How to embed a AC3 core into Dolby Digital Plus?

[DJ Bobo]

Hi guys
My original source has E-AC3 sound (without core), but when I try to burn it as BD or UBD, the sound won't play on the PS5.
My understanding is that even UBD needs a core AC3 to be embedded into Dolby Digital Plus to be compliant.
How do I achieve that?

[tebasuna51]

AFAIK you need recode the full track, with a commercial encoder or, if it is a 7.1, with the hellgauss method (https://forum.doom9.org/showthread.php?p=2016678#post2016678)

[DJ Bobo]

Damn.
It is 5.1
And the whole point is trying to preserve the original E-AC3 track without re-encoding it, and just embed a re-encoded AC3 version (with 384k or so) for compatibility purposes.

[hellgauss]

There is no 5.1 ac3 "embedding" for 5.1 eac3. You can try to re-encode the eac3 as a 5.1 ac3 and put both tracks on the disc.

ffmpeg -drc_scale 0 -i "source.eac3" -c:a ac3 -b:a 640k "output.ac3"

[kurkosdr]

"Dolby Digital Plus" refers to many things (because Dolby can't get its branding straight):

- A Dolby Digital 5.1 (AC3) core + additional channels (up to 7.1 in practice) encoded as a side-signal

- A Dolby Digital Plus 5.1 (E-AC3) bitstream (which is not backwards compatible with Dolby Digital 5.1/AC3)

- A Dolby Digital Plus 5.1 (E-AC3) core + additional channels or even Atmos object-based audio encoded as a side-signal

---

When it comes to Blu-ray (non-UHD) and Blu-ray 3D, only the first definition will work, since Blu-ray doesn't support E-AC3 as a mandatory format, only AC3.

So, you'll have to re-encode your E-AC3 to AC3 (plus a side-signal if you want 7.1 channels).

---

When it comes to UHD Blu-ray, Dolby Digital Plus may not be officially supported, but it's well-supported in practice. Have you tried with a Dolby Digital Plus 5.1 (E-AC3) stream for a start on your PS5?

[DJ Bobo]

@ hellgauss
Thanks. I use TMPGEnc Video Mastering Works for AC3 encoding, which should yield a better quality than FFMPEG... at least in theory :-3

@ kurkosdr
As said, I also tried burning it as UBD, and it is recognized as "Ultra-HD Blu-Ray" by the PS5, but still no sound :/
Guess I'll have to go the TrueHD route then :-S

[kurkosdr]

@ hellgauss
Thanks. I use TMPGEnc Video Mastering Works for AC3 encoding, which should yield a better quality than FFMPEG... at least in theory :-3

@ kurkosdr
As said, I also tried burning it as UBD, and it is recognized as "Ultra-HD Blu-Ray" by the PS5, but still no sound :/
Guess I'll have to go the TrueHD route then :-S
Have you made sure there is a Dolby Digital Plus 5.1 (E-AC3 5.1) core? Any additional channels (for 6.1 or 7.1) have to be encoded as a side-signal. MediaInfo is very good for discovering that. Just a guess, Dolby Digital Plus in UHD Blu-ray is unofficial anyway.

About TrueHD, it's optional on Blu-ray (regular and UHD), so you need to have an AC3 "companion stream" or whatever Dolby calls it (but an AC3 bitstream needs to exist for players that can't play TrueHD). If using an official Dolby encoder, it will probably create the AC3 "companion stream" for you, but verify the m2ts file with MediaInfo just in case.

Note: I guess if you want to convert your E-AC3 audio to Blu-ray-compatible audio losslessly, TrueHD or DTS-HD MA are indeed your only options.

[DJ Bobo]

Just a guess, Dolby Digital Plus in UHD Blu-ray is unofficial anyway
Afaik, it is officially supported, but only in the 1st form you mentionned. I tried it with a 7.1 sample @ 1152kbps (with 5.1 core at 640kbps), it works on the PS5.
But this case here is really a plain 5.1 E-AC3, without core (TsMuxer also does not detect a core).
I tried the TrueHD route with ffmpeg and thdmerge; works like a charm on the PS5, and much more efficient than DTS: the TrueHD track reached 1,3 Mbit/s only!

