confused - Amazon Prime Video and 5.1

[fatoldgit]

So I setup my brother in law with a 5.1 system (actually 5.0, skipped the sub.. .sub failed the WAF).

This is his first time with surround sound at the rip old age of 65.

He currently uses Amazon Prime Video via Firefox (on Linux, installed by me a while ago after WIn 10 become the cesspool it is).

After doing some research it was categorically stated in many places that Prime Video doesn't support surround sound via a web browser (maybe windows 10/11 with edge did, reported in some places, but not relevant to this setup). See for example https://www.primevideo.com/help?nodeId=GUX9FYHU5D8LC9EJ

His TV does have the Amazon Prime Video app (which is a DOG to use) and I setup HDMI ARC in anticipation that we would need to use the TV Prime Video app.

Just to make it clear, the signal path is:

- Linux selected sound device is HDMI
- PC goes into one of the HDMI inputs on the AVR
- The AVR single HDMI output goes into the HDMI ARC input on the TV with ARC enable

After testing an iso rip of a surround sound movie played back via VLC (just to ensure all channels were working via this) I then tested sound from the PC, initially playing stereo via the spotify Linux app.

I then played a Prime video movie via the Firefox web browser (ie. NOT a Prime video app which doesn't exist for linux) and I got surround sound. Tested other movies, all good.

This made us both very happy... beers all around.. much merriment.

But as noted, web searches will emphatically state that Prime video movies via a web browser is only stereo

So after the big intro above, did I fluke it somehow cause I have ARC enabled?

I WILL NOT be touching anything to try and work out why (in fact will document the config)... it works...I am very happy it does but confused!!!

Thanks,

Peter

 

[voodooless]

How did you verify that it works? What audio mode does the AVR show?

Likely the AVR is just upmixing to surround using of if the available upmixers.

 

[fatoldgit]

How did you verify that it works? What audio mode does the AVR show?

Likely the AVR is just upmixing to surround using of if the available upmixers.

As noted, outside of Prime video I used an iso rip of a DVD and played that via VLC (so I 100% know the system was working with a DD sound track).

When playing from Prime Video, the AVR is set to dolby digital and I validated this by checking each channel when playing a Prime Video stream via the browser.

So for example, dialog was only in the center speaker, the surrounds had the "stuff" I expect to hear (ambient stuff like birds in the background, cars passing, street noises, music for tension etc).

None of that stuff, especially what was heard in the surrounds would (in my experience) be there from upmixing... this was 100% surround content that couldn't be derived via some spatial processing (outside of 100% dolby digital processing).

I don't understand why Prime Video couldn't playback surround sound via a web browser when attached to an AVR. I would think that the browser gets a surround sound web stream from Amazon, passes this directly out the HDMI channel on the PC unmolested and onwards to be decoded in the AVR. I doubt they would say "hey the end point is a browser, lets only stream a stereo feed".

Maybe what was being stated in the web documents I saw was that a web browser with only a PC in the loop can only play stereo (makes sense given Dolby decoding is a paid for feature) and I read too much into these statements ... and these documents didn't account for a downstream AVR in the config.

Thanks,

Peter

 

[fatoldgit]

Thinking about this even more, as noted I think I read too much into the documents/search results I saw on the web and that the AVR is working just the same with a web browser as it would if playing back an actual DVD (or DVD rip), which is to say the data stream from amazon is passed transparently from the web browser, via the PC HDMI to the AVR.

Peter

 

[voodooless]

The AVR was never the issue.

The question is if the Linux browser supports bitstream audio and if the Linux audio subsystem gives this unaltered to the AVR.

I still find this highly suspect.

So for example, dialog was only in the center speaker, the surrounds had the "stuff" I expect to hear (ambient stuff like birds in the background, cars passing, street noises, music for tension etc).

That is exactly what these upmixers do.

