The AAC encoder does not require the `MF_MT_USER_DATA` attribute, if it's missing it will simply generate one from other attributes.
Sure, but that shouldn't require doing anything manually, right? We just need to query the codec_data that's set as caps on our sink pad. That'll require some code changes, but they'd be less awkward than reconstructing the codec_data from parsed data...
Unless the native AAC encoder doesn't actually set that attribute?