CMAF Compliant Writing Real Time Sample

Make sure to read my article on AVAssetWriter crashing when using CMAF compliant segments before exploring this sample project.

Minimal sample to demonstrate writing out CMAF compliant segments from a real source fails with an error on Intel macs on Ventura.

The error is in the AVFoundationErrorDomain with code -11800, containing an underlying error in the NSOSStatusErrorDomain with code -16364.

Reproduction conditions

• The AVAssetWriter must be configured with outputFileTypeProfile set to .mpeg4CMAFCompliant.
• The AVAssetWriterInput added to the writer must have expectsMediaDataInRealTime set to true.
• Samples must be appended to the input either:
  • At an variable rate, for example because no new sample is generated when there is no change at the souce (like ScreenCaptureKit does).
  • Frames are delivered significantly faster than 60 FPS.
• The application must run on an Intel mac, Apple Silicon macs are not affected.

Demonstrating the issue

This repository contains a sample app demonstrating the issue:

• Open realtime-cmaf-crash-sample.xcodeproj in Xcode 14.2 or newer on an Intel mac
• Build & run the app
• Hit the "Start" button

After about 5 segments are delivered to the delegate the app will crash.

Workaround

• On the AVAssetWriter change outputFileTypeProfile to mpeg4AppleHLS.
  • Note that this will either produce a different format output.
• On the AVAssetWriterInput set expectsMediaDataInRealTime to false.
  • Might have unexpected side effects dropping frames because isReadyForMoreMediaData might become inaccurate.

Authors

Nonstrict B.V., Mathijs Kadijk & Tom Lokhorst, released under MIT License.