Is it possible to remove the atmos metadata from an eac3 track without reencoding ?

[NanoBot]

Hi everbody,

the subject tells it all: I want to remove the atmos metadata extension from an eac3 track to save space, but without the need to reencode this track. The tracks looks like that:

Format                                   : E-AC-3 JOC
Format/Info                              : Enhanced AC-3 with Joint Object Coding
Commercial name                          : Dolby Digital Plus with Dolby Atmos

Could anyone give me a hint how to achieve that ?

Thx in advance, NanoBot

[SeeMoreDigital]

Out of interest...

If it is possible to remove such meta-data, what would you intend to do with it. Or do you just want to delete it?

[NanoBot]

I just want to get rid of the metadata to save space when archiving a tv series. The german 5.1 DD+ track without Atmos metadata has a bitrate of 256kBit/s, while the english 5.1 DD+ track with Atmos metadata has a bitrate of 768kBit/s. But I will never need the Atmos metadata, since I will never buy such an audio equipment.

Therefore I am looking for a software which is able to extract the "pure" DD+ without the metadata, but without reencoding it to avoid a quality loss. After that, I would remux the new track into a Matroska file. See the "-core" parameter of eac3to, which is able to extract the DTS core from an DTS MA track, as analogy.

[tebasuna51]

I tried with:

ffmpeg -i DD+Atmos.eac3 -bsf:a eac3_core -c:a copy output.eac3

but the output is still Atmos with the same size.
Work with thd and the filter -bsf:a truehd_core

BTW if you want save space you can recode it at desired bitrate:

ffmpeg -i DD+Atmos.eac3 -acodec eac3 -ab 256k output.eac3

[NanoBot]

Of course I could reencode, but reencoding from one lossy format to another is never a good idea.

Perhaps I should have a look into the sources of lav filters, because the LAV audio decoder is able to decode the DD+ stream while ignoring the Atmos metadata. Maybe that I am able to learn how to differentiate the eac3 core and the metadata.

[tebasuna51]

Originally Posted by NanoBot

Of course I could reencode, but reencoding from one lossy format to another is never a good idea.

Also lose 3D metadata is a bad idea.

Recode a Atmos eac3 5.1 768 Kb/s to 512 Kb/s if you want a transparent recode.

I challenge you to difference both in a blind test over a 2D audio equipment.

[SeeMoreDigital]

Keep the original audio and video streams and buy bigger HDD's

[NanoBot]

First of all, the reason of my wish to reduce the size of the audio track is not that I am short on free hdd space. Instead the reason is, that on principle I want to keep only those components of a movie or tv series which are usefull for me, so I remove all audio and subtitle languages I don't understand and keep only the audio formats my equipment is capable to playback. And in fact, of course you are right, HDD space is very cheap this days, so normally there would be no need to be as frugal as possible.

But now I am wondering if I am on the wrong horse all the time. I thought that an eac3 track with atmos metadata could be seen like a DTS-MA track: A small DTS core and a much bigger MA extension to make it lossless and extend the channel number from 5.1 to 7.1. So when is comes to DTS-MA, removing the extension and just keeping the core is an easy way to save space. From your suggestions I now suppose, that things are different with eac3 + Atmos ? What I mean is, that removing the metadata will not save a noticeable amount of space ? If that assumption would be true, I will forget about removing the metadata and keep those audio tracks like they are.

[SeeMoreDigital]

Like most people I remove any audio and subtitle streams I don't require. That being said, if the Dolby Digital Plus audio sources are from Blu-ray discs, it should be possible to extract and keep their Dolby Digital core!

Much depends on your sources and how they've been encoded.