[kurkosdr]

Afaik, it is officially supported, but only in the 1st form you mentionned. I tried it with a 7.1 sample @ 1152kbps (with 5.1 core at 640kbps), it works on the PS5.
But this case here is really a plain 5.1 E-AC3, without core (TsMuxer also does not detect a core).
Yeah, I meant the 2nd and 3rd forms are unofficial on UHD Blu-ray (and now that I recall better, they may be only used for "extras" audio tracks like commentaries, not main content, and to provide lossy Atmos in addition to lossless TrueHD Atmos for home cinema setups that don't have eARC).

Anyway, if your plain E-AC3 5.1 didn't work on your PS5, then it's not supported, and AC-3 must be used where lossy Dolby audio is required (or AC3 core + side-signal, aka the 1st form).

I tried the TrueHD route with ffmpeg and thdmerge; works like a charm on the PS5, and much more efficient than DTS: the TrueHD track reached 1,3 Mbit/s only!
Sure, but TrueHD must have an AC3 "companion stream", otherwise you risk no audio on some Blu-ray players.

It's very easy to verify with MediaInfo, just put the disc into the drive (or mount the ISO), right-click on the m2ts file that has the TrueHD audio and click "Media Info". If you see an audio track with "Format" being "MLP FBA AC-3", you are good.

[SeeMoreDigital]

I guess it would be useful to have an application that could inject/create a 5.1 Dolby Digital core into a 5.1 or 7.1 Dolby Digital Plus stream...

[DJ Bobo]

@SeeMoreDigital
Absolutely.
One thing is for sure, ThdMerge is not the right tool for it: it would crash when I give it the ec3 audio instead of a thd track :(

Sure, but TrueHD must have an AC3 "companion stream", otherwise you risk no audio on some Blu-ray players
Yeah. It is then a question of how much quality do I want to sacrifice: put a basic 64k Mono AC3 as companion just to get by, or a Prologic mix, or even a full-blown 5.1 version.

[SeeMoreDigital]

@SeeMoreDigital
Absolutely.
One thing is for sure, ThdMerge is not the right tool for it: it would crash when I give it the ec3 audio instead of a thd track :(
In the past I have used UsEac3To to generate and add a 640kbps DD core/companion stream to an existing TrueHD stream.

Also, it's also possible to use TSmuxer GUI (v2.7.0) to generate and add a phantom DD core/companion stream to an existing TrueHD stream.

[hellgauss]

I guess it would be useful to have an application that could inject/create a 5.1 Dolby Digital core into a 5.1 or 7.1 Dolby Digital Plus stream...

AFAIK you cannot have a 5.1 ac3 core in a 5.1 eac3.

If you have a non blu-ray compliant 7.1 eac3, you can re-encode the eac3 core into an ac3 and remux to 7.1 using my tool md71. In this way surround channels of the full 7.1 will be untouched.

However you have to be careful while setting compression, dialnorm and dynamic range in the new ac3, accordingly to the source.

[SeeMoreDigital]

AFAIK you cannot have a 5.1 ac3 core in a 5.1 eac3.

If you have a non blu-ray compliant 7.1 eac3, you can re-encode the eac3 core into an ac3 and remux to 7.1 using my tool md71. In this way surround channels of the full 7.1 will be untouched.

That's interesting, so technically only a 7.1 DD+ stream with a 5.1 DD core is permissible under the Blu-ray specification.

I'll have to dig out and check through all the DD+ 'speaker test' samples I download from Dolby's web site to see which ones contain a 5.1 DD core...

[kurkosdr]

In the past I have used UsEac3To to generate and add a 640kbps DD core/companion stream to an existing TrueHD stream.

