MPEG 4 ADTS frame can not have AOT value greater than AAC_LTP. For HE AAC (both v1 and v2) AOT should be set to AAC_LC. Clients are supposed to use implicit SBR signaling to detect presence of SBR. Ref: https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/adtsenc.c#L65 https://developer.apple.com/library/content/technotes/tn2236/_index.html