Kodi -> Receiver: Dolby/DTS Passthrough vs. Decode & Multichannel PCM?

Zarathustra[H]

Extremely [H]
Joined
Oct 29, 2000
Messages
33,824
Hey all,

So since getting my Denon AVR-x1300w receiver, I've been using Dolby/DTS passthrough mode, and it has been working well.

The Kodi team - however - just moved their latest version (Krypton, v17) to stable and it has kind of messed with my surround receiver.

First, I had no audio passthrough to my receiver at all, and then I found that I had to disable "sync playback to display" in order to get passthrough to work, but now I randomly have audio/video sync problems when watching live TV. (recorded and local files seem to work fine though)

Here is what I suspect happened:

After I upgraded to Krypton, passthrough stopped working all together. It required me to disable "Player -> Sync Playback to Display" for passthrough to work. In Jarvis this wasn't a requirement. The reason why is listed in the config description:

(Yes, this is Krypton, I just switched the skin back to Confluence, as I didn't want to have to teach everyone in the house how to use the TV again, they already complain it is too complicated)

32484947730_3e7c3bfbbd_z.jpg


So the reason is that if this is enabled, resampling might be required, and the assumption is that kodi can't resample passed through audio.

But then under System -> Audio -> Audio Passthrough there's this:

32712634212_a87abd1da4_z.jpg


It would seem as if AC3 transcoding would solve this sync problem. Is the fact that "Player -> Sync Playback to Display" is forced to be off in order to enable passthrough preventing the AC3 passthrough in the passthrough menu from working?

It seems like a mistake to disable passthrough if "sync playback to display" is enabled for this reason. Any thoughts?

The question is, how can I work around this for now?

What if, instead of using passthrough, I do all audio decoding in Kodi and present my receiver with multichannel PCM in 5.1?

If I have a 7.1 receiver (running with 5.1 speakers, two speakers are unpopulated for future upgrades) do I lose anything by going with this approach? I know it will probably increase CPU load on my Kodi box as it now has to do all the decoding, but it is a Haswell i5-4570T, so I think it can handle it no problem.

So, TLDR version, do I lose anything at all by moving to multichannel PCM with decode happening in Kodi instead of on my receiver? Will this fix my sync issue by allowing me to enable "sync playback to display"?

Also, is it better to have Kodi send the receiver 5.1 multichannel PCM to match my 5.1 speakers, or is it better to have Kodi send 7.1 multichannel PCM to my 7.1 receiver, and let my receiver use Neural X or some other tech to mix it down to my 5.1 speakers?

BulletDust, I'd greatly appreciate your input on this subject, as you seem very knowledgeable, and we just talked about this in another thread!
 
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Trimlock

[H]F Junkie
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Sep 23, 2005
Messages
15,228
If I were you I'd roll back and wait till they fix passthrough. I couldn't imagine not having passthrough Dolby hd/dts.
 

XvMMvX

[H]ard|Gawd
Joined
Jan 13, 2005
Messages
1,665
Everything you typed is why I finally ditched Kodi, MKV, and multiple sound formats. It is one problem after another and my household got annoyed with it. It has never really (nor was going to be) finished. My entertainment doesn't need to be an ongoing headache.

What sound gear are you running? Most people have at most a $2500 5.1 sound system. You can't really tell the difference in these sound formats on this level of gear.

I am making the move to apple tv and standardizing my file formatting.

If I ever have a home theater room with thousands of dollars in equipment I will worry about it then, which will probably never happen.
 

TType85

[H]ard|Gawd
Joined
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Messages
1,491
What sound gear are you running? Most people have at most a $2500 5.1 sound system. You can't really tell the difference in these sound formats on this level of gear.

This.

I moved from DefTech Pro Cinema 800 and Onkyo reciver (around a $1k for the whole system) to a mid-high end Dennon with DefTech SM65 bookshelf speakers for the L/C/R speakers (~400/ea retail) and I can hear the difference between AC3/DTS and the TrueHD/DTS-HD/MA tracks. With the old system there was very little to no difference.

I rip all my blu-rays with the HD Audio tracks and the regular audio tracks. For normal day to day use (what the wife uses) we play back using Plex on Roku's and I have yet to have one that doesn't play correctly. When I want to watch a movie that I care about the sound I switch over to the HTPC that bitstreams the audio (this is actually a VM running on my unraid box with a GT720 passed to it).
 

Zarathustra[H]

Extremely [H]
Joined
Oct 29, 2000
Messages
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Everything you typed is why I finally ditched Kodi, MKV, and multiple sound formats. It is one problem after another and my household got annoyed with it. It has never really (nor was going to be) finished. My entertainment doesn't need to be an ongoing headache.

What sound gear are you running? Most people have at most a $2500 5.1 sound system. You can't really tell the difference in these sound formats on this level of gear.

I am making the move to apple tv and standardizing my file formatting.

If I ever have a home theater room with thousands of dollars in equipment I will worry about it then, which will probably never happen.


Setup is in sig. It's not super high end by any means, but it's not terrible either:

Denon AVR-x1300w, Main: Infinity Primus 360, Centers: Infinity Beta 250, Surrounds: Micca mb42x, Sub: SVS SB12-NSD

32371281490_4121cff5f7_o.jpg


I know from other threads, my sub could be bigger, and at some point I want to upgrade the speakers, but they are fine for now.

