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Adjust bitrate for transcoded audio such as Dolby AC-3


Charlie117

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Charlie117

I'll try to keep this feature request short and simple.

 

When the Emby server needs to transcode audio to make it compatible for the Emby client, it will use a hardcoded value for the bitrate that cannot be changed.

For example, if the audio gets transcoded to Dolby Digital AC-3, it will always use a bitrate of 384 kb/s. This value cannot be changed, even though Dolby Digital AC-3 allows a maximum bitrate of 640 kb/s. Although 384 kb/s is a decent compromise between quality and data, it is very compressed and the quality is far from being transparent.

 

The same thing applies to every other audio codec the Emby server may transcode to, such as AAC.

 

So the request is simple, allow users to specify the bitrate that should be used for transcoding audio.

 

Thanks,

Charlie

 

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  • 2 months later...

I would also wish some kind of setting for the audio bitrate (or just transcode to 640kbps AC3 if the user didn't select a low bitrate in the client).

AC3 isn't a very efficient/good CODEC and ffmpeg isn't very good at encoding AC3. So 384kbps doesn't result in great quality for 5.1 channel sound.

Plex transcodes multichannel sound to 640kbps AC3 (at least for LAN bandwidth). Would be great if Emby could also use the highest allowed bitrate.  :)

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  • 2 weeks later...
Charlie117

AC3 isn't a very efficient/good CODEC and ffmpeg isn't very good at encoding AC3. So 384kbps doesn't result in great quality for 5.1 channel sound.

Exactly! It sounds awful on a decent 5.1 setup.

 

Really hoping to see this added someday. 

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  • 10 months later...
Jdiesel

640kbps is fine for optical. This limitation is likely a solution for an issues with some specific ATV TVs (Sony/Philips) that had issues with 640kbps ac3 audio. I'm not sure if this is even an issue anymore though

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Charlie117

You can't default to 640, fo people with optical, they won't get any audio. You could possibly squeeze 448.

 

Optical does allows DD 5.1 640 kbps and DTS 5.1 1509 kbps. Perhaps some devices don't? 

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Charlie117

Yes it certainly does.

 

I have confirmed this on my own set up many times. It supports both AC-3 640 kbps and DTS core 1509 kbps. I have never seen anyone claim otherwise until now.

That graphic is definitely incorrect. The person in that thread you linked to also confirms that DD 5.1 640 kbps works over S/PDIF:

Screenshot-2020-01-09-at-09-33-15.png

 

Also, official documentation from Dolby confirms that Dolby Digital (non-Plus) at 640 kbps bitrate can be sent over S/PDIF : https://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/dolby-digital-plus-faq.pdf

Dolby Digital Plus soundtracks are easily converted to a 640 kbps Dolby Digital signal without decoding and reencoding, for output via S/PDIF. The 640 kbps bit rate, which is higher than the standard 448 kbps used on DVDs, is fully compatible with all existing Dolby Digital decoding products such as A/V receivers, and can provide higher-than-DVD quality from Dolby Digital Plus soundtracks when played back through existing systems.

 

It also gets confirmed and discussed here: https://forum.kodi.tv/showthread.php?tid=304632&page=5

Edited by Charlie117
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Charlie117

Show me a log of the process to confirm it. I want to see the data.

 

You're literally the only person saying it's not true.. but I don't mind proving it just for you personally.

 

What do you need, an Emby log? If so, I'll need some time to prepare a S/PDIF setup as my current setup is all HDMI to my receiver.  

Edited by Charlie117
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Guest asrequested

You'll need to post a log from your device to show it isn't getting resampled. The server log won't prove anything. And there are multiple people on here that can't play that audio through optical. I've shown them how to resample to make it work.

Edited by Doofus
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Charlie117

Even though Dolby themselves say it's true, I'll make a S/PDIF setup and double check.

 

Any suggestions on how to obtain a device log? I have an Xbox One with an S/PDIF connection and also a Windows based PC that I believe supports S/PDIF. Will either of those work for a device log?

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Guest asrequested

S/PDIF isn't specific to optical, it's just the protocol. Example. mpv uses S/PDIF for all audio bitstreaming. In the log, the audio is always shown as S/PDIF stereo, but the audio details show it as 6 channel. We are talking about the physical entity of the fiber optic cable. It doesn't have the bandwidth, never has. Unless you can produce a log from the recipient end of the cable that shows 5.1 at 640Kb/s being decoded to raw audio, it isn't happening.

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Jdiesel

That's just not true, 2 channel 192hz/24bit PCM works just fine over toslink and that works out to about 4.6Mbps

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Jdiesel

Yes I don't think anyone is arguing that toshlink or coax supports multichannel uncompressed LPCM, it doesn't. What is being asked is why compressed DD is being transcoded to 384Kbps when 640Kbps is supported.

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Guest asrequested

Yes I don't think anyone is arguing that toshlink or coax supports multichannel uncompressed LPCM, it doesn't. What is being asked is why compressed DD is being transcoded to 384Kbps when 640Kbps is supported.

Everything that I've seen shows that AC3 5.1 640Kb/s won't work.

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Guest asrequested

I don't need trailers. I can make audio do whatever I want. Unfortunately, I don't have a 20ft optical cable, presently. I'll confess, I haven't actually tested this in a while. It might be interesting to acquire a long cable, and put it through its paces.

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Guest asrequested

Come to think of it, I'm not sure I have any devices with an optical output. My mini PC might...

 

Damn! It doesn't.

Edited by Doofus
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Charlie117

S/PDIF isn't specific to optical, it's just the protocol. Example. mpv uses S/PDIF for all audio bitstreaming. In the log, the audio is always shown as S/PDIF stereo, but the audio details show it as 6 channel. We are talking about the physical entity of the fiber optic cable. It doesn't have the bandwidth, never has. Unless you can produce a log from the recipient end of the cable that shows 5.1 at 640Kb/s being decoded to raw audio, it isn't happening.

 

Admittedly, I am mixing up terms here. But this is really not any useful contribution from your end.

 

You are the sole person here claiming something that is very controversial and unsupported except for some graphic featured in a  What HiFi article that isn't even discussed or mentioned again for the rest of the article. Numerous sources, including Dolby Laboratories themselves, confirm that 640 kbps is very much possible over the mentioned connection.

 

Now, instead of you proving your controversial statement, which would be common sense, I am offering to disprove it by confirming what has already been established as fact. To do that, I am asking your help in obtaining the device playback logs you are requesting, because I do not know how to retrieve them.

 

Also, this Wikipedia article about Toslink appears to directly contradicts your statement that "It doesn't have the bandwidth, never has" 

https://en.wikipedia.org/wiki/TOSLINK

Screenshot-2020-01-09-at-23-30-59.png

 

 

Unless you can produce a log from the recipient end of the cable that shows 5.1 at 640Kb/s being decoded to raw audio, it isn't happening.

 

Unless you are able to prove otherwise, it is most definitely happening. It is an established fact. DVDs have been using DD 5.1 448 kbps bitrate audio for more than a decade and several streaming services, including Netflix and Amazon Prime, are sending DD 5.1 640 kbps audio to their clients. You would expect a ton more issues with 640 kbps DD 5.1 if it wasn't 100% supported as it is.

Edited by Charlie117
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