Whats the difference between AC3 and TrueHD AC3 core tracks

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preiner
Posts: 7
Joined: Wed Jun 28, 2023 5:33 am

Whats the difference between AC3 and TrueHD AC3 core tracks

Post by preiner » Tue Jul 04, 2023 4:44 pm

Hi,
My UHD disks come with Dolby TrueHD 7.1 (ATMOS) as well as AC3.

I need both because several of my playback systems dont have 7.1 yet and transcoding them in realtime causes extreme stuttering (even with my quadro card enabled)

When ripping the video, MakeMKV shows 3 audio tracks. They are (in order)

1 AC3
2 TrueHD 7.1
3 AC3 (core)

What is the difference between tracks 1 and 3? They SEEM to always contain the same audio stream.

I was guessing that somehow MMKV can rip out 5.1 from the 7.1 and maybe thats why its called "core".
But if thats correct, why show it? Every TrueHD released has to have an AC3 track already.

Is there any use case where I would need / prefer this track?

Lastly. Is there a selection string that would automatically deselect this track?

Thanks for any help here.

Ezatoka
Posts: 409
Joined: Fri Dec 06, 2019 6:55 pm

Re: Whats the difference between AC3 and TrueHD AC3 core tracks

Post by Ezatoka » Tue Jul 04, 2023 5:43 pm

preiner wrote:
Tue Jul 04, 2023 4:44 pm
I was guessing that somehow MMKV can rip out 5.1 from the 7.1 and maybe thats why its called "core".
But if thats correct, why show it? Every TrueHD released has to have an AC3 track already.
Yes, it does take the core audio from the higher quality version. But you are incorrect to say, that every disc would have a single AC3 track.

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preiner
Posts: 7
Joined: Wed Jun 28, 2023 5:33 am

Re: Whats the difference between AC3 and TrueHD AC3 core tracks

Post by preiner » Wed Jul 05, 2023 3:44 pm

Thanks for the clarification.
Is there a reason why there would be an AC3 track listed as default as well as the AC3 core track when they both contain same content?

I would understand if one was alternate dialog or similar.

I ask because Im trying to reduce confusion during playback. All of my Emby devices ignore the audio track name that I assign (such as commentary) and instead only display AC3 or ATMOS.

Family ends up seeing multiple streams labeled AC3 with no description.

Additionally im not sure how to write a selection string that would remove the AC3 track. I dont think -sel:AC3 is valid.

In fact I cant find any list of valid tokens. Like is -sel:5.1 valid?

Argh.

Ezatoka
Posts: 409
Joined: Fri Dec 06, 2019 6:55 pm

Re: Whats the difference between AC3 and TrueHD AC3 core tracks

Post by Ezatoka » Wed Jul 05, 2023 3:57 pm

I cannot give a distinctive answer. All I can add is, that I had BluRays, where there was a 5.1 DTS track as well as a 5.1 PCM track of the same language. And they also contained the same audio content. I guess, the muxers might add those tracks for being the most compatible with all kind of players.

dcoke22
Posts: 3108
Joined: Wed Jul 22, 2020 11:25 pm

Re: Whats the difference between AC3 and TrueHD AC3 core tracks

Post by dcoke22 » Wed Jul 05, 2023 4:14 pm

Someone else had a similar question recently: viewtopic.php?f=8&t=31340

I don't have any experience with Emby (I use Plex). I'm surprised that Emby can't find the lossy core of one of the lossless formats and use it without transcoding.

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