Dolby Atmos


#1

As we all know, the Vero 4K has a function to downsample HD multichannel audio to older formats like 5.1 Dolby Digital and DTS.

At times this function was very useful for me because my receiver only decodes 5.1 Dolby Digital (AC3) and DTS. However, whenever possible I try to get movies with Dolby Atmos track so that I can enjoy it when I upgrade to a Atmos system.

In earlier versions of the Vero 4K firmware, the downsample from Atmos to 5.1 AC3 was done without problems, however, since an update months ago (I can not tell when), the downsample is made for only 2.0 channels.

So I wonder if anyone else has noticed this problem, and what solutions this might have. I did not want to downgrade firmware because the newer versions added features like HDR quality improvement, etc.


#2

Hi,

First thing: can you go to My OSMC and upload a set of logs so we can check your audio settings are correct?

Thanks

Sam


#3

I finally managed to do this.

https://paste.osmc.tv/jeyeyobuca


#4

In your log I can see that you haven’t got AC3 transcoding enabled…


#12

In the Settings -> System -> Audio, I have selected (active) the option “Allow Passthrough”, and then, “Dolby Digital (AC3) capable receiver” and “DTS capable receiver”. Something is missing?


#13

As you’ve selected 5.1 output channels (this setting only takes effect for PCM output), the AC3 transcoding option isn’t visible for you. Assuming that your audio receiving device only processes 2.0 channel PCM as well as DTS and Dolby Digital, please set your audio settings to the following:

Audio device: PCM or HDMI
Number of channels: 2.0
Output configuration: Best match
Passthrough: enabled
DTS/AC3 passthrough: enabled
DTS-HD/TrueHD/E-AC3 passthrough: disabled
AC3 transcoding: enabled


#14

Even with these settings, the option AC3 transcoding does not appear…


#15

Have you set channels to 2.0? In your log we can see that you’ve set them to 5.1


#16

Indeed – the option will only appear when the # of channels is set to 2.0.


#17

Yes, I did. But I figured out to find that option. So, this may fix my problem?

https://paste.osmc.tv/udayuduzem


#18

That looks good. Is the resulting audio output confirming it?


#19

Only tomorrow I’ll be able to confirm that. Thank you for now for the help!


#20

Finally I was able to test the settings that Chillbo indicated, and yes, everything is working as it was supposed to be. Thank you Chillbo and sam_nazarko!


#21

Good stuff.


#22

From a technical perspective is it easy to strip TrueHD down to DD+ and/or DD without first decoding then re-encoding? Likewise, can one strip DD+ into DD without much extra processing?


#23

A TrueHD track might have a lossy stream (Dolby Digital or DD+) muxed in with it, and in that case, it’s easy to get to the lossy part. But, doing it that way isn’t much different from having a bare TrueHD track with a separate DD track. There is no real relationship between the TrueHD and lossy part when muxed into the same track, unlike DTS-HD, which has a core that is required to be decoded to also decode the HD part. So, sometimes, it’s easy, but other times a decode/encode is required. Since TrueHD is lossless, and it really doesn’t take much CPU to decode, it’s not a big deal, although the re-encode can take a bit more CPU.

Dolby Digital (AC-3) and Dolby Digital Plus (E-AC-3) are two completely different codecs. Like a TrueHD track, an E-AC-3 track can contain an AC-3 substream, but, again, it does not have to be related to the E-AC-3, and is not required. A “bare” E-AC-3 stream is enough to be a compliant E-AC-3 track. So, this also would require a decode/re-encode.


#24

I was under the impression that a TrueHD track is just that and a second DD track is required by Blu-ray standards.
So if a Blu-rau has Dolby TrueHD it is required to also have a DD track.
They are seperate tracks, but a stand alone player will default to what your set up supports so it’s pretty seamless.
With a Vero, you would have to choose the secondary track to get DD.
DTS-HD has the lossy core built in to it so it’s nor required to have a separate track.
When I remux videos that have TrueHD, I don’t bother bringing the DD track along even though my sound bar doesn’t support TrueHD.
The Vero does a great job at transcoding it on the fly.
I prefer the DTS-HD MA tracks when they are available (personal preference).

From wikipedia:
In the Blu-ray Disc specification, Dolby TrueHD is an optional codec. Dolby TrueHD audiotracks may carry up to 8 discrete audio channels (7.1 surround) and 20 objects of 24-bit audio at 96 kHz or up to 6 channels (5.1 surround) at 192 kHz.[1] The maximum encoded bitrate is 18 Mbit/s. Since Dolby TrueHD is an optional codec, a companion Dolby Digital bitstream (2.0 192kbit/s or 5.1 448kbit/s/640kbit/s) must accompany the Dolby TrueHD bitstream on Blu-ray discs. Blu-ray Disc players consider this combination of two audio bitstreams as a single logical audio track, and a Blu-ray Disc player will automatically select the Dolby Digital or Dolby TrueHD bitstream depending on its decoding and/or bitstreaming capabilities.


#25

Or might I suggest our wiki? :yum:


#26

When this standard was set, Dolby and disc manufacturers decided it meant that users shouldn’t have to even make a decision, so the Dolby Digital stream was muxed into TrueHD stream to make a single track. Decoders that understood TrueHD would ignore the Dolby Digital, and decoders that didn’t would ignore the TrueHD, and the user wouldn’t have to even think about what their equipment supported.

Once UHD discs were released, the standard was relaxed, and now a completely separate Dolby Digital track is acceptable to meet the standard.


#27

Can you give an example of a Blu-ray that is not UHD but has TrueHD and DD as a single track as you have alluded to?
I’ve never come across this.