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Shield Transcoding DTS audio

nvidia shield transcode

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#1 D34DC3N73R OFFLINE  

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Posted 24 March 2019 - 03:46 PM

The Nvidia Shield should be able to direct play this audio, but it is forcing a transcode due to "unsupported audio". For reference, the same file direct plays using Plex. Server version 4.1.0.16 beta, Emby Android TV version 1.6.98g. Please let me know if any other info is required here.

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#2 Luke OFFLINE  

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Posted 24 March 2019 - 10:08 PM

Ok, can we look at an example playback session? Please attach the information requested in how to report a media playback issue. thanks !



#3 D34DC3N73R OFFLINE  

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Posted 24 March 2019 - 10:27 PM

server log and the transcode log are attached to the OP am I missing something?



#4 Luke OFFLINE  

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Posted 25 March 2019 - 01:54 AM

Did you enable the audio downmix option in the app's settings?



#5 ebr OFFLINE  

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Posted 25 March 2019 - 11:55 AM

What is your outboard audio equipment and how is it connected?

 

The system is not reporting support for DTS audio.



#6 D34DC3N73R OFFLINE  

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Posted 26 March 2019 - 06:06 PM

If I enable downmix to stereo, the video/audio will direct play. However, I'd like to keep the 5.1 channels if possible.

 

The Shield is HDMI to my TV. I use HDMI ARC from the TV to a Polk audio magnifi soundbar. This did get me thinking though, I use passthrough audio in plex, which is maybe why I don't have issues with DTS. Does emby have something similar that could be enabled?



#7 MRobi OFFLINE  

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Posted 26 March 2019 - 06:25 PM

If I enable downmix to stereo, the video/audio will direct play. However, I'd like to keep the 5.1 channels if possible.

 

The Shield is HDMI to my TV. I use HDMI ARC from the TV to a Polk audio magnifi soundbar. This did get me thinking though, I use passthrough audio in plex, which is maybe why I don't have issues with DTS. Does emby have something similar that could be enabled?

From looking at your first image it appears the audio profile is DTS-HD Master Audio. HDMI-ARC does not support DTS-HD, not enough bandwidth available. I may be mistaken but I don't believe the polk soundbars support the newer DTS-HD format either. 



#8 D34DC3N73R OFFLINE  

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Posted 26 March 2019 - 07:06 PM

From looking at your first image it appears the audio profile is DTS-HD Master Audio. HDMI-ARC does not support DTS-HD, not enough bandwidth available. I may be mistaken but I don't believe the polk soundbars support the newer DTS-HD format either. 

 

If I'm not mistaken, DTS-HD MA is backward compatible with DTS capable receivers/soundbars. DTS-HD MA audio should play as DTS. 

 

https://en.wikipedia...HD_Master_Audio

 

 

According to the DTS-HD White Paper,[9] DTS-HD Master Audio contains 2 data streams: the original DTS core stream and the additional "residual" stream which contains the "difference" between the original signal and the lossy compression DTS core stream. The audio signal is split into two paths at the input to the encoder. One path goes to the core encoder for backwards compatibility and is then decoded. The other path compares the original audio to the decoded core signal and generates residuals, which are data over and above what the core contains that is needed to restore the original audio as bit-for-bit identical to the original. The residual data is then encoded by a lossless encoder and packed together with the core. The decoding process is simply the reverse.


#9 MRobi OFFLINE  

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Posted 26 March 2019 - 07:18 PM

If I'm not mistaken, DTS-HD MA is backward compatible with DTS capable receivers/soundbars. DTS-HD MA audio should play as DTS. 

 

https://en.wikipedia...HD_Master_Audio

Yes, it is backwards compatible, but it still needs to be connected in a way that can support the throughput of data. It sends the full signal and then your receiver decodes the information. HDMI-ARC lacks that ability.

 

As a test, you can try plugging your shield directly to your soundbar and seeing if it will play that way. I still suspect you'll get remuxed audio though if the polk doesn't support DTS-HD.



#10 D34DC3N73R OFFLINE  

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Posted 26 March 2019 - 07:25 PM

Yes, it is backwards compatible, but it still needs to be connected in a way that can support the throughput of data. It sends the full signal and then your receiver decodes the information. HDMI-ARC lacks that ability.

