Vero 4k, S/PDIF Audio, AC-3 Transcoding Flag Missing?


just a question which comes into my mind rereading the thread Multichannel audio incorrectly mapped :
The Vero 2 has a special flag under settings -> system -> audio named AC-3 Transcoding especially for the S/PDIF users which should transcode non-pass-through multi channel to multi-channel AC-3 audio.

This flag/feature is not visible on my Vero 4K. Is this really missing or placed somewhere else? Otherwise it would mean that S/PDIF Vero 4K users are caught to 2.0 audio, original AC-3 and original core DTS.

Thx in advance for a clarification,

BTW: Actual OSMC 2017.10-1 installed.

Are you in “Settings Level: Expert” and have activated “Allow passthrough”


Switch to english and see if it makes a difference?
Basically the point is a linked point of “Dolby Digital (AC3)-faehiger Receiver”

Switched to English+Reboot, switched to skin Estuary+Reboot … no change. It’s not visible on my Vero 4K system.

Log set:

cat /sys/class/amhdmitx/amhdmitx0/aud_cap:

CodingType MaxChannels SamplingFreq SampleSize
PCM, 8 ch, 32/44.1/48/88.2/96/176.4/192 kHz, 16/20/24 bit
AC-3, 6 ch, 32/44.1/48 kHz, 16/24 bit
DTS, 6 ch, 32/44.1/48/88.2/96 kHz,  bit
Dobly_Digital+, 8 ch, 32/44.1/48 kHz,  bit
MAT, 8 ch, 48/96/192 kHz,  bit
DTS-HD, 8 ch, 44.1/48/88.2/96/176.4/192 kHz, 16 bit
OneBitAudio, 6 ch, 44.1 kHz,  bit

Addition: Also tried both Audio Output Devices AML-M8AUDIO, HDMI and Default(AML-M8AUDIO-Analog),PCM … still missing.

Think you need to be set to 2 for the speaker outputs


Confirmed. Seems counter-intuitive.

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Thank you @James_Arrowsmith and @grahamh! That is exactly the root cause for the Vero 4K behaviour in the Audio menu, here.

Well, I think for a normal user (like me) this dependency between speaker 2.0 setting, using S/PDIF and seeing the AC-3 transcode flag is NOT self-explanatory.
May I suggest to think about a separate Audio Output Device for S/PDIF on the Vero 4K where such dependencies will be automatically set and the speaker setup restricted? As far as I can see with S/PDIF only speaker 2.0 setup with LPCM 2.0 transcoding is valid and allowed. All other formats have to be pass-through AC-3 5.1 or pass-through DTS 5.1 including the AC-3 transcoding. So, any other speaker setting should be disallowed for S/PDIF to avoid unnecessary confusion and support requests, here.

Looking into this, but the linkages between channel count and visibility of the transcode option are baked into kodi (same on all platforms afaict).

If you have a moment, can you confirm that using transcode (with 2.0 channels inevitably set) a 5.1 file (not AC-3 - say a 5.1 flac) plays as 5.1 on your AVR? That’s the bit that’s counter-intuitive for me.

Hi Graham, sure will do but need some time today. Like Sam already stated it’s quite painful to re-arrange the settings on the most AVRs just for such tests.

I have been using these settings for quite some time on my pi as well… Honestly, it’s absolutely intuitive. As you already pointed out, only 2.0 pcm audio is possible via s/pdif or pass-through of dolby/dts. That I would assume to be known by users :wink:

I have always understood the audio settings menu in the way that the top audio decoder section is about the sound device and pcm output only (which means this part should only be set to 2.0 if using a s/pdif output device) and the bottom audio pass-through part is only about bitstream options available for the device set (Dolby, dts and transcode for s/pdif). If you see it that way, it’s completely intuitive! :sweat_smile:

On my pi, transcode works with 5.1 pcm audio sources like a charme when the s/pdif device is set to 2.0 :+1:t2: Don’t have my Vero around to test atm, but I’d assume it to act the same.

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No sweat as @Chillbo has reported. Confirmation on Vero would be good in due course.

If Sam would buy me a AVR, I could check myself :wink:

S/dif can only handle 2 channel pcm as limited bandwidth. But dd and Dts are compressed audio so you can stuff 6 channels down in the same space 2 channel pcm will fit.

5.1 aac can be transcoded on the fly to dd and you can then stuff that down the spdif for 5.1 as well

Ok, took the time to test again the specific FLAC 5.1 file with Vero4K HDMI+S/PDIF, LPCM+AC3 transcoding:

Output           Received     Missing   Hearable Mapping
Port +           Format       First
Transcoding                   Signal
Mode /                        Length

HDMI, 2.0+AC3    DD[3/2.1]    2 secs    FL->FL,FR->FR,FC->FC,SL->SL+RL,SR->SR+RR

SPDIF, 2.0+AC3   DD[3/2.1]    1 secs    FL->FL,FR->FR,FC->FC,SL->SL+RL,SR->SR+RR

HDMI, 2.0        LPCM[2/0]    2 secs    FL->FL,FR->FR,FC->FL+FR,SL->FL,SR->FR

SPDIF, 2.0       LPCM[2/0]    1 secs    FL->FL,FR->FR,FC->FL+FR,SL->FL,SR->FR

HDMI, 7.1        LPCM[3/4.1]  2 secs    FL->FL,FR->FR,FC->FC,SL->SL,SR->SR

SPDIF, 7.1       LPCM[2/0]    1 secs    FL->FL,FR->FR,FC->FL+FR,SL->FL,SR->FR


  • the source FLAC file does not contain an LFE signal although named “5.1”
  • the first second/seconds are missing when playing: HDMI always 2 seconds, SPDIF always 1 second
  • there is no other LPCM format with SPDIF than 2/0
  • the rear speakers seems to be mapped by the AVR if the rear signal is not present
  • HDMI + speaker 7.1 setup seems to send “something” on the rear channels that’s why the AVR does not make the “upscale” to 7.1 using the source side channels for the rear speakers
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Thanks for that, Jim. Just proves that trying to cater for all cases (and everyone’s perception of what is ‘correct’) is like nailing jelly to the wall.

Suggests that a workaround for the 8 channels being sent to HDMI for a 5.1 signal is to use passthrough with transcoding. The tradeoff is having to use compression/decompression.

Mmmhhh, I think the issue should be more verified why/what the Vero4k sends to SL, SR, RL and RR when mapping to 8 channel LPCM since the Pi makes this correct and even the format is LPCM 7.1 then, one pair of the side or rear speacker channels is completely empty given the AVR a chance to adapt that. It looks like with the Vero 4K all of these 4 surround and rear channels contain some signal although only SL+SR are “hearable”.

Regarding AC-3 transcoding is only available for those having an AVR or device being capable to decode this format. I think to remember that at least one of the affected folks somewhere talked about his device is only PCM aware.

I strongly support this! :+1::pray:

I think we now have everything for the what, thanks to all testers, and I think I know the why. Not quite got to the how to fix yet.