Audio Passthrough on LiveTV

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kszabo Offline
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Post: #31
my 5 cents to the topic: I used the same hardware with windows/mediaportal with audio passthrough on liveTV for years without any obvious problems. For me PCM transcoding is not a big show killer if it is done properly and makes liveTV more stable... we still have decent surround sound. I love the fast reaction time and stability of Kodis liveTV!
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noggin Offline
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Post: #32
(2017-02-13 02:58)nickr Wrote:  There should be no difference in sound quality, although if the audio coming from your TV broadcaster is EAC3 (ie extended not plain ac3) then another thread tells me there might be problems.

Set speakers on 5.1 (in kodi) if you have 5.1 real speakers.

That's only the case if the AV Receiver is doing a straight 5.1 decode in the same way that Kodi is. If the AVR has processing (dynamic range reduction etc.) that is based on the Dolby metadata then the audio won't be the same in both use cases. With passthrough the AVR receive metadata, with Kodi PCM decode it won't.

It's not a universal requirement - but I can understand the frustration of some in finding that passthrough has gone. Kodi does have to work in far more diverse use cases than consumer PVRs though - so I get the different requirements (particularly when it comes to display frame rates).

One thing that PVR live (and live-paused) viewing presumably has to disable is 'Sync playback to display', as that introduces asynchronous replay potentially?
(This post was last modified: 2017-02-23 13:24 by noggin.)
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nickr Offline
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Post: #33
I understand ffmpeg (and therefore Kodi) does respect Dolby metadata on decode, but I am no expert.

If I have helped you or increased your knowledge, click the 'thank user' button to give thanks :) (People with less than 20 posts won't see the "Thank you" button.)
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noggin Offline
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Post: #34
(2017-02-23 20:39)nickr Wrote:  I understand ffmpeg (and therefore Kodi) does respect Dolby metadata on decode, but I am no expert.

That's not the point nickr.

The issue is if downstream AVR processing uses the metadata to implement other stuff - for example DRC - to reduce dynamic range when watching at night - or if the amp downmixes from 5.1 to stereo for zone 2 listening, but keeps 5.1 for Zone 1 etc. where the metadata informs the downmix.

Bottom line - passthrough is always going to be preferable as it carries information downstream that PCM doesn't. You can potentially do more/better processing on a 5.1 AC3 signal with metadata than a 5.1 PCM signal without. (Ditto for E-AC3)

Sure - for many use cases - there is no difference between Kodi decode to PCM and AVR decode to PCM. However this isn't true in all use cases.

I can totally understand why Kodi has ditched passthrough for Live TV. It's just a shame that it has.
(This post was last modified: 2017-02-24 12:24 by noggin.)
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jjd-uk Online
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Post: #35
The point is the AVR shouldn't have to do any processing, as ideally Kodi should be doing that when decoding AC3 to PCM.
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noggin Offline
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Post: #36
(2017-02-24 12:56)jjd-uk Wrote:  The point is the AVR shouldn't have to do any processing, as ideally Kodi should be doing that when decoding AC3 to PCM.

I'm not talking about decoding - I'm talking about stuff like DRC (Dynamic Range Control) which uses metadata like DialNorm to process the audio once it has been decoded from AC3 to PCM. I'm not sure how much DRC processing Kodi allows for if any. (DRC is what allows you to improve the intelligibility of dialogue at lower overall listening levels, when the wide dynamic range that AC3 is often mixed in would otherwise render the loud bits too loud or the dialogue too quiet at lower listening levels)

The other scenario I detailed - off the top of my head - was 5.1 to 2.0 mixdown - which Dolby Metadata carries information about (there are multiple mix-down options that are available for content creators to use - and these are carried in the metadata. The big one is whether the 5.1 is mixed to be optimised for Lt/Rt or Lo/Ro mixdown). Sure Kodi can follow this mix down if it is configured to output 2.0 - but what if you using a multi-zone amp - where your primary speakers are 5.1, but your second zone speakers are 2.0. At that point the receiver has to do the mixdown. If it is being fed PCM 5.1 with no metadata, there is no way for the second zone mixdown to be implemented correctly - as the information required is not passed through to the receiver.

Both of the above cases COULD be OK if the transcode to Dolby option works - IF the metadata is passed through.
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kraka40 Offline
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Post: #37
i'm clearing missing something. Help and guidance appreciated.

with recorded playback I get full DD+ via HDMI passthrough no problem .. even when I play a live recording just viewed get nice DD+ via HDMI.

when I watch a live tv show I get (according to my AVR) a PCM 2/0/0 signal. No matter what I set the audio settings on Kodi to, I continue to get a stereo signal. Audio settings set at 5.1, i've used fixed, optimized, and best.

am I doing something wrong, or is this what is expected?
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skybird1980 Offline
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Post: #38
do you enabled sending all streams inside recording service? Smile
http://img.photobucket.com/albums/v295/_...ttings.png
right down all marks.
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kraka40 Offline
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Post: #39
I'm using mythtv which provides all streams as far as I have been able to tell .. I'll go back and look at the core settings. In meantime I've moved back to Kodi 16 .. really disappointing this has been removed. Understand the concern with live streams, but for all intents and purposes for mythtv users, the live stream is a recorded stream which is probably why so many mythtv users are perplexed by this change.
(This post was last modified: 2017-04-02 20:34 by kraka40.)
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kraka40 Offline
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Post: #40
I am continually confused by these audio settings..

So on Kodi 16 .. w / live broadcast my receiver is receiving DD+ 5.1 surround sound from Kodi. If for an active broadcast I turn passthrough off, receiver begins receiving PCM 2/0/0 signal. this is what I see in Kodi 17. When I look at the Audio debug information of the broadcast it provides the following info..

D(Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, 5.1(side), 448 kb/s)

Information on the broadcast shows 720p, Dolby Digital, 5.1, MPEG-2, 16:9

Not sure what's missing, but I only get DD5.1 on my receiver w/ passthrough on.

I'm using firetv via hdmi to AVR.
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