 

As a test, you can try plugging your shield directly to your soundbar and seeing if it will play that way. I still suspect you'll get remuxed audio though if the polk doesn't support DTS-HD.

 

Any guesses on how Plex is able to achieve 5.1 playback using the same file without transcoding audio?

 

And further down the wiki page
 

 

DTS-HD Master Audio may be transported to AV receivers in 5.1, 6.1 or 7.1 channels, at lossless quality, in one of three ways depending on player and/or receiver support:[9]

  • Over 6, 7 or 8 RCA connectors as analog audio (not lossless), using the player's internal decoder and digital-to-analog converter (DAC).
  • Over HDMI 1.1 (or higher) connections as 6-, 7- or 8-channel linear PCM, using the player's decoder and the AV receiver's DAC.
  • Over HDMI 1.3 (or higher) connections as the original DTS-HD Master Audio bitstream, with decoding and DAC both done by the AV receiver.

This seems to suggest it's being sent as linear PCM when using plex.


Edited by D34DC3N73R, 26 March 2019 - 07:28 PM.


#11 ebr OFFLINE  

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Posted 27 March 2019 - 10:47 AM

Plex is transcoding it too they are just doing it in the app.

 

Your setup does not support DTS (of any flavor) so we are converting it to DD so that you get your 5.1 sound.

 

Was there a playback or audio problem?



#12 D34DC3N73R OFFLINE  

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Posted 27 March 2019 - 02:04 PM

Plex is transcoding it too they are just doing it in the app.

 

Your setup does not support DTS (of any flavor) so we are converting it to DD so that you get your 5.1 sound.

 

Was there a playback or audio problem?

 

It's the root cause of this playback issue. If it didn't need to transcode, it would direct play and emby wouldn't have to transcode 4k content (or have that transcoding error). Should emby only be transcoding audio in this circumstance? Because it seems to transcode both audio and video in this case. I'm not quite understanding how my setup doesn't support DTS. The Shield has DTS support, my TV has DTS support, and the soundbar has DTS support. DTS-HD should go to the TV and be backward compatible, thus sending the DTS track to the soundbar.  

 

So my choices currently are: downmix absolutely everything to stereo or transcode serverside (which has its own set of problems)?



#13 ebr OFFLINE  

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Posted 27 March 2019 - 02:10 PM

Your system, as currently connected/configured, does not support passing through DTS (do you see any DTS options in the playback settings in the app?).  I, like the previous poster, suspect this is due to the ARC not supporting it.

 

According to the ffmpeg log you posted, the only thing being converted is the audio:

  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (dts (dca) -> ac3 (native))



#14 MRobi OFFLINE  

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Posted 27 March 2019 - 07:00 PM

It's the root cause of this playback issue. If it didn't need to transcode, it would direct play and emby wouldn't have to transcode 4k content (or have that transcoding error). Should emby only be transcoding audio in this circumstance? Because it seems to transcode both audio and video in this case. I'm not quite understanding how my setup doesn't support DTS. The Shield has DTS support, my TV has DTS support, and the soundbar has DTS support. DTS-HD should go to the TV and be backward compatible, thus sending the DTS track to the soundbar.  

 

So my choices currently are: downmix absolutely everything to stereo or transcode serverside (which has its own set of problems)?

It doesn't support it because you are hooked up through HDMI-ARC. HDMI-ARC lacks the ability to transfer the full DTS-HD signal. So your soundbar doesn't receive it. Picture trying to push a watermelon through a garden hose. It's too big. The DTS-HD signal is the watermelon, the HDMI-ARC connection is the garden hose.

 

Your setup as it sits goes SHIELD ---> TV ----> Soundbar

Your setup for DTS-HD SHOULD go SHIELD ---> Soundbar ----> TV

 

If you've confirmed your polk soundbar does support DTS-HD, going shield-soundbar-tv is the only way you will be able to make use of that.

 

ARC should be used when you want to use the built-in apps of your smart tv through your soundbar. If you've got a shield, odds are good that any built-in app from your tv can also be added to the shield. If you want to connect more than 1 device to your soundbar (ie: blueray player, cable receiver, etc..) I recommend an HDMI switch instead of using HDMI-ARC.

 

If the newer audio formats are a priority, ARC should not even be in your vocabulary.