Also, it's also possible to use TSmuxer GUI (v2.7.0) to generate and add a phantom DD core/companion stream to an existing TrueHD stream.
It's not a "core" stream btw, the TrueHD bitrstream is independently decodable and does not extend the AC-3 stream, that's why I called it a "companion stream" (but if anyone knows how Dolby calls it, please correct me).

As you said, you can create a "phantom" AC-3 companion stream that's only silence and has 32kbps bitrate since the TrueHD stream does not depend on it in any way (but don't do that, it will make your Blu-ray not have audio in players that can't play TrueHD).

AFAIK you cannot have a 5.1 ac3 core in a 5.1 eac3.

If you have a non blu-ray compliant 7.1 eac3, you can re-encode the eac3 core into an ac3 and remux to 7.1 using my tool md71. In this way surround channels of the full 7.1 will be untouched.

However you have to be careful while setting compression, dialnorm and dynamic range in the new ac3, accordingly to the source.
Sure, but the non-surround channels will be affected when re-encoding eac3 core into ac3, and OP wants lossless conversion, that's why I said TrueHD and DTS-HD MA are the only options.

[SeeMoreDigital]

As you said, you can create a "phantom" AC-3 companion stream that's only silence and has 32kbps bitrate since the TrueHD stream does not depend on it in any way (but don't do that, it will make your Blu-ray not have audio in players that can't play TrueHD).I can confirm that the phantom DD companion stream TSmuxer GUI (v2.7.0) generates works fine with my OPPO when muxed into a Blu-ray folder/file set ;)

That being said, I still prefer to generate a 'full fat' DD companion stream using UsEac3To.

[kurkosdr]

I can confirm that the phantom DD companion stream TSmuxer GUI (v2.7.0) generates works fine with my OPPO when muxed into a Blu-ray folder/file set ;)

That being said, I still prefer to generate a 'full fat' DD companion stream using UsEac3To.
Can you define the term "phantom DD companion stream"? Like, what is the bitrate and channel number?

[DJ Bobo]

@ hellgauss
Why do you think it is not possible to have an AC3 core embedded into a DD+ track?
I mean, the way I see it, DD+ 7.1 goes up to 1024kbps on its own, and DD goes up to 640k, yet when you encode DD+ 7.1 for Blu-ray, the maximum bitrate is the exact sum of both: 1024+640=1664, 1152k being the minimum bitrate you can choose to have the full 640k for the AC3 core.
Now, DD+ is extremely efficient, which makes me wonder, if the AC3 core was not just embedded as an independent track, how come DD+ needs a whopping 512 to 1024kbps just to add 2 channels?!
You even say in your documentation "Extract the surround channels to create a 4ch dependent eac3 stream with ffmpeg_eac371". I understand that this means, the surround channels are mixed together in the AC3 (Left Surr = LS+LSb, and Right Surr = RS+RSb), but encoded discretely in the DD+ section; yet the bitrate is still way too high, even for 4 channels, as it is capped at 640k for 5.1 or less, so how come we can add the full 1024kbps, as if we were encoding the whole 7.1 alone?!

[SeeMoreDigital]

@ hellgauss
Why do you think it is not possible to have an AC3 core embedded into a DD+ track?
You can have a 5.1 Dolby Digital core within a 5.1 Dolby Digital Plus stream, indeed it's part of the Blu-ray standard.

If you manage to find a 'store bought' 2K or 4K Blu-ray discs encoded with 7.1 Dolby Digital Plus audio I'd be interested to know if it contains a regular Dolby Digital core...

[DJ Bobo]

If you manage to find a 'store bought' 2K or 4K Blu-ray discs encoded with 7.1 Dolby Digital Plus audio I'd be interested to know if it contains a regular Dolby Digital core...
Disney discs have.
Avatar for example: https://www.blu-ray.com/movies/Avatar-Fire-and-Ash-4K-Blu-ray/410189/

[hellgauss]

