Though m4a audio files might be more efficient, there are still many issues even when trying to play on an iPhone, the most annoying being that QuickTime (the standard player called from non-built-in apps) stops to play an m4a when not in foreground. Hence I need mp3 for audio-only export. I learnt from support that mp3 still can be produced in Camtasia2019 using the "Share | Export audio only" path (it is not possible using the production wizard - why?) for Win 8.1 and 10. Though this is better than nothing, the export is fixed to 256kBit, producing huge files - especially when exporting something like a podcast. I searched the project files for a possible option to no avail. Please make some bit rates available to choice, maybe "Speech (64kBit), Standard (128kBit), High (256kBit)".