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#15 HRSCR OFFLINE  

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Posted 28 March 2019 - 08:19 AM

https://hometheaterr...return-channel/

 

 

"Firstly, a little background. HDMI Audio Return Channel (ARC) is based on the IEC 60958-1 specification, which is essentially the S/PDIF audio spec. There's two types of ARC in HDMI; Single Mode and Common Mode, but unfortunately we don't get informed as to which type any given product supports. 

Single Mode ARC uses a single wire in the HDMI link, with performance limited to around 3Mbps. This enables support for 2.0 LPCM and "lossy" compressed surround formats including Dolby Digital and DTS 5.1, but nothing more. Cable length is a huge factor with Single mode, with reliability typically getting flaky beyond about 7-8m in a passive HDMI cable. 

Common Mode ARC is superior, but less common (excusing the pun) in terms of deployment. It's still based on the same S/PDIF spec, but can theoretically support up to around 12Mbps. This is enough to carry 24-bit 192kHz 2-channel audio, or — to the point of this blog  a Dolby format called E-AC-3, which we know better as Dolby Digital Plus. This can also carry Metadata-enhanced Audio Transmission (MAT), being audio objects; aka Atmos.

So existing HDMI ARC can potentially support Dolby Atmos by maxing out the Common mode capability with an MAT stream. But there's a huge catch. Two, actually; 
 

  1. Channel count & resolution — while E-AC-3 can support up to 15.1 channels of audio, it's well beyond the HDMI ARC spec. Even getting 7.1 channels to pass is a stretch, so even if the stream contains object metadata, it will lack the resolution and height speakers. 
  2. System support — getting Atmos to work through HDMI ARC requires Common mode support in both the TV and AVR, and a high integrity link in-between. Even then, performance will be marginal.

HDMI 2.1 will change things considerably. It introduces enhanced ARC, or eARC for short, which can support up to twelve times the bandwidth of ARC, supporting up to 32 channels of 24-bit 192kHz audio! That is, eARC will support all of the same audio formats upstream as what we can already get in a downstream HDMI link.  

In summary, a basic, lower resolution form of Dolby Atmos may work through existing HDMI ARC, but it is highly system and link dependent. This is why we tend to generalise that ARC doesn't support Atmos, as it's out of spec and can't be relied upon. If you are designing this capability into systems, sticking with proven product combinations and short connectivity can give your systems an edge until eARC comes along and opens up our options." from: http://community.ced...s-over-hdmi-arc


Edited by HRSCR, 28 March 2019 - 08:29 AM.


#16 HRSCR OFFLINE  

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Posted 28 March 2019 - 08:33 AM

Bottom line

Audio Return Channel is convenient and can simplify your setup. However, it might also mean you don't get surround sound, and it definitely means you won't get the high-resolution audio formats from Blu-ray.

So for the best sound quality, it's still recommended to use individual HDMI cables to link to a sound bar or receiver when you can.



#17 Spaceboy ONLINE  

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Posted 28 March 2019 - 09:26 AM

Bottom line

Audio Return Channel is convenient and can simplify your setup. However, it might also mean you don't get surround sound, and it definitely means you won't get the high-resolution audio formats from Blu-ray.

So for the best sound quality, it's still recommended to use individual HDMI cables to link to a sound bar or receiver when you can.

arc works fine for me with a Samsung tv and Yamaha soundbar

#18 HRSCR OFFLINE  

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Posted 28 March 2019 - 09:44 AM

arc works fine for me with a Samsung tv and Yamaha soundbar

 

It could be, but the restriction of bandwith is there, is real, ARC is documented (speaking of sound) and not a problem to control devices.

 

The audio return is the problem, not the direct audio.



#19 Spaceboy ONLINE  

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Posted 28 March 2019 - 09:51 AM

It could be, but the restriction of bandwith is there, is real, ARC is documented (speaking of sound) and not a problem to control devices.

The audio return is the problem, not the direct audio.

yeah I wasn’t being dismissive, I thought it was an interesting observation which I will keep an eye out for. Aren’t there better quality leads that can help or is that just marketing blah?
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#20 ebr OFFLINE  

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Posted 28 March 2019 - 10:20 AM

yeah I wasn’t being dismissive, I thought it was an interesting observation which I will keep an eye out for. Aren’t there better quality leads that can help or is that just marketing blah?

 

That's mostly marketing (assuming you are using a high-bandwidth HDMI cable in the first place).


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