@ hellgauss
Why do you think it is not possible to have an AC3 core embedded into a DD+ track?
I mean, the way I see it, DD+ 7.1 goes up to 1024kbps on its own, and DD goes up to 640k, yet when you encode DD+ 7.1 for Blu-ray, the maximum bitrate is the exact sum of both: 1024+640=1664, 1152k being the minimum bitrate you can choose to have the full 640k for the AC3 core.
Now, DD+ is extremely efficient, which makes me wonder, if the AC3 core was not just embedded as an independent track, how come DD+ needs a whopping 512 to 1024kbps just to add 2 channels?!
You even say in your documentation "Extract the surround channels to create a 4ch dependent eac3 stream with ffmpeg_eac371". I understand that this means, the surround channels are mixed together in the AC3 (Left Surr = LS+LSb, and Right Surr = RS+RSb), but encoded discretely in the DD+ section; yet the bitrate is still way too high, even for 4 channels, as it is capped at 640k for 5.1 or less, so how come we can add the full 1024kbps, as if we were encoding the whole 7.1 alone?!

I read (fastly, it is 271 pages) the specs, if I understood correctly you cannot "embed" a 5.1 ac3 in a 5.1 eac3. Maybe you can have two 5.1 streams (one ac3 and one eac3) to ensure compatiblity, but IDK. Actually, the term "embed" is misleading, the corret terms perhaps is "interleaved".

Both for DD_ac3 and DD+_eac3 the maximum channels in a basic stream is 5.1. DD+ specs allows for 7.1 channels in one of the following:

A) 5.1 eac3 core + 4.0 eac3 dependent
B) 5.1 ac3 core + 4.0 eac3 dependent (bluray compliant)

[j7n]

There is no sense calling one independent stream a "core" of another independent stream with the same number of channels. You can have two audio tracks if you wish.

The extra bitrate in a 7.1 E-AC-3 stream indeed goes to the 4 rear channels. The front & side channels are limited to 640 kbit/s because AC-3 can't go higher. Using a bitrate that high is not necessarily a wise choice just because you can. Maybe 1024 kbit/s is better. The way I understand it, the extra stream contains 4 independent channels and the 2 side channels from the core are not used when outputting 7.1.

[DJ Bobo]

Yeah, just went through the technical paper, it says:
With 7.1-channel content, for example, the Dolby Digital Plus bitstream
contains a core audio packet with a 5.1 mix, plus an extension audio
packet containing the original 7.1 mix’s separate Left Surround, Right
Surround, Left Back, and Right Back channels. To ensure that no surround
information is lost in 5.1 playback, the surround channels of the 5.1 mix are
downmixed from the separate surround and back channels of the original
7.1 mix. For 7.1 playback, the Left, Center, and Right channels of the core
5.1 packet are used, but its two downmixed surround channels are replaced
by the four separate surround channels from the extension packet.
Source (https://professional.dolby.com/globalassets/dolby-digital-plus/dolby-digital-plus-audio-coding-tech-paper.pdf)

So basically, even if we find a way to embed an AC3 core into an existing pure DD+ track, it would just save the surround channels, as the front channels would still come from the AC3 core during playback.
No :thanks:

@j7n
Anything below 1152kbps would reduce the bitrate for the AC3 core below 640, which you would want to avoid, obviously.
Now that I understand this whole extension thing, anything over 1280k wouldn't make sense either, as 640 is more than plenty for 4 channels o.O

[SeeMoreDigital]

Disney discs have.
Avatar for example: https://www.blu-ray.com/movies/Avatar-Fire-and-Ash-4K-Blu-ray/410189/Nice one. So how about you buy this disc and discover if the 7.1 Dolby Digital Plus contains a 5.1 Dolby Digital core?

[DJ Bobo]

Nice one. So how about you buy this disc and discover if the 7.1 Dolby Digital Plus contains a 5.1 Dolby Digital core?
It has :D
You can check HERE (https://caps-a-holic.com/c.php?d1=15922&d2=15923&c=6049)
As mentionned by kurkosdr, it *must* have an AC3 core to be Blu-ray compliant.
And as I stated before, I tried burning my own UBD, and it didn't play the sound if the track was pure DD+, but happily played it if it had the AC3 core.