the error

After searching Google and the Apple Developer forums, I could not find any reference to my error message or any issue related to CMTime in this context.

Since I had used similar code in Objective-C, I started the process to narrow down the error.  I first attempted to call a simple Objective-C method from Swift that would set the opacity (passing in videolayerInstruction as first arg and mytime as second arg).    This provoked the same error.  I discovered that the CMTime structure was corrupted in the Objective-C method.

Through trial and error I found that the corruption would not occur if I reversed the order of the arguments to the Objective-C call.    Corruption also did not happen if I passed the structure by reference.    A different structure type (I used CGSize) also did not encounter any corruption.

Specific situation

The end result of my investigation was that the error that I was seeing only occurred under very specific circumstances.  In particular:

  • Only with Swift to Objective C call.
  • Only on simulator with iPhone 4S and iPhone 5 configurations.
  • CMtime structure passed as second argument.

I suspect that the underlying issue may be a 32 bit versus 64 bit consideration since the iPhone 5S was the first device to introduce 64 bit processing.

Bug report and Github example project

An Apple bug report was filed today.   An example project has been uploaded to Github at https://github.com/scottcarter/CMTimeBug