Down Sizing ATMOS or TrueHD 7.1

[worknstiff]

Hey guys, since the forum is quiet lately I thought I would ask jdobbs or anyone else on this esteemed forum how they are dealing with all the ATMOS or TrueHD 7.1 audio that is on most disks nowadays. I always used to keep 7.1 audio intact before ATMOS came along with the outrageous 5GB or more file sizes. I'm not willing to keep this on a BD25 project at the expense of the video. I have been happy to keep just the Core 5.1 @ 1500K but here lately keeping the core only gets me DD5.1 @448. How do I get better audio?

[gonca]

you could try stripping out the ATMOS metadata and just keep the thd part

[worknstiff]

Thanks gonca, which tool would you recommend for this purpose? I don't have much use for command line stuff but maybe I could find a GUI for it somewhere. Also are you talking about just keeping the TrueHD 7.1? I thought that that is what BD Rebuilder was converting to get the core 5.1 448K audio. Sorry if I am just being dumb (my normal resting state), lol.

[gonca]

I believe that ffmpeg can do it, so maybe one its GUIs will be usable
are you talking about just keeping the TrueHD 7.1
yes
no atmos

[tebasuna51]

I don't know if there are a free tool to keep only the TrueHD 7.1 and reject the Atmos metadata. BTW I don't think downsize it very much.

You can use ffmpeg to recode the Atmos to AC3 5.1 until 640 Kb/s, or to EAC3 5.1 to your desired bitrate (but not used in BD's).
To preserve 7.1 with free encoders you need use AAC, also not supported in BD's.

[SquallMX]

you could try stripping out the ATMOS metadata and just keep the thd part

(Removed, its actually possible), what I do is convert the original file to DTS-HD Master Audio 16 Bits, bitrate savings are enormous, in some cases going from 6500 Kbps to 2500 Kbps while still been a lossless track.

[richardpl]

Metadata should be only a few KB, but there is no way to strip it, what I do is convert the original file to DTS-HD Master Audio 16 Bits, bitrate savings are enormous, in some cases going from 6500 Kbps to 2500 Kbps while still been a lossless track.

This is not true at all. FFmpeg can remove ATMOS with truehd_core bitstream filter.

[worknstiff]

@ SquallMX; RE: what I do is convert the original file to DTS-HD Master Audio 16 Bits, bitrate savings are enormous, in some cases going from 6500 Kbps to 2500 Kbps while still been a lossless track.

That's exactly what I wish to do. What do you use to convert?

[tebasuna51]

You are right richardpl, I obtain the TrueHD without Atmos using:

ffmpeg -i Atmos.thd -bsf truehd_core -acodec copy No-Atmos.thd

And I'm was wrong, the downsize is really noticeable 4,5 GB -> 3.1 GB

If you want less size but better than the AC3 core with only 448 Kb/s you can recode for free to AC3 640 Kb/s 5.1 (max):

ffmpeg -i Atmos.thd -c:a ac3 -b:a 640k -center_mixlev 0.707 No-Atmos5.1.ac3

Size test using the unique TrueHD Atmos in spanish language than I know (Valerian...):
Original audio track, L: max 22 bits, average 20 bits.
Original audio track, R+C+BL+BR+SL+SR: max 24 bits, average 20 bits.
Original audio track, LFE: constant bit depth of 20 bits.
Duration ....: 8217,08417 sec., (2h. 16m. 57.08417s.)

Using 24 bits encodes
File Chan. Size Kb/s %
------------- ----- ------------- ---- ---
No-Atmos.w64 7.1 9.466.081.088 9216 100
Atmos.thd X.1 4.837.954.028 4710 51 (source)
No-Atmos.dtshd 7.1 3.911.958.756 3809 41
No-Atmos.thd 7.1 3.334.975.156 3247 35
No-Atmos.flac 7.1 2.944.181.915 2866 31
No-Atmos.ac3 5.1 657.367.040 640 6.9
No-Atmos.aac 7.1 643.377.934 626 6.8 (V 100)

Using 16 bits
File Chan. Size Kb/s %
------------- ----- ------------- ---- ---
No-Atmos.w64 7.1 6.310.720.768 6144 100
No-Atmos.dtshd 7.1 2.540.000.084 2473 40
No-Atmos.flac 7.1 1.730.972.249 1685 27

@worknstiff
If your TrueHD track is not 16 bits, like the mine, your dtshd downsampling to 16 bits is not lossless.

