Encode to 7.1 eac3 for free and volume adjustment

[j7n]

The JOC parameters are about 70 kbit/s, but not always the same size in every frame. The also don't seem to very compactly encoded, so the channel steering is coarse indeed. I don't see what is gained from removing them, except if you want a clean 5.1 mix on atmos-capable hardware. Then maybe, instead of removing JOC, it is possible to invalidate the data in place.

Is there a lot of duplication with these substreams that harms compression ratio? With 7.1 you get two complete channels that are redundant (summed side surround channels).

Discrete should be much better than Atmos, except who has 12 or more speakers in their room.

[hellgauss]

I did not performed tests, but the tools should be capable to create up to 10.2 audio. It is 100% NOT compatible with atmos, so don't use it on atmos audio files.

For basic settings (core type, bitrate core and bitrate dependent) just copy-paste one of the included .bat and edit the three "set" commands.

For advanced usage you have to play with md71 chanmap override, since ffmpeg_eac371 has fixed chanmap 1a00.

@tebasuna
If you only need your files to be played in your 5.1.2 setup, perhaps the best way to do that is to code as 5.1 core + 2 extra channels, so you save bitrate. Or 3.1 + 4, without channels replacement and without downmix.

PS for testers:
I would be very interested in knowing if, with this tool, an .mkv video with 7.1 audio with ac3 core plays well in DD hardware not DD+ capable, e.g. in a TV through USB. Has anyone performed this test?

[tebasuna51]

With the hellgauss method we create a standard 5.1 in independents frames (AC3 or EAC3 to be BD compliants or not) and a second stream 4-0 with dependents frames (always EAC3).
In the 5.1, the Ls/Rs pair have the downmix of original Ls/Rs and Lrs/Rrs.
In the 4.0 we have the originals Ls/Rs and Lrs/Rrs and with the "chanmap bit Location" 1a00 say: replace from 5.1 the Ls/Rs and add the Lrs/Rrs

If we have Atmos sources from decoders like Dolby Reference Player or Cavernize we can use the hellgauss method to create a specific EAC3 for our audio system:
5.1.2 Replacing L/R with L/R and add Vhl/Vhr (need a previous downmix L/R with Vhl/Vhr) chanmap: A010
5.1.2 Replacing Ls/Rs with Ls/Rs and Lts/Rts (work the same downmix than 7.1) chanmap: 1804
5.1.4 Adding the 4 new channels Vhl/Vhr and Lts/Rts (the core ignore those channels) chanmap: 0014
7.1.2 Adding Lrs/Rrs and Vhl/Vhr or Lts/Rts (the core ignore those channels) chanmap: 0210 or 0204

Maybe we can replace/add more channels if dependent frames add more channels but I think it is enough for standard players.
In my test I can generate now both 5.1.2 and 5.1.4 but not 7.1.2 (I still don't know for what)
The Atmos decoder can generate until 16 channels, of course I can't test that.

[tebasuna51]

Tree .bat to convert sources (Atmos decoded by Dolby Reference Player, aka DRP) 5.1.2, 5.1.4 and 7.1.2.

a) The 5.1.2: recognized by DRP with chanmap Ls/Rs-Lts/Rts but the audio Lts/Rts played in Ls/Rs speakers.
Decoded fine with ffmpeg recovering the same source and with maskchannel L R C LFE Ls Rs Tsl Tsr (MediaInfo channel names)

b) The 5.1.4: DRP show "Custom channel map: Ls, Rs, Lts/Rts" instead Vhl/Vhr-Lts/Rts chanmap: 0014. Only play in 5.1 speakers.
Decoded fine with ffmpeg recovering the same source and with maskchannel L R C LFE Ls Rs Tfl Tfr Tsl Tsr

c) The 7.1.2: DRP show "Not bitstream information available" but play 5.1 speakers.
ffmpeg can't recover the same source with a channel duplicated and other empty, the maskchannel is correct L R C LFE Ls Rs Lb Rb Tfl Tfr

[junh1024]

I tested a variety of extended 2D and 3D layouts (71w, 512 etc) with simplified settings but similar results as Teba - None of them would play in anything other than 5.1 using modern infrastructure (except for 71b) , but they mostly show up fine in FFMPEG-based apps.

If 512 doesn't work, theres no way 514 & 712 would work. 8.0 probably doesn't work.

DL input and samples: https://easyupload.io/b1xmb1

Simplified code below.

DragNDropHere_eac3Core2.zip

[hellgauss]

7.1b is the "standard" 7.1?

It can be tried a different channel mask in input for the 4channel source. This should change the acmod field (which however should be replaced by the channelmap)

Try this change for the 4ch encoding, rather than pan=quad

"pan=4.0|c0=c6|c1=c4|c2=c7|c3=c5"

you have to guess the correct channel input order for you setup, but as a first test if they are played it is ok.

According to Table 5.8 there are two different acmod for 4 speakers. Pan=quad set acmod=110. Pan=4.0 set acmod=101.