I'm not really concerned about whether or not I'll hear a difference between the different encoding though, as much as I am about losing something if I have the Kodi box decode the AC3 or DTS streams and present it to the receiver as MultiChannel PCM, instead of having the receiver decode the streams.

If I were you I'd roll back and wait till they fix passthrough. I couldn't imagine not having passthrough Dolby hd/dts.

Theoretically they should be the same, especially since I think I've read that Kodi can properly decode both DTS:X and Atmos now, but I am not 100% sure. You know, theory and practice aren't always the same.
 

XvMMvX

[H]ard|Gawd
Joined
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Messages
1,665
Setup is in sig. It's not super high end by any means, but it's not terrible either:

Denon AVR-x1300w, Main: Infinity Primus 360, Centers: Infinity Beta 250, Surrounds: Micca mb42x, Sub: SVS SB12-NSD

32371281490_4121cff5f7_o.jpg


I know from other threads, my sub could be bigger, and at some point I want to upgrade the speakers, but they are fine for now.

I'm not really concerned about whether or not I'll hear a difference between the different encoding though, as much as I am about losing something if I have the Kodi box decode the AC3 or DTS streams and present it to the receiver as MultiChannel PCM, instead of having the receiver decode the streams.



Theoretically they should be the same, especially since I think I've read that Kodi can properly decode both DTS:X and Atmos now, but I am not 100% sure. You know, theory and practice aren't always the same.

I sit corrected, That is a nice setup.

I would definitely try to find a way to pass through the audio. I would still ditch Kodi, the developers treat it like an on going project and always break things while adding new features.
 
Joined
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To understand how Kodi processes audio you must first have a basic understanding of how audio in the digital domain works.

When analog audio is converted into the digital domain the near universal format used is Pulse Code Modulation (PCM). All manipulation of audio in the digital domain is always done on audio in the PCM format, therefore functions in Kodi such as volume control can only be done on PCM data, therefore if audio is in one of the Encoded Formats Kodi must decode the audio to PCM in order to manipulate it for volume control.

In other word, when enable Dolby digital (AC3) capable Receiver, Kodi will automatically attempt to direct play AC3 audio if the audio in PCM format, but if the video/container are not compatible then you will get no audio at all.

To solve no sound with Kodi issues, you can go to Settings/System/Audio output settings as a reference method. If the encoded formats of your video file is just the one that Kodi can not decode, you have two choice: one, transcode the video/container to the Kodi enable decode one, second, give up.
 

Zarathustra[H]

Extremely [H]
Joined
Oct 29, 2000
Messages
33,824
To understand how Kodi processes audio you must first have a basic understanding of how audio in the digital domain works.

When analog audio is converted into the digital domain the near universal format used is Pulse Code Modulation (PCM). All manipulation of audio in the digital domain is always done on audio in the PCM format, therefore functions in Kodi such as volume control can only be done on PCM data, therefore if audio is in one of the Encoded Formats Kodi must decode the audio to PCM in order to manipulate it for volume control.

In other word, when enable Dolby digital (AC3) capable Receiver, Kodi will automatically attempt to direct play AC3 audio if the audio in PCM format, but if the video/container are not compatible then you will get no audio at all.

To solve no sound with Kodi issues, you can go to Settings/System/Audio output settings as a reference method. If the encoded formats of your video file is just the one that Kodi can not decode, you have two choice: one, transcode the video/container to the Kodi enable decode one, second, give up.


1.) The issue here wasn't "no sound" but rather that there were audio syncing issues when passthrough was used. These didn't occur in Jarvis, but did occur in Krypton. Something changed between those two releases.

2.) This thread is 8 months old. Since posting this, I have just been running in multichannel PCM mode. I ahve also switched receivers, and switched from a home-brew ubuntu based Kodi install to OpenElec, so maybe it is worth trying passthrough again and seeing if it works now.

3.) That being said, I'm not even sure if passthrough has any benefits compared to multichannel PCM mode. Maybe decoding the audio on th ereceiver has some quality benefits compared to letting the FFMgpeg libraries do it in Kodi? Less CPU load maybe, but that's barely a concern. The kodi-box is somewhat overkill, and is fanless, so there is no fan noise issue.
 

Lunar

Limp Gawd
Joined
Jul 26, 2007
Messages
432
I'd recommend having kodi decode the audio and send out multichannel PCM. The only real difference is where the decode is taking place, Kodi or your receiver. As long as the PCM is being decoded correctly by Kodi there should be no loss in audio quality to your receiver. Also, this will eliminate something that personally irritates me, which is the time it takes for my receiver to switch to different decodes based on the data it's receiving from the device, in my case an NVIDIA Shield TV. If you are always outputting PCM and having your device handle the decode operation, then this switching never has to occur because the receiver is always receiving raw PCM.

EDIT: As an extra bit from personal experience, I've always found fussing around with getting passthrough to work outside of closed platforms (Blu-Ray players, game consoles, etc) to be more hassle than it's worth. I remember back when I was still using an HTPC running Windows 7 that I tried to make a single box to rule them all (gaming, streaming video, live tv, blu-ray playback), I ran into horrid issues with trying to get the DTS and Dolby HD formats to passthrough. PowerDVD just wouldn't do it even though I met all the requirements (HDCP, etc). I finally gave up and just used my PS3 for blu-rays. Now I use the Shield TV and various apps for live TV, indexing home media content/playback, and streaming video, and I use my Xbox One for blu-ray playback. Since doing this, all the frustrations have gone away.
 
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