The truehd_core have less size than the dtshd 24 bits.
To encode to dtshd you need DtsHD Master Audio Suite really expensive.

EDIT: my choice is preserve the Atmos with a full 3D surround (I have a system Atmos 5.1.2)
I never use 7.1 no-Atmos because to obtain a 2D surround is enough 5.1 channels, then my choice was AC3 5.1 640 Kb/s without audible diference with lossless 5.1
If the AC3 core is only 448 Kb/s like here I recommend use MeGUI or BeHappy (32 bits) to downmix 7.1 to 5.1, using AudioLimiter.dll, and ffmpeg to recode to AC3 5.1

[SquallMX]

This is not true at all. FFmpeg can remove ATMOS with truehd_core bitstream filter.

Whoa, that's great!

[SquallMX]

EDIT:
If the AC3 core is only 448 Kb/s like here I recommend use MeGUI or BeHappy (32 bits) to downmix 7.1 to 5.1, using AudioLimiter.dll, and ffmpeg to recode to AC3 5.1

Nice findings tebasuna51:goodpost:

But, would a 448 kbps file encoded with an official Dolby software provide more quality than a 640 Kbps created with Aften or FFMPEG?, last time I check Aften was not using all the potential of the AC3 specs and had some volume issues when decoding on standalone devices.

[gonca]

If you want less size but better than the AC3 core with only 448 Kb/s you can recode for free to AC3 640 Kb/s 5.1 (max):
BD_RB might be able to do that already

But you might just as well strip out the ATMOS and use the 7.1 thd track

[tebasuna51]

But, would a 448 kbps file encoded with an official Dolby software provide more quality than a 640 Kbps created with Aften or FFMPEG?, last time I check Aften was not using all the potential of the AC3 specs and had some volume issues when decoding on standalone devices.

Nope, the ffmpeg encoder is better than Aften (https://forum.doom9.org/showthread.php?p=1794293#post1794293).

BD_RB might be able to do that already

Yes, with ffmpeg.

[gonca]

Actually, it might have been re-encoding the coreless hd track using aften or nicaudio
It has been a while so I am not 100% sure

[tebasuna51]

I never used BD_RB and maybe you are rigth about aften encoder (nicaudio is the avisynth decoder).
I download the last version v0.61.05 and I see some old soft in Tools subfolder.

Some tips for jdobbs about audio soft:

19/01/2008 aften.exe Obsolete must be replaced by ffmpeg
09/12/2011 aften2.exe Obsolete must be replaced by ffmpeg
10/01/2015 AudioLimiter.dll OK, seems the downmix use that plugin like I recommend.
11/03/2010 faac.exe Obsolete must be replaced by ffmpeg
14/07/2012 faad.exe Obsolete must be replaced by ffmpeg
30/11/2017 ffmpeg.exe maybe is better to upgrade it (the -bsf truehd_core is added in 2019)
27/08/2012 nicaudio.dll Thanks for use my last version but I recommend replace it with LSMASHSource.dll with HD audio support and much more codecs than NicAudio
24/08/2012 wavi.exe There are a new Chizuken version here (https://forum.doom9.org/showthread.php?p=1527102#post1527102) and a rewrite rewavi (https://github.com/wieslawsoltes/rewavi/releases)

[worknstiff]

Thanks tebasuna51, on your recommendation to use MeGUI or BeHappy to recode to AC3 5.1. I will have to try it. I have even been attempting to extract each channel to wav and then use SoundForge to create 5.1 output, but that creates a file that BD Rebuilder doesn't like to recognize. Plus it is a time consuming process when I can just use CloneBD and it will create 5.1 @640 from somewhere, lol.

Thanks again, tebasuna51! :thanks: