4 Channel AC3 to 4 Channel AAC

[Raven2x]

Alright I am attempting to encode a film's 4.0 AC3 track in MeGui but it always ends up converting it to 2.0. 5.1 tracks and 2.0 tracks convert without any channel losses. Can anyone tell me what could possibly be wrong.

[shon3i]

What encoder you use? Nero or CT? and what settings you use in MeGUI, did you select keep original channels? Probably you are i just ask

[Raven2x]

Originally Posted by shon3i

What encoder you use? Nero or CT? and what settings you use in MeGUI, did you select keep original channels? Probably you are i just ask

Nero
Force Decoding Through Directshow (unchecked)
Keep Original Channels
Increase Vol Auto (Check)
Improve Accuracy etc (Check)
Delay Correction No
Variable Bitrate = Q=.3
AAC Profile = Automatic

[Raven2x]

Any recommendations?

[tebasuna51]

Originally Posted by Raven2x

Alright I am attempting to encode a film's 4.0 AC3 track in MeGui but it always ends up converting it to 2.0. 5.1 tracks and 2.0 tracks convert without any channel losses. Can anyone tell me what could possibly be wrong.
...
Any recommendations?

Is not a easy problem because is not standard stream (4.0). I make some test and...:

The problem can be NicAudio decoder used in MEGUI, here is how decode different ac3 streams:
2/2.0 -> FL,FR,SL,SR ok
3/1.0 -> stereo downmix lt = 0,4xFL + 0,3xC + 0,3xS ...
2/2.1 -> FL,FR,SL,SR ? LFE missing
3/1.1 -> stereo downmix lt = 0,4xFL + 0,3xC + 0,3xS ... ? LFE missing
3/2.0 -> 6 channel FL,FR,C,LFEempty,SL,SR

The alternative is use Azid, with appropriate parameters works ok.

In the other hand NeroAacEnc seems only work with mono, stereo and 6channel.
CT aacPlus encoder support 4 channel.

With this info, if your 4.0 AC3 track is 2/2 (FL,FR,SL,SR) you still can use BeHappy to encode with CT aacPlus.
If your 4.0 is 3/1 (FL,C,FR,S) you need use:
azid -d3/1 -ol,r,c,sl your.ac3 output.wav

After you can encode to aac with BeHappy-CT aacPlus

Warning, the ac3 stream keep the info 2/2 or 3/1 but aac ignore this info. I don't know how this aac stream can be played.

My recommendation is convert this 4.0 to 5.1 (with empty channels) or 2.0 Dolby Prologic (I for 3/1, II for 2/2)

[Raven2x]

How would I go about going from 4.0 to 5.1 with empty channels?

[bond]

try quicktime

[tebasuna51]

Originally Posted by Raven2x

How would I go about going from 4.0 to 5.1 with empty channels?

If your ac3 is 2/2 you can use this file.avs like audio input in MEGUI:

a=NicAc3Source("D:\Your_2-2.ac3",DRC=0) # use your path, name and preferred Dynamic Range Compression parameter (0=not, 1=yes)
fl=GetChannel(a,1)
fr=GetChannel(a,2)
sl=GetChannel(a,3)
sr=GetChannel(a,4)
c =Tone(Audiolength(a),440,Audiorate(a),1,"silence")
lfe=c
MergeChannels(fl,fr,c,lfe,sl,sr)

Edit: if you obtain a error like:

Error:
MeGUI.AviSynthException: GetChannel: Attempted to request a channel that didn't exist!

your ac3 4.0 is 3/1 then:

If your ac3 is 3/1 you need decode before with:
azid -d3/1 -ol,r,c,sl your.ac3 output.wav

and after use this file.avs like audio input in MEGUI:

a=WavSource("D:\output.wav")
fl=GetChannel(a,1)
fr=GetChannel(a,2)
c =GetChannel(a,3)
sl=GetChannel(a,4)   #maybe with .Amplify(0.707) to preserve the global volume (sl duplicated in sr)
sr=sl
lfe=Tone(Audiolength(a),440,Audiorate(a),1,"silence")
MergeChannels(fl,fr,c,lfe,sl,sr)