(2018-04-10, 06:19)puunda Wrote: Hi everyone,
I've noticed that a lot of what I'm download has AAC audio. I've set things up so it converts it to DD. This is fine up to 5.1, but 7.1 AAC will only get encoded as 5.1 DD.
You are transcoding multichannel AAC to DD. DD is limited to 5.1 max, so that is the best you can do with a DD transcode.
If the Mi box supports PCM multichannel output you would be better off setting your channel output to 7.1 and disabling DD transcode. This will get your Mi box to decode the AAC 7.1 to PCM 7.1 and output it as PCM multichannel 7.1 over HDMI.
The same is also true for FLAC multichannel content
Quote:I'm not sure when AAC became popular, but my question is, is there any way to stream 7.1 AAC properly?
AAC (like FLAC) is a popular file-based codec, but has never been an optical disc standard AFAIK. The Consumer electronics industry who standardise HDMI standards and Home Cinema Amp manufacturers are still geared up to supporting optical disk players for bit streaming, and these platforms define the codecs that they support. (DD, DTS, DD+, Dolby True HD, DTS HD MA/HRA, DD + with Atmos, Dolby True HD with Atmos, DTS:x)
A very small number of amps DID support WMA bit streaming. No amp AFAIK has ever supported AAC bitstreaming and I don't think it is standardised for HDMI or SPDIF carriage. (For a while, in the early days, there was a confusion option to enable AAC bitstreaming in XBMC - may have been pre-Kodi - but it was non-functional, as it couldn't ever be functional!)
Quote:I'm assuming my AVR (Onkyo) won't accept multi channel AAC, this is why it gets converted to DD?
No amp accepts AAC over HDMI (or SPDIF) AFAIK
It gets converted to DD because you probably have enable transcode to DD enabled in your Kodi audio settings? if you didn't it would be decoded to PCM.
Quote:Is there any way to converting it to 7.1 DD?
No - because DD7.1 doesn't exist. DD is limited to 5.1 (possibly a niche 6.1 with some matrix surround extensions - or was that only DTS EX ?)
Quote:Why does 7.1 AAC exist? In what situation can you play it 7.1?
On any amp with a multichannel PCM input - any amp that supports HD Audio will almost certainly support 5.1/7.1 PCM output.
AIUI AAC is a more modern codec, so may well deliver higher audio quality at lower bitrates than Dolby Digital. AAC 5.1 is used for broadcast TV in the UK because Dolby Digital didn't support an audio description receiver-mix solution in bandwidth efficient manner when we introduced OTA HDTV in 2009, and TVs can't receiver mix two different codecs cost effectively (or that was the reason given)
It's used for other platforms because it doesn't require a Dolby licence. This is really important for devices like mobile phones, tablets etc. I know mobiles don't output 5.1 - but staying with a single codec does make sense. AAC stereo is a common codec for streaming and file playback, so sticking with AAC for multichannel makes sense commercially AIUI.