The general rule for the two types of Dolby AAC audio codecs is as follows:
For low bitrate audio 40 kbps to 64 kbps, use HE-AAC @ 44100 Hz
<audio_codec>dolby_heaac</audio_codec>
For high bitrate audio 80 kbps to 320 kbps, use AAC-LC @ 44100 Hz
<audio_codec>dolby_aac</audio_codec>