Does the Linux volume control work when you play such a (supposedly) multichannel video? If so, it’s very unlikely that it’s bit streaming unless the Linux volume control would change the AVR volume setting via HDMI.

 

[fatoldgit]

The AVR was never the issue.

The question is if the Linux browser supports bitstream audio and if the Linux audio subsystem gives this unaltered to the AVR.

I still find this highly suspect.


That is exactly what these upmixers do.

Does the Linux volume control work when you play such a (supposedly) multichannel video? If so, it’s very unlikely that it’s bit streaming unless the Linux volume control would change the AVR volume setting via HDMI.

Since my last post (and before your last reply) I have been investigating how browsers and pulse audio handle a dolby digital stream.

Of course the search results are a shower of s**t, cause they cover stuff from years ago etc.

It appears that browsers do zip cause they don't have decoders and pulseaudio CAN send a bit stream onwards. If it doesn't (due to not being configured as such) it "appears" they send multi-channel PCM BUT in the case of dolby digital I doubt it has a decoder for dolby digital.

Anyways, as far as my brother in law is concerned, he is getting surround sound... the quality of said sound is irrelevant to him (i.e. he has just ya average bloke who has no pretensions with regard to sound quaiity) and he spent less than $US 600 on the whole thing so it's all low end.

With regard to upmixers.... I don't see where on the Linux side this could happen unless someone hacked dolby digital decoding which I am sure would invoke a law suite.

I will keep researching this and see where it leads.

Thanks,

Peter

 

[voodooless]

With regard to upmixers.... I don't see where on the Linux side this could happen unless someone hacked dolby digital decoding which I am sure would invoke a law suite.

Linux doesn't do that, but the AVR could be setup to do this.

 

[fatoldgit]

So this is my best guess on the "chain of custody".

(1) As per a note in a Kodi document (i.e. can be believed) in regard to pulse audio:

In order to allow passthrough to work with PulseAudio it MUST be set to use a 2.0 channel configuration. Despite the 2.0 setting this will still allow 5.1 audio from AC3, DTS, and EAC3.

(2) the pulseaudio config for the relevant bits (as per pulseaudio --dump-conf | egrep -i "mix|default-sample"):

enable-remixing = yes
remixing-use-all-sink-channels = yes
remixing-produce-lfe = no
remixing-consume-lfe = no
default-sample-format = s16le
default-sample-rate = 44100
default-sample-channels = 2

(3) the pulse audio doco states when remixing is used:

Whenever a stream has different channels than the sink it connects to, pulseaudio may apply a remixing algorithm.

(4) the pulse audio doco states what the remix params mean (interesting comment on enable-remixing):

enable-remixing

If disabled never upmix or downmix channels to different channel maps. Instead, do a simple name-based matching only. Defaults to yes. There is no known valid use case for setting this option to no, therefore, this option is deprecated and may be removed in a future version of PulseAudio.

remixing-use-all-sink-channels

If enabled, use all sink channels when remixing. Otherwise, remix to the minimal set of sink channels needed to reproduce all of the source channels. (This has no effect on LFE remixing.) Defaults to yes.


CONCLUSION BACKGROUND

- pulse audio will send a bit stream when set in a 2.0 channel configuration (which is my use case)
- Pulse audio will remix where the sink has a different number of channels
- The sink is the AVR HDMI input and additionally is set up for dolby digital


CONCLUSION

Because pulse audio in 2 channel mode allows bitstreaming and because the sink supports 6 channels (as used by dolby digital) we can conclude that no remixing takes place in Linux and that a bit stream is sent to the AVR for dolby digital processing.

Firefox does nothing with the data stream it handles because the data stream is not something it understands (i.e. it isnt HTML or CSS or a bit image or a pdf etc)

Thus I have to believe that the AVR is doing the native dolby decoding because it is getting a bit stream over HDMI

Thanks,

Peter

 

[ShadowBoxer]

Wouldn't it be simpler to just use a $30 Fire stick?