Movies that lay on their side
Have you ever taken a Portrait oriented movie with your iPhone or iPad and sent it to your friends who were using Windows? I can understand their frustration when the video I so carefully recorded causes them to bend their neck to the side:
So what’s going on here? The problem is that the .MOV file that I send them has a 90 degree rotation set as the preferred transform. Some Windows clients (such as Windows Media Player, VLC media player, etc) do not take this transform into consideration when presenting the video.
The VideoExport Swift Project
I wanted to create a project that would allow me to address the issue with rotations and other compatibility concerns.
I published my results to scottcarter/VideoExport on Github.
Posted in iOS, Objective-C, Swift
Tagged export, mp4, objective c, SDAVAssetExportSession, Swift, video, video bitrate, video composition, video settings, videoComposition, Xcode
This article discusses the techniques I use for bookmarking code and adding log statements for both Objective-C and Swift.
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).
Posted in Objective-C, Swift
Tagged bookmark, debugging, downcast, iOS, logging, macro, objective c, pragma, preprocessor, Swift, Xcode
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.
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).
Posted in iOS
Tagged CGAffineTransform, copyNextSampleBuffer, debugging, error, export, mp4, objective c, SDAVAssetExportSession, video, video composition, video settings, videoComposition, Xcode
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.
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