Audio demuxed with eac3to, is the channel order correct ?

[madhatter300871]

Hi

I have de-muxed a few ac3, dts, dts-ma and dts-core tracks from a few blurays and when I examine the demuxed audio with mediainfo all of the streams show a channel order of L,C,R,SL,SR,LFE.

That's correct for AC-3 but DTS is meant to be C,L,R,SL,LR,LFE.

Does eac3to automatically re-map channels, or perhaps mediainfo is reporting channels wrong ... or maybe something I am missing !

I am now presuming that when I downmix with behappy (using avisynth to do the remapping) or perhaps just use avisynth NICAC3source / NICDTSsource and set it to downmix for me and only output stereo that the mix may be all screwed up because of this incorrect channel order on the DTS tracks !

Can any one shed any light on this ?



Cheers :)

[tebasuna51]

You don't need know the internal channel order in compressed audio, is a job for encoders/decoders.

A correct decoder output always the standard WAV channel order: L,R,C,LFE,SL,SR

This is the order inside AviSynth and don't need remap inside AviSynth.

A correct encoder accept the standard WAV order L,R,C,LFE,SL,SR and you don't need know how are stored inside the compressed audio.

BeHappy and eac3to was tested to obtain correct channel mapping, don't worry about that.

[b66pak]

with the exception on 3.0 ac3 (FL,FR,FC)...eac3to maps it as FL,FC,FR...
_

[tebasuna51]

with the exception on 3.0 ac3 (FL,FR,FC)...eac3to maps it as FL,FC,FR...
_

Yes, you are right.
I test eac3to-libav here: http://forum.doom9.org/showpost.php?p=1134394&postcount=4622

But now seems the 3/0.0 and 3/0.1 need a -0,2,1,3,4,5 remap using libav.

With the default Nero decoder the same remap is needed, also there are distorted channels in 2/0.1, 2/1.0, 3/0.0, 3/0.1, 3/1.0, 3/1.1 and 3/2.0. Use -libav for them.

No problem for standard channel config 2.0 and 3/2.1

[madhatter300871]

Hi

So bearing in mind that I have not decoded my stream yet, I am simply getting information about it using mediainfo, I have a few more questions :-

1. Why does the DTS stream show a channel order of L,C,R,SL,SR,LFE when it should be C,L,R,SL,LR,LFE ?

2. Is media info not showing me the channel order within the stream, is it showing me the channel order as it will be decoded ?

3. So if I now understand correctly, are you saying that it doesn't matter in what order the channels are within the original stream they will always be decoded as L,R,C,LFE,SL,SR ?

4. Does all "correctly" mastered audio have a WFE header, and therefore the channels can be encoded in any order and will always be decoded in the correct order of L,R,C,LFE,SL,SR ?

5. If I now use "getchannel" in avisynth, provided the decoder does its job correctly will the channel order always be 1=Left, 2=Right, 3=Centre, 4=LFE, 5=Surround left, 6=Surround right, regardless of the channel order of the source ?

Thanks for your help.

[tebasuna51]

1. I don't know, but is irrelevant

2. No, the decoded order must be L,R,C,LFE,SL,SR

3. Yes.

4. Yes.

5. Correct. At least NicAudio and BassAudio decoders work fine. We can't know DirectShowSource

[madhatter300871]

Thanks for the answers, it all seems to make sense now and also seems to be true with the tests I have done.

Using NicAudioSource I do get the correct channels with "getchannel".

I have not used BaseAudio, I dont really have much call to use it.

Using directshowsource (ffdshow) I did get mixed results. Out of interest, why can we not trust directshow filters to get the channel order correct ?