Downmixing from Atmos - maintain Atmos metadata?

General questions or discussion about HandBrake, Video and/or audio transcoding, trends etc.
Post Reply
ckronengold
Posts: 47
Joined: Tue Jan 08, 2013 8:31 am

Downmixing from Atmos - maintain Atmos metadata?

Post by ckronengold » Mon Apr 08, 2019 2:17 pm

Description of problem or question:

Recently picked up an Roku Ultra, which can support Atmos, but only with Dolby Digital Plus (E-AC3). When I transcode an Atmos title from TrueHD, I don't see a way to maintain / extract the Atmos metadata to apply to the E-AC3 track. I don't believe (could be wrong) that the AC3 tracks that I'm passing through have the Atmos metadata.

Downmixing from TrueHD+Atmos has, to the best of my understanding, not maintained the Atmos metadata. I've been reading the forums and it seems like this was a known issue (still an FFmpeg issue?).

Was just curious if it had been solved and I can't find the solution, or if its still an issue and I should sit back and wait. Apologies if I'm just being a moron and can't find the answer that was already posted.

Steps to reproduce the problem (If Applicable):
Passthru of TrueHD
Passthru of AC3
Transcode to AAC DPLII

HandBrake version (e.g., 1.0.0):
HB 1.2.2

Operating system and version (e.g., Ubuntu 16.04 LTS, macOS 10.13 High Sierra, Windows 10 Creators Update):
Win10 x64
Intel i5 3750
16 GB ram

ckronengold
Posts: 47
Joined: Tue Jan 08, 2013 8:31 am

Re: Downmixing from Atmos - maintain Atmos metadata?

Post by ckronengold » Mon Apr 15, 2019 1:13 pm

:bump:
nada?

Woodstock
Veteran User
Posts: 3214
Joined: Tue Aug 27, 2013 6:39 am

Re: Downmixing from Atmos - maintain Atmos metadata?

Post by Woodstock » Mon Apr 15, 2019 1:16 pm

Atmos is proprietary, and the meta data you are referring to wouldn't apply to a remix. Passing it through is really the only choice.

User avatar
Rodeo
HandBrake Team
Posts: 12196
Joined: Tue Mar 03, 2009 8:55 pm

Re: Downmixing from Atmos - maintain Atmos metadata?

Post by Rodeo » Mon Apr 15, 2019 5:12 pm

While it might technically be possible to split the Atmos extension from the TrueHD stream and attach it to an E-AC-3 re-encode of the TrueHD stream, I suspect it would not work as the Atmos must be tied to the audio stream it was authored for, and since TrueHD -> E-AC-3 is lossy it's likely the TrueHD track's Atmos data would not apply correctly to the re-encoded audio.

Since there is no public specification for Atmos, figuring it out would most likely require reverse engineering and hands-on testing with an actual Atmos setup. Given the workload and tedious nature of the task it might not be easy to find a developer interested in even trying to do this.

Though if you hear of any other open source software that implements it (now or in the future) feel free to let us know; there is indeed a use case for such a feature, should it actually be feasible.

Post Reply