I have a problem: I always was able to export audio files i recorded in quicktime through the "Audio Only" option in File - Export with at least 256 kbit/s AAC. When i do the same now it only produces a 128 kbit/s file.
Just checked my system and it still records audio normally (at 256+ Kbps). Would assume one or more of the following:
1) You or one of your apps has modified the system audio settings. (Believe default is 24-bit @ 44.1KHz.)
2) Your recording workflow (input device) is choking the data rate.
3) Your OS and/or QT X Player app is corrupted or conflicted with some hardware peripheral or software app.
I haven't found an option to change the export settings in Quicktime. Is it even possible to change them since Quicktime doesn't offer any possibilities to change the quality of export?
Input/Output system settings for different devices is/are controlled by the Audio MIDI Setup.app utility. (I normally don't recommend changing the default settings as it may adversely impact the operation of some apps which depend on the default settings.) Not sure if it still holds true, but simply opening and closing the GarageBand app used to automatically reset these settings under much older operating systems.
Since you did not provide any information regarding a specific workflow, I would probably recommend running a secondary check (temp workaround) of your QT X audio recording capability. Try using the "Maximum" Quality QT X record setting. It should produce 16-bit, 24-bit, or 32-bit (approximately 1.6 Mbps, 2.1Mbps, or 2.8 Mbps data rate) 44.1 KHz LPCM file if working properly depending on specific workflow/input device. This file can then be converted to data rate targeted M4A files using the built-in Sierra Finder "Encode" service feature settings—Speech Podcast (approx 48-64 Kbps @ 22.5 KHz), High Quality (approx 96-128 Kbps @ 44.1 KHz), iTunes Plus (approx 256-320 Kbps @ 44.1 KHz), or Apple Lossless (approx 1024 Kbps @ 44.1 KHz).
Another workaround you may wish to try while you are trying to solve the current QT export issue would be to use a different app like GarageBand. GarageBand also records as LPCM interim content but has built-in "Share" options that allow you to export files to specific 64, 128, 192, or 256 Kbps AAC or MP3 audio files or 16-/24-bit LPCM (AIFF) files.
