according to the specification the default channel layout for 7.1 channels in AAC/ALAC is 7.1(wide) or SDDS (L R C LFE BL BR FCL FCR).
This layout won‘t get much support on modern devices like my Yamaha Receiver.
Does someone know what happens when the audio stream is processed by e.g. my Apple TV?
AAC/ALAC 7.1 SDDS (Apple TV) —> PCM 7.1 (L R C LFE BL BR SL SR) (Receiver)
AAC/ALAC 7.1 SDDS (Apple TV) —> PCM 7.1 SDDS (Receiver) (and Receiver looks for SR and SL so in fact he gets 6 channels)
I tested it.
FCL and FCR getting mapped correctly.