MeGUI audio trascoding AC3 -> AAC

[mdjaved]

Hi everyone! I had a small question in relation to MeGUI audio encoding. I was trying to transcode an 5.1 AC3 to 5.1 AAC (MP4). I got the AC3 file from http://pessoal.onda.com.br/rjamorim/stuff/test.ac3.zip
(Thanks to rjamorim for posting that test file on the forum http://www.hydrogenaudio.org/forums/lofiversion/index.php/t18598.html)
After I encode, it seems my left front channel and left rear channel are combined together and so are my right front and rear channel. As for the centre channel, it seems to play from all speakers. I dont know what I've done wrong here. But any help would be appreciated. Btw, I used Nero for the encoding. I am attaching the encoded file as well as my settings on MeGUI and AC3Filter. I am sure its a silly error but I really wanna find it. Thanks for your time.

[tebasuna51]

Hi everyone! I had a small question in relation to MeGUI audio encoding. I was trying to transcode an 5.1 AC3 to 5.1 AAC (MP4)
....
After I encode, it seems my left front channel and left rear channel are combined together and so are my right front and rear channel. As for the centre channel, it seems to play from all speakers. I dont know what I've done wrong here.
Use BeHappy to transcode audio. Same decoder (NicAudio-AviSynth) and encoder (NeroAacEnc) than MeGUI but work fine.
I am attaching the encoded file as well as my settings on MeGUI and AC3Filter. I am sure its a silly error but I really wanna find it. Thanks for your time.
We can't see your attached file until approval, but maybe your file was downmixed from 5.1 to 2.0, and is a MeGUI problem, use this thread (http://forum.doom9.org/showthread.php?t=105920)to report.

[mdjaved]

Hi tebasuna51,
I tried using BeHappy v0.1.9.50201 and I chose the source as NicAc3Source and the destination as NeroDigital LC-AAC, ABR @ 256 kbit/s. I also disabled all the DSP (option [3]) and on option [2], I enabled only 'omit encoder script'. After transcoding, I still get the same output which means I'm screwing up somewhere else. Btw, this is the command-line equivalent that I found on BeHappy, encoder\neroAacEnc.exe -ignorelength -lc -br 256000 -if - -of "C:\Documents and Settings\Wild^Rain\Desktop\test files\ac3_test.mp4"
So like you suggested maybe its getting downmixed somewhere else. But I dont know where.

[mdjaved]

I found the problem. It seems the audio decoder of my media player (The KMPlayer) would by default downmix the playback from 5.1 to 2.0. Internally the file was 5.1 but the player would downmix to 2.0 and send it to the speakers. Its a great relief this is sorted. Now I can concentrate on video transcoding. Btw, I also noticed another issue on both BeHappy and MeGUI. When I choose ABR of 256 kbps, the final output has a bitrate of between 47-64 kbps. But when I choose CBR of 256, it is ok. Any idea why that happens?

[tebasuna51]

I found the problem. It seems the audio decoder of my media player (The KMPlayer) would by default downmix the playback from 5.1 to 2.0. Internally the file was 5.1 but the player would downmix to 2.0 and send it to the speakers. Its a great relief this is sorted.
Ok.
Btw, I also noticed another issue on both BeHappy and MeGUI. When I choose ABR of 256 kbps, the final output has a bitrate of between 47-64 kbps. But when I choose CBR of 256, it is ok. Any idea why that happens?

A true ABR encoding need always two pass (like the video: first pass to know the requirements, second pass to apply the different bitrates to match the desired average) and:
-2pass : Enables two-pass encoding mode.
Note that two-pass more requires a physical file as input, rather than stdin.
Then MeGUI/BeHappy can't use the correct method for ABR and you obtain something like VBR. I suggest you use always VBR with a quality between 0.3-0.4 to transcode ac3.